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Bobbili KB, Singh B, Narahari A, Bulusu G, Surolia A, Swamy MJ. Chitooligosaccharide binding to CIA17 (Coccinia indica agglutinin). Thermodynamic characterization and formation of higher order complexes. Int J Biol Macromol 2019; 137:774-782. [DOI: 10.1016/j.ijbiomac.2019.06.211] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 06/21/2019] [Accepted: 06/26/2019] [Indexed: 10/26/2022]
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Paul A, Kumar P, Surolia A, Vijayan M. Biochemical and structural studies of mutants indicate concerted movement of the dimer interface and ligand-binding region of Mycobacterium tuberculosis pantothenate kinase. Acta Crystallogr F Struct Biol Commun 2017; 73:635-643. [PMID: 29095158 PMCID: PMC5683034 DOI: 10.1107/s2053230x17015667] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 10/27/2017] [Indexed: 11/11/2022] Open
Abstract
Two point mutants and the corresponding double mutant of Mycobacterium tuberculosis pantothenate kinase have been prepared and biochemically and structurally characterized. The mutants were designed to weaken the affinity of the enzyme for the feedback inhibitor CoA. The mutants exhibit reduced activity, which can be explained in terms of their structures. The crystals of the mutants are not isomorphous to any of the previously analysed crystals of the wild-type enzyme or its complexes. The mycobacterial enzyme and its homologous Escherichia coli enzyme exhibit structural differences in their nucleotide complexes in the dimer interface and the ligand-binding region. In three of the four crystallographically independent mutant molecules the structure is similar to that in the E. coli enzyme. Although the mutants involve changes in the CoA-binding region, the dimer interface and the ligand-binding region move in a concerted manner, an observation which might be important in enzyme action. This work demonstrates that the structure of the mycobacterial enzyme can be transformed into a structure similar to that of the E. coli enzyme through minor perturbations without external influences such as those involving ligand binding.
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Affiliation(s)
- A. Paul
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - P. Kumar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - A. Surolia
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - M. Vijayan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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Abhinav KV, Sharma K, Surolia A, Vijayan M. Distortion of the ligand molecule as a strategy for modulating binding affinity: Further studies involving complexes of jacalin with β-substituted disaccharides. IUBMB Life 2017; 69:72-78. [DOI: 10.1002/iub.1593] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 12/09/2016] [Indexed: 11/11/2022]
Affiliation(s)
- K. V. Abhinav
- Molecular Biophysics Unit; , Indian Institute of Science; Bangalore India
| | - Kaushal Sharma
- Molecular Biophysics Unit; , Indian Institute of Science; Bangalore India
| | - A. Surolia
- Molecular Biophysics Unit; , Indian Institute of Science; Bangalore India
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Arif SM, Geethanandan K, Mishra P, Surolia A, Varshney U, Vijayan M. Structural plasticity inMycobacterium tuberculosisuracil-DNA glycosylase (MtUng) and its functional implications. ACTA ACUST UNITED AC 2015; 71:1514-27. [DOI: 10.1107/s1399004715009311] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 05/15/2015] [Indexed: 12/29/2022]
Abstract
17 independent crystal structures of family I uracil-DNA glycosylase fromMycobacterium tuberculosis(MtUng) and its complexes with uracil and its derivatives, distributed among five distinct crystal forms, have been determined. Thermodynamic parameters of binding in the complexes have been measured using isothermal titration calorimetry. The two-domain protein exhibits open and closed conformations, suggesting that the closure of the domain on DNA binding involves conformational selection. Segmental mobility in the enzyme molecule is confined to a 32-residue stretch which plays a major role in DNA binding. Uracil and its derivatives can bind to the protein in two possible orientations. Only one of them is possible when there is a bulky substituent at the 5′ position. The crystal structures of the complexes provide a reasonable rationale for the observed thermodynamic parameters. In addition to providing fresh insights into the structure, plasticity and interactions of the protein molecule, the results of the present investigation provide a platform for structure-based inhibitor design.
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Abhinav KV, Sharma K, Swaminathan CP, Surolia A, Vijayan M. Jacalin-carbohydrate interactions: distortion of the ligand molecule as a determinant of affinity. ACTA ACUST UNITED AC 2015; 71:324-31. [PMID: 25664742 DOI: 10.1107/s139900471402553x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 11/21/2014] [Indexed: 11/10/2022]
Abstract
Jacalin is among the most thoroughly studied lectins. Its carbohydrate-binding site has also been well characterized. It has been postulated that the lower affinity of β-galactosides for jacalin compared with α-galactosides is caused by steric interactions of the substituents in the former with the protein. This issue has been explored energetically and structurally using different appropriate carbohydrate complexes of jacalin. It turns out that the earlier postulation is not correct. The interactions of the substituent with the binding site remain essentially the same irrespective of the anomeric nature of the substitution. This is achieved through a distortion of the sugar ring in β-galactosides. The difference in energy, and therefore in affinity, is caused by a distortion of the sugar ring in β-galactosides. The elucidation of this unprecedented distortion of the ligand as a strategy for modulating affinity is of general interest. The crystal structures also provide a rationale for the relative affinities of the different carbohydrate ligands for jacalin.
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Affiliation(s)
- K V Abhinav
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - Kaushal Sharma
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - C P Swaminathan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - A Surolia
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - M Vijayan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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Vijayan V, Khandelwal M, Manglani K, Gupta S, Surolia A. Methionine down-regulates TLR4/MyD88/NF-κB signalling in osteoclast precursors to reduce bone loss during osteoporosis. Br J Pharmacol 2014; 171:107-21. [PMID: 24111943 DOI: 10.1111/bph.12434] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Revised: 09/07/2013] [Accepted: 09/11/2013] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Studies have demonstrated that a moderate intake of amino acids is associated with development of bone health. Methionine, a sulphur-containing essential amino acid, has been largely implicated for improving cartilage formation, however its physiological significance on bone integrity and functionality have not been elucidated. We investigated whether methionine can prevent osteoporotic bone loss. EXPERIMENTAL APPROACH The anti-resorptive effect of methionine, (250 mg kg(-1) body wt administered in drinking water for 10 weeks), was evaluated in ovariectomized (OVX) rats by monitoring changes in bone turnover, formation of osteoclasts from blood-derived mononuclear cells and changes in the synthesis of pro-osteoclastogenic cytokines. KEY RESULTS Methionine improved bone density and significantly decreased the degree of osteoclast development from blood mononuclear cells in OVX rats, as indicated by decreased production of osteoclast markers tartarate resistant acid phosphatase b (TRAP5b) and MIP-1α. siRNA-mediated knockdown of myeloid differentiation primary response 88 [MyD88], a signalling molecule in the toll-like receptor (TLR) signalling cascade, abolished the synthesis of both TRAP5b and MIP-1α in developing osteoclasts. Methionine supplementation disrupted osteoclast development by inhibiting TLR-4/MyD88/NF-κB pathway. CONCLUSIONS AND IMPLICATIONS TLR-4/MyD88/NF-κB signalling pathway is integral for osteoclast development and this is down-regulated in osteoporotic system on methionine treatment. Methionine treatment could be beneficial for the treatment of postmenopausal osteoporosis.
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Affiliation(s)
- V Vijayan
- Molecular Sciences Laboratory, National Institute of Immunology, New Delhi, India
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Paul A, Mishra A, Surolia A, Vijayan M. Cloning, expression, purification, crystallization and preliminary X-ray studies of argininosuccinate lyase (Rv1659) from Mycobacterium tuberculosis. Acta Crystallogr Sect F Struct Biol Cryst Commun 2013; 69:1422-4. [PMID: 24316845 DOI: 10.1107/s1744309113031138] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Accepted: 11/12/2013] [Indexed: 11/10/2022]
Abstract
The last enzyme in the arginine-biosynthesis pathway, argininosuccinate lyase, from Mycobacterium tuberculosis has been cloned, expressed, purified and crystallized, and preliminary X-ray studies have been carried out on the crystals. The His-tagged tetrameric enzyme with a subunit molecular weight of 50.9 kDa crystallized with two tetramers in the asymmetric unit of the orthorhombic unit cell, space group P2(1)2(1)2(1). Molecular-replacement calculations and self-rotation calculations confirmed the space group and the tetrameric nature of the molecule.
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Affiliation(s)
- A Paul
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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Chetnani B, Kumar P, Abhinav KV, Chhibber M, Surolia A, Vijayan M. Location and conformation of pantothenate and its derivatives in Mycobacterium tuberculosis pantothenate kinase: insights into enzyme action. Acta Crystallogr D Biol Crystallogr 2011; 67:774-83. [PMID: 21904030 DOI: 10.1107/s0907444911024462] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 06/22/2011] [Indexed: 11/10/2022]
Abstract
Previous studies of complexes of Mycobacterium tuberculosis PanK (MtPanK) with nucleotide diphosphates and nonhydrolysable analogues of nucleoside triphosphates in the presence or the absence of pantothenate established that the enzyme has dual specificity for ATP and GTP, revealed the unusual movement of ligands during enzyme action and provided information on the effect of pantothenate on the location and conformation of the nucleotides at the beginning and the end of enzyme action. The X-ray analyses of the binary complexes of MtPanK with pantothenate, pantothenol and N-nonylpantothenamide reported here demonstrate that in the absence of nucleotide these ligands occupy, with a somewhat open conformation, a location similar to that occupied by phosphopantothenate in the `end' complexes, which differs distinctly from the location of pantothenate in the closed conformation in the ternary `initiation' complexes. The conformation and the location of the nucleotide were also different in the initiation and end complexes. An invariant arginine appears to play a critical role in the movement of ligands that takes place during enzyme action. The work presented here completes the description of the locations and conformations of nucleoside diphosphates and triphosphates and pantothenate in different binary and ternary complexes, and suggests a structural rationale for the movement of ligands during enzyme action. The present investigation also suggests that N-alkylpantothenamides could be phosphorylated by the enzyme in the same manner as pantothenate.
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Affiliation(s)
- Bhaskar Chetnani
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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Chetnani B, Kumar P, Surolia A, Vijayan M. M. tuberculosis pantothenate kinase: dual substrate specificity and unusual changes in ligand locations. J Mol Biol 2010; 400:171-85. [PMID: 20451532 DOI: 10.1016/j.jmb.2010.04.064] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 04/29/2010] [Accepted: 04/30/2010] [Indexed: 12/19/2022]
Abstract
Kinetic measurements of enzyme activity indicate that type I pantothenate kinase from Mycobacterium tuberculosis has dual substrate specificity for ATP and GTP, unlike the enzyme from Escherichia coli, which shows a higher specificity for ATP. A molecular explanation for the difference in the specificities of the two homologous enzymes is provided by the crystal structures of the complexes of the M. tuberculosis enzyme with (1) GMPPCP and pantothenate, (2) GDP and phosphopantothenate, (3) GDP, (4) GDP and pantothenate, (5) AMPPCP, and (6) GMPPCP, reported here, and the structures of the complexes of the two enzymes involving coenzyme A and different adenyl nucleotides reported earlier. The explanation is substantially based on two critical substitutions in the amino acid sequence and the local conformational change resulting from them. The structures also provide a rationale for the movement of ligands during the action of the mycobacterial enzyme. Dual specificity of the type exhibited by this enzyme is rare. The change in locations of ligands during action, observed in the case of the M. tuberculosis enzyme, is unusual, so is the striking difference between two homologous enzymes in the geometry of the binding site, locations of ligands, and specificity. Furthermore, the dual specificity of the mycobacterial enzyme appears to have been caused by a biological necessity.
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Affiliation(s)
- Bhaskar Chetnani
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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Chetnani B, Das S, Kumar P, Surolia A, Vijayan M. Mycobacterium tuberculosis pantothenate kinase: possible changes in location of ligands during enzyme action. Acta Crystallogr D Biol Crystallogr 2009; 65:312-25. [PMID: 19307712 DOI: 10.1107/s0907444909002170] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 01/16/2009] [Indexed: 11/11/2022]
Abstract
The crystal structures of complexes of Mycobacterium tuberculosis pantothenate kinase with the following ligands have been determined: (i) citrate; (ii) the nonhydrolysable ATP analogue AMPPCP and pantothenate (the initiation complex); (iii) ADP and phosphopantothenate resulting from phosphorylation of pantothenate by ATP in the crystal (the end complex); (iv) ATP and ADP, each with half occupancy, resulting from a quick soak of crystals in ATP (the intermediate complex); (v) CoA; (vi) ADP prepared by soaking and cocrystallization, which turned out to have identical structures, and (vii) ADP and pantothenate. Solution studies on CoA binding and catalytic activity have also been carried out. Unlike in the case of the homologous Escherichia coli enzyme, AMPPCP and ADP occupy different, though overlapping, locations in the respective complexes; the same is true of pantothenate in the initiation complex and phosphopantothenate in the end complex. The binding site of MtPanK is substantially preformed, while that of EcPanK exhibits considerable plasticity. The difference in the behaviour of the E. coli and M. tuberculosis enzymes could be explained in terms of changes in local structure resulting from substitutions. It is unusual for two homologous enzymes to exhibit such striking differences in action. Therefore, the results have to be treated with caution. However, the changes in the locations of ligands exhibited by M. tuberculosis pantothenate kinase are remarkable and novel.
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Affiliation(s)
- Bhaskar Chetnani
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Jyothi TC, Sinha S, Singh SA, Surolia A, Appu Rao AG. Napin from Brassica juncea: thermodynamic and structural analysis of stability. Biochim Biophys Acta 2007; 1774:907-19. [PMID: 17544981 DOI: 10.1016/j.bbapap.2007.04.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Revised: 04/19/2007] [Accepted: 04/19/2007] [Indexed: 11/22/2022]
Abstract
The napin from Brassica juncea, oriental mustard, is highly thermostable, proteolysis resistant and allergenic in nature. It consists of two subunits - one small (29 amino acid residues) and one large (86 amino acids residues) - held together by disulfide bonds. The thermal unfolding of napin has been followed by differential scanning calorimetry (DSC) and circular dichroism (CD) measurements. The thermal unfolding is characterized by a three state transition with T(M1) and T(M2) at 323.5 K and 335.8 K, respectively; DeltaC(P1) and DeltaC(P2) are 2.05 kcal mol(-1) K(-1) and 1.40 kcal mol(-1) K(-1), respectively. In the temperature range 310-318 K, the molecule undergoes dimerisation. Isothermal equilibrium unfolding by guanidinium hydrochloride also follows a three state transition, N <_-_-> I <_-_-> U with DeltaG(1H2O) and DeltaG(2H2O) values of 5.2 kcal mol(-1) and 5.1 kcal mol(-1) at 300 K, respectively. Excess heat capacity values obtained, are similar to those obtained from DSC measurements. There is an increase in hydrodynamic radius from 20 A to 35.0 A due to unfolding by guanidinium hydrochloride. In silico alignment of sequences of napin has revealed that the internal repeats (40%) spanning residues 31 to 60 and 73 to 109 are conserved in all Brassica species. The internal repeats may contribute to the greater stability of napin. A thorough understanding of the structure and stability of these proteins is essential before they can be exploited for genetic improvements for nutrition.
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Affiliation(s)
- T C Jyothi
- Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570020, India
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Natchiar SK, Suguna K, Surolia A, Vijayan M. Peanut agglutinin, a lectin with an unusual quaternary structure and interesting ligand binding properties. CRYSTALLOGR REV 2007. [DOI: 10.1080/08893110701382087] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Natchiar SK, Srinivas O, Mitra N, Surolia A, Jayaraman N, Vijayan M. Structural studies on peanut lectin complexed with disaccharides involving different linkages: further insights into the structure and interactions of the lectin. Acta Crystallogr D Biol Crystallogr 2006; 62:1413-21. [PMID: 17057347 DOI: 10.1107/s0907444906035712] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2006] [Accepted: 09/04/2006] [Indexed: 11/10/2022]
Abstract
Crystal structures of peanut lectin complexed with Galbeta1-3Gal, methyl-T-antigen, Galbeta1-6GalNAc, Galalpha1-3Gal and Galalpha1-6Glc and that of a crystal grown in the presence of Galalpha1-3Galbeta1-4Gal have been determined using data collected at 100 K. The use of water bridges as a strategy for generating carbohydrate specificity was previously deduced from the complexes of the lectin with lactose (Galbeta1-4Glc) and T-antigen (Galbeta1-3GalNAc). This has been confirmed by the analysis of the complexes with Galbeta1-3Gal and methyl-T-antigen (Galbeta1-3GalNAc-alpha-OMe). A detailed analysis of lectin-sugar interactions in the complexes shows that they are more extensive when the beta-anomer is involved in the linkage. As expected, the second sugar residue is ill-defined when the linkage is 1-->6. There are more than two dozen water molecules which occur in the hydration shells of all structures determined at resolutions better than 2.5 A. Most of them are involved in stabilizing the structure, particularly loops. Water molecules involved in lectin-sugar interactions are also substantially conserved. The lectin molecule is fairly rigid and does not appear to be affected by changes in temperature.
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Das S, Kumar P, Bhor V, Surolia A, Vijayan M. Invariance and variability in bacterial PanK: a study based on the crystal structure of Mycobacterium tuberculosis PanK. Acta Crystallogr D Biol Crystallogr 2006; 62:628-38. [PMID: 16699190 DOI: 10.1107/s0907444906012728] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Accepted: 04/07/2006] [Indexed: 11/10/2022]
Abstract
Pantothenate kinase (PanK) is a ubiquitous and essential enzyme that catalyzes the first step of the universal coenzyme A biosynthetic pathway. In this step, pantothenate (vitamin B(5)) is converted to 4'-phosphopantothenate, which subsequently forms coenzyme A in four enzymatic steps. The complex of this enzyme from Mycobacterium tuberculosis (MtPanK) with a derivative of the feedback inhibitor coenzyme A has been crystallized in two forms and its structure solved. The structure was refined in both forms using room-temperature and low-temperature X-ray data. In both forms, the MtPanK subunit has a mononucleotide-binding fold with a seven-stranded central beta-sheet and helices on either side. However, there is a small though significant difference in subunit association between the two forms. The structure is also grossly similar to the enzyme from Escherichia coli. The active-site pocket and the dimeric interface are on two opposite sides of the PanK subunit. The enzymes from M. tuberculosis and E. coli exhibit several differences, particularly at the dimeric interface. On the other hand, the coenzyme A-binding region is almost entirely conserved. A delineation of the invariant and variable features of the PanK structure further indicates that the dimeric interface is very variable, while the coenzyme A-binding site is substantially invariant. A sequence alignment involving various bacterial PanKs is in agreement with this conclusion. The strong correlation between structural plasticity, evolutionary conservation and variability and function exhibited by the molecule could be important in the design of species-specific inhibitors of the enzyme.
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Affiliation(s)
- Satyabrata Das
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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Krishna R, Manjunath GP, Kumar P, Surolia A, Chandra NR, Muniyappa K, Vijayan M. Crystallographic identification of an ordered C-terminal domain and a second nucleotide-binding site in RecA: new insights into allostery. Nucleic Acids Res 2006; 34:2186-95. [PMID: 16648362 PMCID: PMC1450331 DOI: 10.1093/nar/gkl107] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Revised: 09/16/2005] [Accepted: 03/08/2006] [Indexed: 11/13/2022] Open
Abstract
RecA protein is a crucial and central component of the homologous recombination and DNA repair machinery. Despite numerous studies on the protein, several issues concerning its action, including the allosteric regulation mechanism have remained unclear. Here we report, for the first time, a crystal structure of a complex of Mycobacterium smegmatis RecA (MsRecA) with dATP, which exhibits a fully ordered C-terminal domain, with a second dATP molecule bound to it. ATP binding is an essential step for all activities of RecA, since it triggers the formation of active nucleoprotein filaments. In the crystal filament, dATP at the first site communicates with a dATP of the second site of an adjacent subunit, through conserved residues, suggesting a new route for allosteric regulation. In addition, subtle but definite changes observed in the orientation of the nucleotide at the first site and in the positions of the segment preceding loop L2 as well as in the segment 102-105 situated between the 2 nt, all appear to be concerted and suggestive of a biological role for the second bound nucleotide.
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Affiliation(s)
- R. Krishna
- Molecular Biophysics Unit, Indian Institute of ScienceBangalore 560 012, India
- Department of Biochemistry, Indian Institute of ScienceBangalore 560 012, India
- Bioinformatics Centre and Supercomputer Education and Research Centre, Indian Institute of ScienceBangalore 560 012, India
| | - G. P. Manjunath
- Department of Biochemistry, Indian Institute of ScienceBangalore 560 012, India
| | - P. Kumar
- Molecular Biophysics Unit, Indian Institute of ScienceBangalore 560 012, India
- Department of Biochemistry, Indian Institute of ScienceBangalore 560 012, India
- Bioinformatics Centre and Supercomputer Education and Research Centre, Indian Institute of ScienceBangalore 560 012, India
| | - A. Surolia
- Molecular Biophysics Unit, Indian Institute of ScienceBangalore 560 012, India
- Department of Biochemistry, Indian Institute of ScienceBangalore 560 012, India
- Bioinformatics Centre and Supercomputer Education and Research Centre, Indian Institute of ScienceBangalore 560 012, India
| | - Nagasuma R. Chandra
- Bioinformatics Centre and Supercomputer Education and Research Centre, Indian Institute of ScienceBangalore 560 012, India
| | - K. Muniyappa
- Department of Biochemistry, Indian Institute of ScienceBangalore 560 012, India
| | - M. Vijayan
- Correspondence may also be addressed to M. Vijayan. Tel: +91 80 22932590; Fax: +91 80 23600535;
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Kulkarni KA, Samiksha K, Surolia A, Vijayan M, Suguna K. Structural basis for carbohydrate specificity of basic winged bean lectin. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305088689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Vijayan M, Saikrishnan K, Kumar P, Dauter Z, Sekar K, Surolia A, Singh DD. Banana lectin, a β-prism I fold lectin with two carbohydrate-binding sites. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305090094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Singh DD, Saikrishnan K, Kumar P, Surolia A, Sekar K, Vijayan M. Unusual sugar specificity of banana lectin from Musa paradisiaca and its probable evolutionary origin. Crystallographic and modelling studies. Glycobiology 2005; 15:1025-32. [PMID: 15958419 DOI: 10.1093/glycob/cwi087] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The crystal structure of a complex of methyl-alpha-D-mannoside with banana lectin from Musa paradisiaca reveals two primary binding sites in the lectin, unlike in other lectins with beta-prism I fold which essentially consists of three Greek key motifs. It has been suggested that the fold evolved through successive gene duplication and fusion of an ancestral Greek key motif. In other lectins, all from dicots, the primary binding site exists on one of the three motifs in the three-fold symmetric molecule. Banana is a monocot, and the three motifs have not diverged enough to obliterate sequence similarity among them. Two Greek key motifs in it carry one primary binding site each. A common secondary binding site exists on the third Greek key. Modelling shows that both the primary sites can support 1-2, 1-3, and 1-6 linked mannosides with the second residue interacting in each case primarily with the secondary binding site. Modelling also readily leads to a bound branched mannopentose with the nonreducing ends of the two branches anchored at the two primary binding sites, providing a structural explanation for the lectin's specificity for branched alpha-mannans. A comparison of the dimeric banana lectin with other beta-prism I fold lectins, provides interesting insights into the variability in their quaternary structure.
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Affiliation(s)
- D D Singh
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, Karnataka, India
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Suresh S, Rani PG, Pratap JV, Sankaranarayana R, Surolia A, Vijayan M. Homology between jacalin and artocarpin from jackfruit (Artocarpus integrifolia) seeds. Partial sequence and preliminary crystallographic studies of artocarpin. Acta Crystallogr D Biol Crystallogr 2005; 53:469-71. [PMID: 15299916 DOI: 10.1107/s0907444997000851] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Jacalin and artocarpin, the two lectins from jackfruit (Artocarpus integrifolia) seeds, have different physicochemical properties and carbohydrate-binding specificities. However, comparison of the partial amino-acid sequence of artocarpin with the known sequence of jacalin indicates close to 50% sequence identity. Artocarpin crystallizes in two forms, both monoclinic P2(1), with one and two tetramic molecules, respectively, in the asymmetric units of form I (a = 69.9, b = 73.7, c = 60.6 A and beta = 95.1 degrees ) and form II (a = 87.6, b = 72.2, c = 92.6 A and beta = 101.1 degrees ). Both the crystal structures have been solved by the molecular replacement method using the known structure of jacalin as the search model and one of them partially refined, confirming that the two lectins are indeed homologous.
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Affiliation(s)
- S Suresh
- Molecular Biophyiscs Unit, Indian Institute of Science, Bangalore, India
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20
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Arockia Jeyaprakash A, Jayashree G, Mahanta SK, Swaminathan CP, Sekar K, Surolia A, Vijayan M. Structural basis for the energetics of jacalin-sugar interactions: promiscuity versus specificity. J Mol Biol 2005; 347:181-8. [PMID: 15733927 DOI: 10.1016/j.jmb.2005.01.015] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Revised: 12/29/2004] [Accepted: 01/05/2005] [Indexed: 11/21/2022]
Abstract
Jacalin, a tetrameric lectin, is one of the two lectins present in jackfruit (Artocarpus integrifolia) seeds. Its crystal structure revealed, for the first time, the occurrence of the beta-prism I fold in lectins. The structure led to the elucidation of the crucial role of a new N terminus generated by post-translational proteolysis for the lectin's specificity for galactose. Subsequent X-ray studies on other carbohydrate complexes showed that the extended binding site of jacalin consisted of, in addition to the primary binding site, a hydrophobic secondary site A composed of aromatic residues and a secondary site B involved mainly in water-bridges. A recent investigation involving surface plasmon resonance and the X-ray analysis of a methyl-alpha-mannose complex, had led to a suggestion of promiscuity in the lectin's sugar specificity. To explore this suggestion further, detailed isothermal titration calorimetric studies on the interaction of galactose (Gal), mannose (Man), glucose (Glc), Me-alpha-Gal, Me-alpha-Man, Me-alpha-Glc and other mono- and oligosaccharides of biological relevance and crystallographic studies on the jacalin-Me-alpha-Glc complex and a new form of the jacalin-Me-alpha-Man complex, have been carried out. The binding affinity of Me-alpha-Man is 20 times weaker than that of Me-alpha-Gal. The corresponding number is 27, when the binding affinities of Gal and Me-alpha-Gal, and those of Man and Me-alpha-Man are compared. Glucose (Glc) shows no measurable binding, while the binding affinity of Me-alpha-Glc is slightly less than that of Me-alpha-Man. The available crystal structures of jacalin-sugar complexes provide a convincing explanation for the energetics of binding in terms of interactions at the primary binding site and secondary site A. The other sugars used in calorimetric studies show no detectable binding to jacalin. These results and other available evidence suggest that jacalin is specific to O-glycans and its affinity to N-glycans is extremely weak or non-existent and therefore of limited value in processes involving biological recognition.
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Das S, Kumar P, Bhor V, Surolia A, Vijayan M. Expression, purification, crystallization and preliminary X-ray crystallographic analysis of pantothenate kinase from Mycobacterium tuberculosis. Acta Crystallogr Sect F Struct Biol Cryst Commun 2005; 61:65-7. [PMID: 16508093 PMCID: PMC1952411 DOI: 10.1107/s1744309104028040] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2004] [Accepted: 11/01/2004] [Indexed: 11/10/2022]
Abstract
Pantothenate kinase is an essential enzyme in the bacterial life cycle. It catalyzes the phosphorylation of pantothenate (vitamin B5) to 4'-phosphopantothenate, the first step in the coenzyme A biosynthetic pathway. The enzyme from Mycobacterium tuberculosis, MW 35.7 kDa, has been cloned, expressed, purified and crystallized in two different trigonal crystal forms, both belonging to space group P3(1)21. Two complete data sets of resolution 2.5 A (form I) and 2.9 A (form II) from crystals with unit-cell parameters a = b = 78.3, c = 115.45 A and a = b = 107.63, c = 89.85 A, respectively, were collected at room temperature on a home X-ray source. Structures of both crystal forms were solved for one subunit in the asymmetric unit by molecular replacement.
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Affiliation(s)
- Satyabrata Das
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - Parimal Kumar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - Vikrant Bhor
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - A. Surolia
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
| | - M. Vijayan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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22
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Kulkarni KA, Srivastava A, Mitra N, Sharon N, Surolia A, Vijayan M, Suguna K. Effect of glycosylation on the structure of Erythrina corallodendron lectin. Proteins 2004; 56:821-7. [PMID: 15281133 DOI: 10.1002/prot.20168] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The three-dimensional structure of the recombinant form of Erythrina corallodendron lectin, complexed with lactose, has been elucidated by X-ray crystallography at 2.55 A resolution. Comparison of this non-glycosylated structure with that of the native glycosylated lectin reveals that the tertiary and quaternary structures are identical in the two forms, with local changes observed at one of the glycosylation sites (Asn17). These changes take place in such a way that hydrogen bonds with the neighboring protein molecules in rECorL compensate those made by the glycan with the protein in ECorL. Contrary to an earlier report, this study demonstrates that the glycan attached to the lectin does not influence the oligomeric state of the lectin. Identical interactions between the lectin and the non-covalently bound lactose in the two forms indicate, in line with earlier reports, that glycosylation does not affect the carbohydrate specificity of the lectin. The present study, the first of its kind involving a glycosylated protein with a well-defined glycan and the corresponding deglycosylated form, provides insights into the structural aspects of protein glycosylation.
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Affiliation(s)
- K A Kulkarni
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Singh DD, Saikrishnan K, Kumar P, Dauter Z, Sekar K, Surolia A, Vijayan M. Purification, crystallization and preliminary X-ray structure analysis of the banana lectin fromMusa paradisiaca. Acta Crystallogr D Biol Crystallogr 2004; 60:2104-6. [PMID: 15502341 DOI: 10.1107/s0907444904024114] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2004] [Accepted: 09/25/2004] [Indexed: 05/01/2023]
Abstract
The banana lectin from Musa paradisiaca, MW 29.4 kDa, has been isolated, purified and crystallized. The trigonal crystals contain one dimeric molecule in the asymmetric unit. The structure has been solved using molecular replacement to a resolution of 3 A. The structure of the subunit is similar to that of jacalin-like lectins.
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Affiliation(s)
- D D Singh
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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Jeyaprakash AA, Srivastav A, Surolia A, Vijayan M. Structural Basis for the Carbohydrate Specificities of Artocarpin: Variation in the Length of a Loop as a Strategy for Generating Ligand Specificity. J Mol Biol 2004; 338:757-70. [PMID: 15099743 DOI: 10.1016/j.jmb.2004.03.040] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Revised: 03/05/2004] [Accepted: 03/10/2004] [Indexed: 11/18/2022]
Abstract
Artocarpin, a tetrameric lectin of molecular mass 65 kDa, is one of the two lectins extracted from the seeds of jackfruit. The structures of the complexes of artocarpin with mannotriose and mannopentose reported here, together with the structures of artocarpin and its complex with Me-alpha-mannose reported earlier, show that the lectin possesses a deep-seated binding site formed by three loops. The binding site can be considered as composed of two subsites; the primary site and the secondary site. Interactions at the primary site composed of two of the loops involve mainly hydrogen bonds, while those at the secondary site comprising the third loop are primarily van der Waals in nature. Mannotriose in its complex with the lectin interacts through all the three mannopyranosyl residues; mannopentose interacts with the protein using at least three of the five mannose residues. The complexes provide a structural explanation for the carbohydrate specificities of artocarpin. A detailed comparison with the sugar complexes of heltuba, the only other mannose-specific jacalin-like lectin with known three-dimensional structure in sugar-bound form, establishes the role of the sugar-binding loop constituting the secondary site, in conferring different specificities at the oligosaccharide level. This loop is four residues longer in artocarpin than in heltuba, providing an instance where variation in loop length is used as a strategy for generating carbohydrate specificity.
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Kundhavai Natchiar S, Arockia Jeyaprakash A, Ramya TNC, Thomas CJ, Suguna K, Surolia A, Vijayan M. Structural plasticity of peanut lectin: an X-ray analysis involving variation in pH, ligand binding and crystal structure. Acta Crystallogr D Biol Crystallogr 2004; 60:211-9. [PMID: 14747696 DOI: 10.1107/s090744490302849x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2003] [Accepted: 12/08/2003] [Indexed: 11/10/2022]
Abstract
Until recently, it has only been possible to grow crystals of peanut lectin when complexed with sugar ligands. It is now shown that it is possible to grow peanut lectin crystals at acidic pH in the presence of oligopeptides corresponding to a loop in the lectin molecule. Crystals have also been prepared in the presence of these peptides as well as lactose. Low-pH crystal forms of the lectin-lactose complex similar to those obtained at neutral pH have also been grown. Thus, crystals of peanut lectin grown under different environmental conditions, at two pH values with and without sugar bound to the lectin, are now available. They have been used to explore the plasticity and hydration of the molecule. A detailed comparison between different structures shows that the lectin molecule is sturdy and that the effect of changes in pH, ligand binding and environment on it is small. The region involving the curved front beta-sheet and the loops around the second hydrophobic core is comparatively rigid. The back beta-sheet involved in quaternary association, which exhibits considerable variability, is substantially flexible, as is the sugar-binding region. The numbers of invariant water molecules in the hydration shell are small and they are mainly involved in metal coordination or in stabilizing unusual structural features. Small consistent movements occur in the combining site upon sugar binding, although the site is essentially preformed.
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Affiliation(s)
- S Kundhavai Natchiar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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26
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Ramachandraiah G, Chandra NR, Surolia A, Vijayan M. Computational analysis of multivalency in lectins: structures of garlic lectin-oligosaccharide complexes and their aggregates. Glycobiology 2003; 13:765-75. [PMID: 12851290 DOI: 10.1093/glycob/cwg095] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Multivalency in lectins is a phenomenon that has been discussed at considerable length. The structural basis for the role of multivalency in garlic lectin has been investigated here through computational studies. Biochemical studies have shown that the binding affinity of garlic lectin for high mannose oligosaccharides is orders of magnitude greater than that for mannose. Modeling and energy calculations clearly indicate that such increase in affinity cannot be accounted for by binding of these oligosaccharides at any of the six sites of a garlic lectin dimer. These studies also indicate that a given oligosaccharide cannot bind simultaneously to more than one binding site on a lectin dimer. The possibility of a given oligosaccharide simultaneously binding to and hence linking two or more lectin molecules was therefore explored. This study showed that trimannosides and higher oligomers can cross-link lectin dimers, amplifying the protein-oligosaccharide interactions severalfold, thus explaining the role of multivalency in enhancing affinity. A comprehensive exploration of all possible cross-links posed a formidable computational problem. Even a partial exploration involving a carefully chosen region of the conformational space clearly showed that a given dimer pair can be cross-linked not only by a single oligosaccharide molecule but also simultaneously by two oligosaccharides. The number of such possible double cross-links, including those forming interesting tetrameric structures, generally increases with the size of the oligosaccharide, correlating with the biochemical data. In addition to their immediate relevance to garlic lectin, these studies are of general interest in relation to lectin-oligosaccharide interactions.
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Affiliation(s)
- Gosu Ramachandraiah
- Molecular Biophysics Unit, Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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27
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Jeyaprakash AA, Katiyar S, Swaminathan CP, Sekar K, Surolia A, Vijayan M. Structural basis of the carbohydrate specificities of jacalin: an X-ray and modeling study. J Mol Biol 2003; 332:217-28. [PMID: 12946359 DOI: 10.1016/s0022-2836(03)00901-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The structures of the complexes of tetrameric jacalin with Gal, Me-alpha-GalNAc, Me-alpha-T-antigen, GalNAcbeta1-3Gal-alpha-O-Me and Galalpha1-6Glc (mellibiose) show that the sugar-binding site of jacalin has three components: the primary site, secondary site A, and secondary site B. In these structures and in the two structures reported earlier, Gal or GalNAc occupy the primary site with the anomeric carbon pointing towards secondary site A. The alpha-substituents, when present, interact, primarily hydrophobically, with secondary site A which has variable geometry. O-H..., centered pi and C-H...pi hydrogen bonds involving this site also exist. On the other hand, beta-substitution leads to severe steric clashes. Therefore, in complexes involving beta-linked disaccharides, the reducing sugar binds at the primary site with the non-reducing end located at secondary site B. The interactions at secondary site B are primarily through water bridges. Thus, the nature of the linkage determines the mode of the association of the sugar with jacalin. The interactions observed in the crystal structures and modeling based on them provide a satisfactory qualitative explanation of the available thermodynamic data on jacalin-carbohydrate interactions. They also lead to fresh insights into the nature of the binding of glycoproteins by jacalin.
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Affiliation(s)
- A Arockia Jeyaprakash
- Molecular Biophysics Unit, UGC Centre of Advanced Study, Indian Institute of Science, Bangalore 560 012, India
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28
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Ramesh J, Ghosh JK, Swaminathan CP, Ramasamy P, Surolia A, Sikdar SK, Easwaran KRK. Studies on the aggregation and possible channel formation in membranes of a cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2. J Pept Res 2003; 61:63-70. [PMID: 12492900 DOI: 10.1034/j.1399-3011.2003.00033.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The interaction of zwitterionic lipid DMPC and DPPC with cyclic hexapeptide, cyclo (D-Ala-L-Pro-L-Ala)2 was studied using circular dichroism (CD) and differential scanning calorimetry (DSC). Preliminary membrane conductance results showed that the peptide has a tendency to form channels inside the lipid bilayer. CD studies indicated that as the lipid/peptide (L/P) ratio (DMPC/peptide) was increased, the magnitude of the negative CD band having a lambda(max) around 200 nm decreased. At a L/P ratio of 210:1, this band disappeared completely, indicating dramatic conformational changes in the peptide on interaction with the lipid bilayer. Reduction of the phase transition temperature and the maximum heat capacity of the lipid bilayer (DPPC) for gel-to-liquid crystalline phase transition indicates a strong interaction of the peptide with the lipid bilayer.
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Affiliation(s)
- J Ramesh
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Affiliation(s)
- P R Satish
- Division of Nephrology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA, USA
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Jeyaprakash AA, Geetha Rani P, Banuprakash Reddy G, Banumathi S, Betzel C, Sekar K, Surolia A, Vijayan M. Crystal structure of the jacalin-T-antigen complex and a comparative study of lectin-T-antigen complexes. J Mol Biol 2002; 321:637-45. [PMID: 12206779 DOI: 10.1016/s0022-2836(02)00674-5] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Thomsen-Friedenreich antigen (Galbeta1-3GalNAc), generally known as T-antigen, is expressed in more than 85% of human carcinomas. Therefore, proteins which specifically bind T-antigen have potential diagnostic value. Jacalin, a lectin from jack fruit (Artocarpus integrifolia) seeds, is a tetramer of molecular mass 66kDa. It is one of the very few proteins which are known to bind T-antigen. The crystal structure of the jacalin-T-antigen complex has been determined at 1.62A resolution. The interactions of the disaccharide at the binding site are predominantly through the GalNAc moiety, with Gal interacting only through water molecules. They include a hydrogen bond between the anomeric oxygen of GalNAc and the pi electrons of an aromatic side-chain. Several intermolecular interactions involving the bound carbohydrate contribute to the stability of the crystal structure. The present structure, along with that of the Me-alpha-Gal complex, provides a reasonable qualitative explanation for the known affinities of jacalin to different carbohydrate ligands and a plausible model of the binding of the lectin to T-antigen O-linked to seryl or threonyl residues. Including the present one, the structures of five lectin-T-antigen complexes are available. GalNAc occupies the primary binding site in three of them, while Gal occupies the site in two. The choice appears to be related to the ability of the lectin to bind sialylated sugars. In either case, most of the lectin-disaccharide interactions are at the primary binding site. The conformation of T-antigen in the five complexes is nearly the same.
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Affiliation(s)
- A Arockia Jeyaprakash
- Molecular Biophysics Unit, Indian Institute of Science, UGC Centre of Advanced Science, Bangalore, India
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Pratap JV, Jeyaprakash AA, Rani PG, Sekar K, Surolia A, Vijayan M. Crystal structures of artocarpin, a Moraceae lectin with mannose specificity, and its complex with methyl-alpha-D-mannose: implications to the generation of carbohydrate specificity. J Mol Biol 2002; 317:237-47. [PMID: 11902840 DOI: 10.1006/jmbi.2001.5432] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The seeds of jack fruit (Artocarpus integrifolia) contain two tetrameric lectins, jacalin and artocarpin. Jacalin was the first lectin found to exhibit the beta-prism I fold, which is characteristic of the Moraceae plant lectin family. Jacalin contains two polypeptide chains produced by a post-translational proteolysis which has been shown to be crucial for generating its specificity for galactose. Artocarpin is a single chain protein with considerable sequence similarity with jacalin. It, however, exhibits many properties different from those of jacalin. In particular, it is specific to mannose. The structures of two crystal forms, form I and form II, of the native lectin have been determined at 2.4 and 2.5 A resolution, respectively. The structure of the lectin complexed with methyl-alpha-mannose, has also been determined at 2.9 A resolution. The structure is similar to jacalin, although differences exist in details. The crystal structures and detailed modelling studies indicate that the following differences between the carbohydrate binding sites of artocarpin and jacalin are responsible for the difference in the specificities of the two lectins. Firstly, artocarpin does not contain, unlike jacalin, an N terminus generated by post-translational proteolysis. Secondly, there is no aromatic residue in the binding site of artocarpin whereas there are four in that of jacalin. A comparison with similar lectins of known structures or sequences, suggests that, in general, stacking interactions with aromatic residues are important for the binding of galactose while such interactions are usually absent in the carbohydrate binding sites of mannose-specific lectins with the beta-prism I fold.
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Affiliation(s)
- J V Pratap
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Ramachandraiah G, Chandra NR, Surolia A, Vijayan M. Re-refinement using reprocessed data to improve the quality of the structure: a case study involving garlic lectin. Acta Crystallogr D Biol Crystallogr 2002; 58:414-20. [PMID: 11856826 DOI: 10.1107/s0907444901021497] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2001] [Accepted: 12/13/2001] [Indexed: 11/10/2022]
Abstract
The structure of dimeric garlic lectin was previously determined to an effective resolution of 2.8A using X-ray intensity data processed by the XDS package and refined using X-PLOR [Chandra et al. (1999), J. Mol. Biol. 285, 1157--1168]. Repeated attempts to grow better crystals with a view to improving the definition of the structure did not succeed. The available raw data were then reprocessed using DENZO. The structure was re-refined with both X-PLOR and CNS separately using the reprocessed data, which extended to a resolution of 2.2A. These two sets of refinements and the two sets using the XDS-processed data afforded an opportunity to compare the performance of different data-processing and refinement packages when dealing with data from weakly diffracting crystals. The best results were obtained when CNS was employed for refinement using data processed by DENZO. The quality and the resolution of the map and the definition of the structure improved substantially. In particular, the amino-acid residues at the variable locations in the sequence, and hence the isolectins, could be identified with a high degree of confidence. It could be established that the crystal asymmetric unit contains two identical heterodimers. The new refined structure also provided a better definition of other finer structural details.
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Affiliation(s)
- Gosu Ramachandraiah
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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33
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Kapoor M, Dar MJ, Surolia A, Surolia N. Kinetic determinants of the interaction of enoyl-ACP reductase from Plasmodium falciparum with its substrates and inhibitors. Biochem Biophys Res Commun 2001; 289:832-7. [PMID: 11735121 DOI: 10.1006/bbrc.2001.6061] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have recently demonstrated that Plasmodium falciparum, unlike its human host, has the type II fatty acid synthase, in which steps of fatty acid biosynthesis are catalyzed by independent enzymes. This difference could be successfully exploited in the design of drugs specifically targeted at the different enzymes of this pathway in P. falciparum, without affecting the corresponding enzymes in humans. The importance of enoyl-ACP reductase (FabI) in the fatty acid biosynthesis pathway makes it an important target in antimalarial therapy. We report here the initial characterization of Plasmodium FabI expressed in Escherichia coli. The K(m) values of the enzyme for crotonyl-CoA and NADH were derived as 165 and 33 microM, respectively. Triclosan shows competitive kinetics with respect to NADH but is uncompetitive with respect to NAD(+), which shows that the binding of triclosan to the enzyme is facilitated in the presence of NAD(+).
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Affiliation(s)
- M Kapoor
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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Moorthy AK, Singh SK, Gopal B, Surolia A, Murthy MR. Variability of calcium binding to EF-hand motifs probed by electrospray ionization mass spectrometry. J Am Soc Mass Spectrom 2001; 12:1296-1301. [PMID: 11766756 DOI: 10.1016/s1044-0305(01)00317-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The modulation of calcium binding by the EF-hand motifs present in a calmodulin (CAM) homologue, a calcium binding protein (CaBP) from Entamoeba histolytica by three external parameters-pH, ligand coordinator EGTA, and fragmentor voltage was investigated by mass spectrometry. Calcium binding follows expected patterns at highly acidic and alkaline pH with the preponderance of the apo and the completely saturated forms, respectively. Surprisingly, additional nonspecific binding is observed near neutral pH. Studies on EGTA chelation and effects of fragmentor voltage showed cooperativity in calcium removal in at least one of the domains. Similar studies on a smaller construct containing the two high affinity carboxy terminal sites revealed interesting differences and provided an estimate of the specificity and tolerance of the EF-hand motifs to calcium binding and removal.
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Affiliation(s)
- A K Moorthy
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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35
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Salunke D, Khan M, Surolia A, Vijayan M. Preparation and preliminary X-ray studies of three acidic pH crystal forms of the anti-T lectin from peanut (Arachis hypogaea
). FEBS Lett 2001. [DOI: 10.1016/0014-5793(83)80262-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Adhikari P, Bachhawat-Sikder K, Thomas CJ, Ravishankar R, Jeyaprakash AA, Sharma V, Vijayan M, Surolia A. Mutational analysis at Asn-41 in peanut agglutinin. A residue critical for the binding of the tumor-associated Thomsen-Friedenreich antigen. J Biol Chem 2001; 276:40734-9. [PMID: 11447220 DOI: 10.1074/jbc.m103040200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Peanut agglutinin is a clinically important lectin due to its application in the screening of mature and immature thymocytes as well as in the detection of cancerous malignancies. The basis for these applications is the remarkably strong affinity of the lectin for the tumor-associated Thomsen-Friedenreich antigen (T-antigen) and more so due to its ability to distinguish T-antigen from its cryptic forms. The crystal structure of the complex of peanut agglutinin with T-antigen reveals the basis of this specificity. Among the contacts involved in providing this specificity toward T-antigen is the water-mediated interaction between the side chain of Asn-41 and the carbonyl oxygen of the acetamido group of the second hexopyranose ring of the sugar molecule. Site-directed mutational changes were introduced at this residue with the objective of probing the role of this residue in T-antigen binding and possibly engineering an altered species with increased specificity for T-antigen. Of the three mutants tested, i.e. N41A, N41D, and N41Q, the last one shows improved potency for recognition of T-antigen. The affinities of the mutants can be readily explained on the basis of the crystal structure of the complex and simple modeling. In particular, the change of asparagine to glutamine could lead to a direct interaction of the side chain with the sugar while at the same time retaining the water bridge. This study strengthens the theory that in lectins the nonprimary contacts generally made through water bridges are involved in imparting exquisite specificity.
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Affiliation(s)
- P Adhikari
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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37
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Pratap JV, Bradbrook GM, Reddy GB, Surolia A, Raftery J, Helliwell JR, Vijayan M. The combination of molecular dynamics with crystallography for elucidating protein-ligand interactions: a case study involving peanut lectin complexes with T-antigen and lactose. Acta Crystallogr D Biol Crystallogr 2001; 57:1584-94. [PMID: 11679723 DOI: 10.1107/s0907444901011957] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2001] [Accepted: 07/16/2001] [Indexed: 11/11/2022]
Abstract
Peanut lectin binds T-antigen [Galbeta(1-3)GalNAc] with an order of magnitude higher affinity than it binds the disaccharide lactose. The crystal structures of the two complexes indicate that the higher affinity for T-antigen is generated by two water bridges involving the acetamido group. Fresh calorimetric measurements on the two complexes have been carried out in the temperature range 280-313 K. Four sets of nanosecond molecular-dynamics (MD) simulations, two at 293 K and the other two at 313 K, were performed on each of the two complexes. At each temperature, two somewhat different protocols were used to hydrate the complex in the two runs. Two MD runs under slightly different conditions for each complex served to assess the reliability of the approach for exploring protein-ligand interactions. Enthalpies based on static calculations and on MD simulations favour complexation involving T-antigen. The simulations also brought to light ensembles of direct and water-mediated protein-sugar interactions in both the cases. These ensembles provide a qualitative explanation for the temperature dependence of the thermodynamic parameters of peanut lectin-T-antigen interaction and for the results of one of the two mutational studies on the lectin. They also support the earlier conclusion that the increased affinity of peanut lectin for T-antigen compared with that for lactose is primarily caused by additional water bridges involving the acetamido group. The calculations provide a rationale for the observed sugar-binding affinity of one of the two available mutants. Detailed examination of the calculations point to the need for exercising caution in interpreting results of MD simulations: while long simulations are not possible owing to computational reasons, it is desirable to carry out several short simulations with somewhat different initial conditions.
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Affiliation(s)
- J V Pratap
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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38
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Abstract
Many naturally occurring peptides exhibit lipopolysaccharide binding properties. In this work we describe the endotoxin binding properties of a series of 23-residue peptides based on the sequence corresponding to the antisense strand of the magainin gene. Biochemical and biophysical characterization of these peptides reveals that they have the tendency to perturb both the inner and outer membranes of test pathogens. Structurally these peptides are amphiphilic and adopt helical conformations in membranes. Three of the seven peptides tested have high affinities for endotoxin that approach the values shown by polymyxin B, a cyclic cationic acylated decapeptide, which is used clinically in treating extreme cases of sepsis. The kinetic parameters obtained using stopped-flow methods and BIAcore analysis, when considered in conjunction with the isothermal titration calorimetry-derived thermodynamic parameters, allow us to highlight the key structural features essential for lipopolysaccharide (LPS) recognition by these peptides. The studies stress the role of ionic forces in the initial recognition of LPS. The fortification of the strength of these ionic charges increases affinity for LPS, whereas the hydrophobic residues involved in interactions are more amenable to disruptions in contiguity. Peptides that improve these features further are expected to perform better as endotoxin-neutralizing agents.
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Affiliation(s)
- C J Thomas
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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39
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Srinivas VR, Reddy GB, Ahmad N, Swaminathan CP, Mitra N, Surolia A. Legume lectin family, the 'natural mutants of the quaternary state', provide insights into the relationship between protein stability and oligomerization. Biochim Biophys Acta 2001; 1527:102-11. [PMID: 11479026 DOI: 10.1016/s0304-4165(01)00153-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Legume lectins family of proteins, despite having the same 'jelly roll' tertiary structural fold at monomeric level, exhibit considerable variation in their quaternary structure arising out of small changes in their sequence. Nevertheless, their folding behavior and stability correlates very well with their patterns of assembly into dimers and tetramers. A conservation of their fold during evolution, its wide distribution in many protein families together with the availability of structural information on them make them interesting as proteins to explore the effect of inter- versus intra-subunit interactions in the stability of multimeric proteins. Additionally, as 'natural mutants' of quaternary association, proteins of legume lectin family provide interesting paradigms for studies addressing the effect of subunit oligomerization on the stability, folding and function as well as the evolution of multimeric structures.
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Affiliation(s)
- V R Srinivas
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012
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40
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Abstract
Galectin-3, with a wide tissue distribution and marked developmental regulation, provides significant insights into the progression of various disease and developmental stages. Recognized by its specificity for galactose, a detailed characterization of its sugar binding ability has been investigated by isothermal titration calorimetry. The results presented here complement well with the earlier studies utilizing hapten inhibition assays. Among the various lactose derivatives studied, A-tetrasaccharide emerged with the highest affinity for binding to galectin-3 combining site. This blood group saccharide exhibited a binding affinity 37-fold higher and a 102 kJ/mol more favorable change in enthalpy over lactose at 280 K indicating the existence of additional subsites for both the alpha1-3-linked N-acetylgalactosamine at the non-reducing end and the alpha1-2-linked L-fucosyl residue. The thermodynamic parameters evaluated for other ligands substantiate further the carbohydrate recognition domain to be part of an extended binding site. Binding thermodynamics of galectin-3 with the galactose derivatives are essentially enthalpically driven and exhibit compensatory changes in DeltaH degrees and TDeltaS owing to solvent reorganization.
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Affiliation(s)
- K Bachhawat-Sikder
- Molecular Bioiphysics Unit, Indian Institute of Science, Bangalore 560012, India
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41
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Bachhawat K, Kapoor M, Dam TK, Surolia A. The reversible two-state unfolding of a monocot mannose-binding lectin from garlic bulbs reveals the dominant role of the dimeric interface in its stabilization. Biochemistry 2001; 40:7291-300. [PMID: 11401577 DOI: 10.1021/bi0027783] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Allium sativum agglutinin (ASAI) is a heterodimeric mannose-specific bulb lectin possessing two polypeptide chains of molecular mass 11.5 and 12.5 kDa. The thermal unfolding of ASAI, characterized by differential scanning calorimetry and circular dichroism, shows it to be highly reversible and can be defined as a two-state process in which the folded dimer is converted directly to the unfolded monomers (A2 if 2U). Its conformational stability has been determined as a function of temperature, GdnCl concentration, and pH using a combination of thermal and isothermal GdnCl-induced unfolding monitored by DSC, far-UV CD, and fluorescence, respectively. Analyses of these data yielded the heat capacity change upon unfolding (DeltaC(p) and also the temperature dependence of the thermodynamic parameters, namely, DeltaG, DeltaH, and DeltaS. The fit of the stability curve to the modified Gibbs-Helmholtz equation provides an estimate of the thermodynamic parameters DeltaH(g), DeltaS(g), and DeltaC(p) as 174.1 kcal x mol(-1), 0.512 kcal x mol(-1) x K(-1), and 3.41 kcal x mol(-1) x K(-1), respectively, at T(g) = 339.4 K. Also, the free energy of unfolding, DeltaG(s), at its temperature of maximum stability (T(s) = 293 K) is 13.13 kcal x mol(-1). Unlike most oligomeric proteins studied so far, the lectin shows excellent agreement between the experimentally determined DeltaC(p) (3.2 +/- 0.28 kcal x mol(-1) x K(-1)) and those evaluated from a calculation of its accessible surface area. This in turn suggests that the protein attains a completely unfolded state irrespective of the method of denaturation. The absence of any folding intermediates suggests the quaternary interactions to be the major contributor to the conformational stability of the protein, which correlates well with its X-ray structure. The small DeltaC(p) for the unfolding of ASAI reflects a relatively small, buried hydrophobic core in the folded dimeric protein.
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Affiliation(s)
- K Bachhawat
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore-560012, India.
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42
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Srinivas VR, Bachhawat-Sikder K, Habib S, Hasnain SE, Surolia A. Expression of winged bean basic agglutinin in Spodoptera frugiperda insect cell expression system. Biosci Rep 2001; 21:361-7. [PMID: 11893002 DOI: 10.1023/a:1013294417847] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this paper we report the successful expression of the winged bean basic agglutinin (WBA I) in insect cells infected with a recombinant baculovirus carrying the WBA I gene and its characterization in terms of its carbohydrate binding properties. The expressed protein appears to have a lower molecular weight than the native counterpart which is consistent with the lack of glycosylation of the former. Moreover, the expressed protein maintains its dimeric nature. Hence, a role for glycosylation in modulation of dimerization of WBA I is ruled out unlike Erythrina corallodendron (EcorL). Despite this the protein is active, with its sugar specificity unaltered.
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Affiliation(s)
- V R Srinivas
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore
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43
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Ravishankar R, Thomas CJ, Suguna K, Surolia A, Vijayan M. Crystal structures of the peanut lectin-lactose complex at acidic pH: retention of unusual quaternary structure, empty and carbohydrate bound combining sites, molecular mimicry and crystal packing directed by interactions at the combining site. Proteins 2001; 43:260-70. [PMID: 11288176 DOI: 10.1002/prot.1037] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The crystal structures of a monoclinic and a triclinic form of the peanut lectin-lactose complex, grown at pH 4.6, have been determined. They contain two and one crystallographically independent tetramers, respectively. The unusual "open" quaternary structure of the lectin, observed in the orthorhombic complex grown in neutral pH, is retained at the acidic pH. The sugar molecule is bound to three of the eight subunits in the monoclinic crystals, whereas the combining sites in four are empty. The lectin-sugar interactions are almost the same at neutral and acidic pH. A comparison of the sugar-bound and free subunits indicates that the geometry of the combining site is relatively unaffected by ligand binding. The combining site of the eighth subunit in the monoclinic crystals is bound to a peptide stretch in a loop from a neighboring molecule. The same interaction exists in two subunits of the triclinic crystals, whereas density corresponding to sugar exists in the combining sites of the other two subunits. Solution studies show that oligopeptides with sequences corresponding to that in the loop bind to the lectin at acidic pH, but only with reduced affinity at neutral pH. The reverse is the case with the binding of lactose to the lectin. A comparison of the neutral and acidic pH crystal structures indicates that the molecular packing in the latter is directed to a substantial extent by the increased affinity of the peptide loop to the combining site at acidic pH.
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Affiliation(s)
- R Ravishankar
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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44
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Abstract
Recent discovery of type II fatty acid synthase in the malarial parasite Plasmodium falciparum responsible for the most debilitating form of the disease in humans makes it ideal as a target for the development of novel antimalarials. Also, the identification of the enoyl-acyl carrier protein reductase from P. falciparum and the demonstration of its inhibition by triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol], a potent antibacterial compound, provide strong support for the above. In the studies reported here, a model of the enzyme in complex with triclosan and the cofactor NAD has been built by homology modeling with a view to understand its binding properties and to explore the potential of triclosan as a lead compound in designing effective antimalarial drugs. The model indeed provided the structural rationale for its interaction with ligands and the cofactor and revealed unique characteristics of its binding site which could be exploited for improving the specificity of the inhibitors.
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Affiliation(s)
- K Suguna
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560 012, India
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45
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Bachhawat K, Thomas CJ, Amutha B, Krishnasastry MV, Khan MI, Surolia A. On the stringent requirement of mannosyl substitution in mannooligosaccharides for the recognition by garlic (Allium sativum) lectin. A Surface Plasmon Resonance Study. J Biol Chem 2001; 276:5541-6. [PMID: 11076955 DOI: 10.1074/jbc.m009533200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The kinetics of the binding of mannooligosaccharides to the heterodimeric lectin from garlic bulbs was studied using surface plasmon resonance. The interaction of the bound lectin immobilized on the sensor chip with a selected group of high mannose oligosaccharides was monitored in real time with the change in response units. This investigation corroborates our earlier study about the special preference of garlic lectin for terminal alpha-1,2-linked mannose residues. An increase in binding propensity can be directly correlated to the addition of alpha-1,2-linked mannose to the mannooligosaccharide at its nonreducing end. Mannononase glycopeptide (Man9GlcNAc2Asn), the highest oligomer studied, exhibited the greatest binding affinity (Ka = 1.2 x 10(6) m(-1) at 25 degrees C). An analysis of these data reveals that the alpha-1,2-linked terminal mannose on the alpha-1,6 arm is the critical determinant in the recognition of mannooligosaccharides by the lectin. The association (k1) and dissociation rate constants (k(-1)) for the binding of Man9GlcNAc2Asn to Allium sativum agglutinin I are 6.1 x 10(4) m(-1) s(-1) and 4.9 x 10(-2) s(-1), respectively, at 25 degrees C. Whereas k1 increases progressively from Man3 to Man7 derivatives, and more dramatically so for Man8 and Man9 derivatives, k(-1) decreases relatively much less gradually from Man3 to Man9 structures. An unprecedented increase in the association rate constant for interaction with Allium sativum agglutinin I with the structure of the oligosaccharide ligand constitutes a significant finding in protein-sugar recognition.
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Affiliation(s)
- K Bachhawat
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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46
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Abstract
The antimicrobial biocide triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol] potently inhibits the growth of Plasmodium falciparum in vitro and, in a mouse model, Plasmodium berghei in vivo. Inhibition of [14C]acetate and [14C]malonyl-CoA incorporation into fatty acids in vivo and in vitro, respectively, by triclosan implicate FabI as its target. Here we demonstrate that the enoyl-ACP reductase purified from P. falciparum is triclosan sensitive. Also, we present the evidence for the existence of FabI gene in P. falciparum. We establish the existence of the de novo fatty acid biosynthetic pathway in this parasite, and identify a key enzyme of this pathway for the development of new antimalarials.
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Affiliation(s)
- N Surolia
- Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, India
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47
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Manoj N, Srinivas VR, Surolia A, Vijayan M, Suguna K. Carbohydrate specificity and salt-bridge mediated conformational change in acidic winged bean agglutinin. J Mol Biol 2000; 302:1129-37. [PMID: 11183779 DOI: 10.1006/jmbi.2000.4111] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Structures of two crystal forms of the dimeric acidic winged bean agglutinin (WBAII) complexed with methyl-alpha-D-galactose have been determined at 3.0 A and 3.3 A resolution. The subunit structure and dimerisation of the lectin are similar to those of the basic lectin from winged bean (WBAI) and the lectin from Erythrina corallodendron (EcorL). The conformation of a loop and its orientation with respect to the rest of the molecule in WBAII are, however, different from those in all the other legume lectins of known structure. This difference appears to have been caused by the formation of two strategically placed salt bridges in the former. Modelling based on the crystal structures provides a rationale for the specificity of the lectin, which is very different from that of WBAI, for the H-antigenic determinant responsible for O blood group reactivity. It also leads to a qualitative explanation for the thermodynamic data on sugar-binding to the lectin, with special emphasis on the role of a tyrosyl residue in the variable loop in the sugar-binding region in generating the carbohydrate specificity of WBAII.
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Affiliation(s)
- N Manoj
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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48
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Bachhawat K, Thomas CJ, Surolia N, Surolia A. Interaction of chloroquine and its analogues with heme: An isothermal titration calorimetric study. Biochem Biophys Res Commun 2000; 276:1075-9. [PMID: 11027592 DOI: 10.1006/bbrc.2000.3592] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Quinoline-containing drugs such as chloroquine and quinine have had a long and successful history in antimalarial chemotherapy. Identification of ferriprotoporphyrin IX ([Fe(III)PPIX], haematin) as the drug receptors for these antimalarials called for investigations of the binding affinity, mode of interaction, and the conditions affecting the interaction. The parameters obtained are significant in recent times with the emergence of chloroquine resistant strains of the malaria parasites. This has underlined the need to unravel the molecular mechanism of their action so as to meet the requirement of an alternative to the existing antimalarial drugs. The isothermal titration calorimetric studies on the interaction of chloroquine with haematin lead us to propose an altered mode of binding. The initial recognition is ionic in nature mediated by the propionyl group of haematin with the quaternary nitrogen on CQ. This ionic interaction induces a conformational change, such as to favour binding of subsequent CQ molecules. On the contrary, conditions emulating the cytosolic environment (pH 7.4 and 150 mM salt) reveal the hydrophobic force to be the sole contributor driving the interaction. Interaction of a carefully selected panel of quinoline antimalarial drugs with monomeric ferriprotoporphyrin IX has also been investigated at pH 5.6 mimicking the acidic environment prevalent in the food vacuoles of parasite, the center of drug activity, which are consistent with their antimalarial activity.
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Affiliation(s)
- K Bachhawat
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore-, 560012, India
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49
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Swaminathan CP, Gupta A, Surolia N, Surolia A. Plasticity in the primary binding site of galactose/N-acetylgalactosamine-specific lectins. Implication of the C-H...O hydrogen bond at the specificity-determining C-4 locus of the saccharide in 4-methoxygalactose recognition by jacalin and winged bean (basic) agglutinin I. J Biol Chem 2000; 275:28483-7. [PMID: 10837488 DOI: 10.1074/jbc.m004685200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is currently believed that an unsubstituted axial hydroxyl at the specificity-determining C-4 locus of galactose is indispensable for recognition by galactose/N-acetylgalactosamine-specific lectins. Titration calorimetry demonstrates that 4-methoxygalactose retains binding allegiance to the Moraceae lectin jacalin and the Leguminosae lectin, winged bean (basic) agglutinin (WBA I). The binding reactions were driven by dominant favorable enthalpic contributions and exhibited significant enthalpy-entropy compensation. Proton NMR titration of 4-methoxygalactose with jacalin and WBA I resulted in broadening of the sugar resonances without any change in chemical shift. The alpha- and beta-anomers of 4-methoxygalactose were found to be in slow exchange with free and lectin-bound states. Both the anomers experience magnetically equivalent environments at the respective binding sites. The binding constants derived from the dependence of NMR line widths on 4-methoxygalactose concentration agreed well with those obtained from titration calorimetry. The results unequivocally demonstrate that the loci corresponding to the axially oriented C-4 hydroxyl group of galactose within the primary binding site of these lectins exhibit plasticity. These analyses suggest, for the first time, the existence of C-H.O-type hydrogen-bond(s) in protein-carbohydrate interactions in general and between the C-4 locus of galactose derivative and the lectins jacalin and WBA I in particular.
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Affiliation(s)
- C P Swaminathan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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50
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Rani PG, Bachhawat K, Reddy GB, Oscarson S, Surolia A. Isothermal titration calorimetric studies on the binding of deoxytrimannoside derivatives with artocarpin: implications for a deep-seated combining site in lectins. Biochemistry 2000; 39:10755-60. [PMID: 10978160 DOI: 10.1021/bi000744p] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The carbohydrate binding specificity of the seed lectin from Artocarpus integrifolia, artocarpin, has been elucidated by the enzyme-linked lectin absorbent assay [Misquith, S., et al (1994) J. Biol. Chem. 269, 30393-30401], wherein it was demonstrated to be a Man/Glc specific lectin with high affinity for the trisaccharide present in the core of all N-linked oligosaccharide chains of glycoproteins. As a consequence of this characterization, the binding epitopes of this trisaccharide, 3, 6-di(alpha-D-mannopyranosyl)-D-mannose, for artocarpin were investigated by isothermal titration calorimetry using its monodeoxy as well as Glc and Gal analogues. The thermodynamic data presented here implicate 2-, 3-, 4-, and 6-hydroxyl groups of the alpha(1-3) Man and alpha(1-6) Man residues, and the 2- and 4-OH groups of the central Man residue, in binding to artocarpin. Nevertheless, alpha(1-3) Man is the primary contributor to the binding affinity, unlike other Man/Glc binding lectins which exhibit a preference for alpha(1-6) Man. In addition, unlike the binding reactions of most lectins reported so far, the interaction of mannotriose involves all of its hydroxyl groups with the combining site of the lectin. Moreover, the free energy and enthalpy contributions to binding of individual hydroxyl groups of the trimannoside estimated from the corresponding monodeoxy analogues show nonlinearity, suggesting differential contributions of the solvent and protein to the thermodynamics of binding of the analogues. Thus, this study not only provides evidence for the extended site recognition of artocarpin for the trimannoside epitope but also suggests that its combining site is best described as a deep cleft as opposed to shallow indentations implicated in other lectins.
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Affiliation(s)
- P G Rani
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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