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Abstract
"Scleroderma," the rheumatologist said after examining my stiff swollen arms and legs. "Unfortunately, given your biomarkers, it's likely to get worse before it gets better, but you never know." She gave a quick rundown of what I might expect-rapidly progressive skin and joint tightening, GI symptoms, high likelihood of multi-organ involvement…. "Let's hope for the best." She paused, then asked if I had any questions.
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2
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Joshi MK, Burton RA, Wu H, Lipchik AM, Craddock BP, Mo H, Parker LL, Miller WT, Post CB. Substrate binding to Src: A new perspective on tyrosine kinase substrate recognition from NMR and molecular dynamics. Protein Sci 2019; 29:350-359. [PMID: 31697410 DOI: 10.1002/pro.3777] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [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: 08/01/2019] [Revised: 11/04/2019] [Accepted: 11/05/2019] [Indexed: 01/01/2023]
Abstract
Most signal transduction pathways in humans are regulated by protein kinases through phosphorylation of their protein substrates. Typical eukaryotic protein kinases are of two major types: those that phosphorylate-specific sequences containing tyrosine (~90 kinases) and those that phosphorylate either serine or threonine (~395 kinases). The highly conserved catalytic domain of protein kinases comprises a smaller N lobe and a larger C lobe separated by a cleft region lined by the activation loop. Prior studies find that protein tyrosine kinases recognize peptide substrates by binding the polypeptide chain along the C-lobe on one side of the activation loop, while serine/threonine kinases bind their substrates in the cleft and on the side of the activation loop opposite to that of the tyrosine kinases. Substrate binding structural studies have been limited to four families of the tyrosine kinase group, and did not include Src tyrosine kinases. We examined peptide-substrate binding to Src using paramagnetic-relaxation-enhancement NMR combined with molecular dynamics simulations. The results suggest Src tyrosine kinase can bind substrate positioning residues C-terminal to the phosphoacceptor residue in an orientation similar to serine/threonine kinases, and unlike other tyrosine kinases. Mutagenesis corroborates this new perspective on tyrosine kinase substrate recognition. Rather than an evolutionary split between tyrosine and serine/threonine kinases, a change in substrate recognition may have occurred within the TK group of the human kinome. Protein tyrosine kinases have long been therapeutic targets, but many marketed drugs have deleterious off-target effects. More accurate knowledge of substrate interactions of tyrosine kinases has the potential for improving drug selectivity.
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Affiliation(s)
- Mehul K Joshi
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana
| | - Robert A Burton
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana.,Ancestry, Lehi, Utah
| | - Heng Wu
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana
| | - Andrew M Lipchik
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana
| | - Barbara P Craddock
- Department of Physiology and Biophysics, School of Medicine, Stony Brook University, Stony Brook, New York
| | - Huaping Mo
- Purdue Interdepartmental NMR Facility PINMRF, Purdue University, West Lafayette, Indiana
| | - Laurie L Parker
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana
| | - W Todd Miller
- Department of Physiology and Biophysics, School of Medicine, Stony Brook University, Stony Brook, New York.,Department of Veterans Affairs Medical Center, Northport, New York
| | - Carol Beth Post
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana
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3
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Burton RA, Chévez JER, Sauerbrey M, Guinovart C, Hartley A, Kirkwood G, Boslego M, Gavidia ME, Alemán Escobar JE, Turkel R, Steketee RW, Slutsker L, Schneider K, Campbell CCK. Factors Associated with the Rapid and Durable Decline in Malaria Incidence in El Salvador, 1980-2017. Am J Trop Med Hyg 2018; 99:33-42. [PMID: 29761766 PMCID: PMC6085812 DOI: 10.4269/ajtmh.17-0629] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
A decade after the Global Malaria Eradication Program, El Salvador had the highest burden of malaria in Mesoamerica, with approximately 20% due to Plasmodium falciparum. A resurgence of malaria in the 1970s led El Salvador to alter its national malaria control strategy. By 1995, El Salvador recorded its last autochthonous P. falciparum case with fewer than 20 Plasmodium vivax cases annually since 2011. By contrast, its immediate neighbors continue to have the highest incidences of malaria in the region. We reviewed and evaluated the policies and interventions implemented by the Salvadoran National Malaria Program that likely contributed to this progress toward malaria elimination. Decentralization of the malaria program, early regional stratification by risk, and data-driven stratum-specific actions resulted in the timely and targeted allocation of resources for vector control, surveillance, case detection, and treatment. Weekly reporting by health workers and volunteer collaborators—distributed throughout the country by strata and informed via the national surveillance system—enabled local malaria teams to provide rapid, adaptive, and focalized program actions. Sustained investments in surveillance and response have led to a dramatic reduction in local transmission, with most current malaria cases in El Salvador due to importation from neighboring countries. Additional support for systematic elimination efforts in neighboring countries would benefit the region and may be needed for El Salvador to achieve and maintain malaria elimination. El Salvador’s experience provides a relevant case study that can guide the application of similar strategies in other countries committed to malaria elimination.
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Affiliation(s)
| | | | | | - Caterina Guinovart
- PATH Malaria Control and Elimination Partnership in Africa (MACEPA)/ISGlobal Collaboration, Barcelona Institute for Global Health (ISGlobal), Barcelona, Spain
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Markwalter CF, Jang IK, Burton RA, Domingo GJ, Wright DW. Biolayer interferometry predicts ELISA performance of monoclonal antibody pairs for Plasmodium falciparum histidine-rich protein 2. Anal Biochem 2017; 534:10-13. [PMID: 28698001 PMCID: PMC5552614 DOI: 10.1016/j.ab.2017.07.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 07/06/2017] [Accepted: 07/07/2017] [Indexed: 11/09/2022]
Abstract
Predicting antibody pair performance in a sandwich format streamlines development of antibody-based diagnostics and laboratory research tools, such as enzyme-linked immunosorbent assays (ELISAs) and lateral flow immunoassays (LFAs). We have evaluated panels of monoclonal antibodies against the malarial parasite biomarker Plasmodium falciparum histidine rich protein 2 (HRP2), including 9 new monoclonal antibodies, using biolayer interferometry (BLI) and screened antibody pairs in a checkerboard ELISA. This study showed BLI predicts antibody pair ELISA performance for HRP2. Pairs that included capture antibodies with low off-rate constants and detection antibodies with high on-rate constants performed best in an ELISA format. Kinetic parameters of 15 anti-HRP2 antibodies are measured by biolayer interferometry. Kinetic constants are compared to a checkerboard ELISA of 225 antibody pairs. Biolayer interferometry predicts antibody pair performance for HRP2 ELISA. Capture mAbs with low koff and detection mAbs with high kon are best in HRP2 ELISA.
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Affiliation(s)
- C F Markwalter
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | | | | | | | - D W Wright
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA.
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Burton RA. If brains could talk. Neurology 2017; 88:1872-1873. [DOI: 10.1212/wnl.0000000000003908] [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: 11/15/2022] Open
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Poole CB, Li Z, Alhassan A, Guelig D, Diesburg S, Tanner NA, Zhang Y, Evans TC, LaBarre P, Wanji S, Burton RA, Carlow CKS. Colorimetric tests for diagnosis of filarial infection and vector surveillance using non-instrumented nucleic acid loop-mediated isothermal amplification (NINA-LAMP). PLoS One 2017; 12:e0169011. [PMID: 28199317 PMCID: PMC5310896 DOI: 10.1371/journal.pone.0169011] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [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: 05/20/2016] [Accepted: 11/19/2016] [Indexed: 11/26/2022] Open
Abstract
Accurate detection of filarial parasites in humans is essential for the implementation and evaluation of mass drug administration programs to control onchocerciasis and lymphatic filariasis. Determining the infection levels in vector populations is also important for assessing transmission, deciding when drug treatments may be terminated and for monitoring recrudescence. Immunological methods to detect infection in humans are available, however, cross-reactivity issues have been reported. Nucleic acid-based molecular assays offer high levels of specificity and sensitivity, and can be used to detect infection in both humans and vectors. In this study we developed loop-mediated isothermal amplification (LAMP) tests to detect three different filarial DNAs in human and insect samples using pH sensitive dyes for enhanced visual detection of amplification. Furthermore, reactions were performed in a portable, non-instrumented nucleic acid amplification (NINA) device that provides a stable heat source for LAMP. The efficacy of several strand displacing DNA polymerases were evaluated in combination with neutral red or phenol red dyes. Colorimetric NINA-LAMP assays targeting Brugia Hha I repeat, Onchocerca volvulus GST1a and Wuchereria bancrofti LDR each exhibit species-specificity and are also highly sensitive, detecting DNA equivalent to 1/10-1/5000th of one microfilaria. Reaction times varied depending on whether a single copy gene (70 minutes, O. volvulus) or repetitive DNA (40 min, B. malayi and W. bancrofti) was employed as a biomarker. The NINA heater can be used to detect multiple infections simultaneously. The accuracy, simplicity and versatility of the technology suggests that colorimetric NINA-LAMP assays are ideally suited for monitoring the success of filariasis control programs.
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Affiliation(s)
| | - Zhiru Li
- New England Biolabs, Ipswich, MA United States of America
| | - Andy Alhassan
- New England Biolabs, Ipswich, MA United States of America
| | - Dylan Guelig
- PATH, Seattle, Washington, United States of America
| | | | | | - Yinhua Zhang
- New England Biolabs, Ipswich, MA United States of America
| | | | - Paul LaBarre
- PATH, Seattle, Washington, United States of America
| | - Samuel Wanji
- Research Foundation in Tropical Diseases and Environment, Buea, Cameroon
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Curtis KA, Rudolph DL, Morrison D, Guelig D, Diesburg S, McAdams D, Burton RA, LaBarre P, Owen M. Single-use, electricity-free amplification device for detection of HIV-1. J Virol Methods 2016; 237:132-137. [PMID: 27616198 DOI: 10.1016/j.jviromet.2016.09.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 09/07/2016] [Indexed: 11/19/2022]
Abstract
Early and accurate diagnosis of HIV is key for the reduction of transmission and initiation of patient care. The availability of a rapid nucleic acid test (NAT) for use at the point-of-care (POC) will fill a gap in HIV diagnostics, improving the diagnosis of acute infection and HIV in infants born to infected mothers. In this study, we evaluated the performance of non-instrumented nucleic acid amplification, single-use disposable (NINA-SUD) devices for the detection of HIV-1 in whole blood using reverse-transcription, loop-mediated isothermal amplification (RT-LAMP) with lyophilized reagents. The NINA-SUD heating device harnesses the heat from an exothermic chemical reaction initiated by the addition of saline to magnesium iron powder. Reproducibility was demonstrated between NINA-SUD units and comparable, if not superior, performance for detecting clinical specimens was observed as compared to the thermal cycler. The stability of the lyophilized HIV-1 RT-LAMP reagents was also demonstrated following storage at -20, 4, 25, and 30°C for up to one month. The single-use, disposable NAT minimizes hands-on time and has the potential to facilitate HIV-1 testing in resource-limited settings or at the POC.
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Affiliation(s)
- Kelly A Curtis
- Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30329, USA.
| | - Donna L Rudolph
- Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30329, USA
| | - Daphne Morrison
- Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30329, USA
| | - Dylan Guelig
- PATH, 2201 Westlake Avenue, Suite 200, Seattle, WA 98121, USA
| | - Steven Diesburg
- PATH, 2201 Westlake Avenue, Suite 200, Seattle, WA 98121, USA
| | - David McAdams
- PATH, 2201 Westlake Avenue, Suite 200, Seattle, WA 98121, USA
| | - Robert A Burton
- PATH, 2201 Westlake Avenue, Suite 200, Seattle, WA 98121, USA
| | - Paul LaBarre
- PATH, 2201 Westlake Avenue, Suite 200, Seattle, WA 98121, USA
| | - Michele Owen
- Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30329, USA
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8
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Mohon AN, Lee LDY, Bayih AG, Folefoc A, Guelig D, Burton RA, LaBarre P, Chan W, Meatherall B, Pillai DR. NINA-LAMP compared to microscopy, RDT, and nested PCR for the detection of imported malaria. Diagn Microbiol Infect Dis 2016; 85:149-53. [PMID: 27017271 PMCID: PMC4862928 DOI: 10.1016/j.diagmicrobio.2015.11.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 10/06/2015] [Accepted: 11/08/2015] [Indexed: 01/08/2023]
Abstract
Microscopy and field adaptable rapid diagnostic tests (RDTs) are not sensitive and specific in certain conditions such as poor training of microscopists, lack of electricity, or lower sensitivity in the detection of non-falciparum malaria. More sensitive point-of-care testing (POCT) would reduce delays in diagnosis and initiation of therapy. In the current study, we have evaluated the efficacy of noninstrumented nucleic acid amplification (NINA) coupled with loop-mediated isothermal amplification (LAMP) for detection of traveler's malaria (n=140) in comparison with microscopy, nested PCR, and the only Food and Drug Administration-approved rapid diagnostic test. NINA-LAMP was 100% sensitive and 98.6% specific when compared to nested PCR. For non-falciparum detection, NINA-LAMP sensitivity was 100% sensitive compared to nested PCR, whereas RDT sensitivity was 71%. LAMP is highly sensitive and specific for symptomatic malaria diagnosis regardless of species.
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Affiliation(s)
- Abu Naser Mohon
- Department of Microbiology, Immunology and Infectious Disease, University of Calgary, AB, Canada; Department of Pathology and Laboratory Medicine, University of Calgary, AB, Canada
| | - Lydia Da-Yeong Lee
- Department of Microbiology, Immunology and Infectious Disease, University of Calgary, AB, Canada
| | - Abebe Genetu Bayih
- Department of Pathology and Laboratory Medicine, University of Calgary, AB, Canada
| | - Asongna Folefoc
- Department of Pathology and Laboratory Medicine, University of Calgary, AB, Canada
| | | | | | | | - Wilson Chan
- Department of Pathology and Laboratory Medicine, University of Calgary, AB, Canada
| | | | - Dylan R Pillai
- Department of Microbiology, Immunology and Infectious Disease, University of Calgary, AB, Canada; Department of Pathology and Laboratory Medicine, University of Calgary, AB, Canada; Department of Medicine, University of Calgary, Calgary, AB, Canada.
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9
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Tsurupa G, Hantgan RR, Burton RA, Pechik I, Tjandra N, Medved L. Structure, stability, and interaction of the fibrin(ogen) alphaC-domains. Biochemistry 2010; 48:12191-201. [PMID: 19928926 DOI: 10.1021/bi901640e] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Our recent study established the NMR structure of the recombinant bAalpha406-483 fragment corresponding to the NH(2)-terminal half of the bovine fibrinogen alphaC-domain and revealed that at increasing concentrations this fragment forms oligomers (self-associates). The major goals of the study presented here were to determine the structure and self-association of the full-length human fibrinogen alphaC-domains. To accomplish these goals, we prepared a recombinant human fragment, hAalpha425-503, homologous to bovine bAalpha406-483, and demonstrated using NMR, CD, and size-exclusion chromatography that its overall fold and ability to form oligomers are similar to those of bAalpha406-483. We also prepared recombinant hAalpha392-610 and bAalpha374-568 fragments corresponding to the full-length human and bovine alphaC-domains, respectively, and tested their structure, stability, and ability to self-associate. Size-exclusion chromatography revealed that both fragments form reversible oligomers in a concentration-dependent manner. Their oligomerization was confirmed in sedimentation equilibrium experiments, which also established the self-association affinities of these fragments and revealed that the addition of each monomer to assembling alphaC-oligomers substantially increases the stabilizing free energy. In agreement, unfolding experiments monitored by CD established that self-association of both fragments results in a significant increase in their thermal stability. Analysis of CD spectra of both fragments revealed that alphaC self-association results in an increase in the level of regular structure, implying that the COOH-terminal half of the alphaC-domain adopts an ordered conformation in alphaC-oligomers and that this domain contains two independently folded subdomains. Altogether, these data further clarify the structure of the human and bovine alphaC-domains and the molecular mechanism of their self-association into alphaC-polymers in fibrin.
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Affiliation(s)
- Galina Tsurupa
- Center for Vascular and Inflammatory Diseases and Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 800 West Baltimore Street, Baltimore, Maryland 21201, USA
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Zhang Y, Oh H, Burton RA, Burgner JW, Geahlen RL, Post CB. Tyr130 phosphorylation triggers Syk release from antigen receptor by long-distance conformational uncoupling. Proc Natl Acad Sci U S A 2008; 105:11760-5. [PMID: 18689684 PMCID: PMC2575281 DOI: 10.1073/pnas.0708583105] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Indexed: 12/26/2022] Open
Abstract
The Syk protein-tyrosine kinase plays a major role in signaling through the B cell receptor for antigen (BCR). Syk binds the receptor via its tandem pair of SH2 domains interacting with a doubly phosphorylated immunoreceptor tyrosine-based activation motif (dp-ITAM) of the BCR complex. Upon phosphorylation of Tyr-130, which lies between the two SH2 domains distant to the phosphotyrosine binding sites, Syk dissociates from the receptor. To understand the structural basis for this dissociation, we investigated the structural and dynamic characteristics of the wild type tandem SH2 region (tSH2) and a variant tandem SH2 region (tSH2(pm)) with Tyr-130 substituted by Glu to permanently introduce a negative charge at this position. NMR heteronuclear relaxation experiments, residual dipolar coupling measurements and analytical ultracentrifugation revealed substantial differences in the hydrodynamic behavior of tSH2 and tSH2(pm). Although the two SH2 domains in tSH2 are tightly associated, the two domains in tSH2(pm) are partly uncoupled and tumble in solution with a faster correlation time. In addition, the equilibrium dissociation constant for the binding of tSH2(pm) to dp-ITAM (1.8 microM) is significantly higher than that for the interaction between dp-ITAM and tSH2 but is close to that for a singly tyrosine-phosphorylated peptide binding to a single SH2 domain. Experimental data and hydrodynamic calculations both suggest a loss of domain-domain contacts and change in relative orientation upon the introduction of a negative charge on residue 130. A long-distance structural mechanism by which the phosphorylation of Y130 negatively regulates the interaction of Syk with immune receptors is proposed.
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Affiliation(s)
- Yajie Zhang
- *Department of Medicinal Chemistry and Molecular Pharmacology
| | - Hyunju Oh
- *Department of Medicinal Chemistry and Molecular Pharmacology
| | | | - John W. Burgner
- Markey Center for Structural Biology
- Bindley Bioscience Center and
| | - Robert L. Geahlen
- *Department of Medicinal Chemistry and Molecular Pharmacology
- Purdue Cancer Center, Purdue University, West Lafayette, IN 47907
| | - Carol Beth Post
- *Department of Medicinal Chemistry and Molecular Pharmacology
- Markey Center for Structural Biology
- Purdue Cancer Center, Purdue University, West Lafayette, IN 47907
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Burton RA, Tsurupa G, Hantgan RR, Tjandra N, Medved L. NMR solution structure, stability, and interaction of the recombinant bovine fibrinogen alphaC-domain fragment. Biochemistry 2007; 46:8550-60. [PMID: 17590019 PMCID: PMC2597398 DOI: 10.1021/bi700606v] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
According to the existing hypothesis, in fibrinogen, the COOH-terminal portions of two Aalpha chains are folded into compact alphaC-domains that interact intramolecularly with each other and with the central region of the molecule; in fibrin, the alphaC-domains switch to an intermolecular interaction resulting in alphaC-polymers. In agreement, our recent NMR study identified within the bovine fibrinogen Aalpha374-538 alphaC-domain fragment an ordered compact structure including a beta-hairpin restricted at the base by a 423-453 disulfide linkage. To establish the complete structure of the alphaC-domain and to further test the hypothesis, we expressed a shorter alphaC-fragment, Aalpha406-483, and performed detailed analysis of its structure, stability, and interactions. NMR experiments on the Aalpha406-483 fragment identified a second loose beta-hairpin formed by residues 459-476, yielding a structure consisting of an intrinsically unstable mixed parallel/antiparallel beta-sheet. Size-exclusion chromatography and sedimentation velocity experiments revealed that the Aalpha406-483 fragment forms soluble oligomers whose fraction increases with an increase in concentration. This was confirmed by sedimentation equilibrium analysis, which also revealed that the addition of each monomer to an assembling alphaC-oligomer substantially increases its stabilizing free energy. In agreement, unfolding experiments monitored by CD established that oligomerization of Aalpha406-483 results in increased thermal stability. Altogether, these experiments establish the complete NMR solution structure of the Aalpha406-483 alphaC-domain fragment, provide direct evidence for the intra- and intermolecular interactions between the alphaC-domains, and confirm that these interactions are thermodynamically driven.
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Affiliation(s)
- Robert A. Burton
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 Center Drive, Bethesda, MD 20892
| | - Galina Tsurupa
- Center for Vascular and Inflammatory Diseases and the Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 800 West Baltimore Street, Baltimore, MD 21201
| | - Roy R. Hantgan
- Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, NC 27157
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 Center Drive, Bethesda, MD 20892
- To whom correspondence should be addressed. Leonid Medved. E-mail: . Phone: (410) 706-8065. Fax (410) 706-8121. Nico Tjandra. E-mail: . Phone: (301) 402-3029. Fax (301) 402-3404
| | - Leonid Medved
- Center for Vascular and Inflammatory Diseases and the Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 800 West Baltimore Street, Baltimore, MD 21201
- To whom correspondence should be addressed. Leonid Medved. E-mail: . Phone: (410) 706-8065. Fax (410) 706-8121. Nico Tjandra. E-mail: . Phone: (301) 402-3029. Fax (301) 402-3404
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Burton RA, Tsurupa G, Medved L, Tjandra N. Identification of an Ordered Compact Structure within the Recombinant Bovine Fibrinogen αC-Domain Fragment by NMR. Biochemistry 2007. [DOI: 10.1021/bi700765r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Burton RA, Tjandra N. Residue-Specific 13C‘ CSA Tensor Principal Components for Ubiquitin: Correlation between Tensor Components and Hydrogen Bonding. J Am Chem Soc 2007; 129:1321-6. [PMID: 17263416 DOI: 10.1021/ja066835c] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The residue-specific 13C' CSA tensor principal components, sigma(11), sigma(22), sigma(33), and the tensor orientation defined by the rotation angles beta and gamma have been determined by solution NMR for uniformly labeled ubiquitin partially aligned in four different media. Spurious chemical shift deviations due to solvent effects were corrected with an offset calculated by linear regression of the residual dipolar couplings and chemical shifts at increasing alignment strengths. Analysis of this effect revealed no obvious correlation to solvent exposure. Data obtained in solution from a protein offer a better sampling of 13C' CSA for different amino acid types in a complex heterogeneous environment, thereby allowing for the evaluation of structural variables that would be challenging to achieve by other methods. The 13C' CSA principal components cluster about the average values previously determined, and experimental correlations observed between sigma(11), sigma(22) tensorial components and C'O...H(N) hydrogen bonding are discussed. The inverse association of sigma(11) and sigma(22) exemplify the calculated and solid-state NMR observed effect on the tensor components by hydrogen bonding. We also show that 13C' CSA tensors are sensitive to hydrogen-bond length but not hydrogen-bond angle. This differentiation was previously unavailable. Similarly, hydrogen bonding to the conjugated NH of the same peptide plane has no detectable effect. Importantly, the observed weak correlations signify the presence of confounding influences such as nearest-neighbor effects, side-chain conformation, electrostatics, and other long-range factors to the 13C' CSA tensor. These analyses hold future potential for exploration provided that more accurate data from a larger number of proteins and alignments become available.
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Affiliation(s)
- Robert A Burton
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 South Drive, Bethesda, Maryland 20892, USA
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Abstract
B-Myc is an endogenous, N-terminal homologue of transcription factor c-Myc that lacks the C-terminal DNA binding and protein dimerization domain of c-Myc. Clinical mutations in the c-Myc N-terminal region, and the subsequent misregulation of Myc, are implicated in the development of numerous human cancers. Myc functions to both activate and repress transcription by associating with multiple binding partners. We investigated the structural and dynamical properties of B-Myc, free or associated with the transactivation inhibitor, MM-1, and the activator, TBP, using NMR spectroscopy. B-Myc has no persistent tertiary structure, yet regions corresponding to Myc homology boxes 1 and 2 (MBI and MBII, respectively) have molten globule-like characteristics. B-Myc binds to MM-1 in a specific manner without becoming highly structured. The local regions of B-Myc involved in binding differ for MM-1 and TBP, and regions not identified by mutagenesis are found to be involved in MM-1 binding. The results provide new insights into Myc N-terminal protein-protein interactions. We propose a model for Myc regulation through differential involvement of MBI and MBII in the binding of Myc interacting proteins.
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Affiliation(s)
- Robert A Burton
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907-2091, USA
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Burton RA, Tjandra N. Determination of the residue-specific 15N CSA tensor principal components using multiple alignment media. J Biomol NMR 2006; 35:249-59. [PMID: 16823597 DOI: 10.1007/s10858-006-9037-6] [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] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2006] [Revised: 05/16/2006] [Accepted: 06/02/2006] [Indexed: 05/10/2023]
Abstract
The individual components of the backbone (15)N CSA tensor, sigma(11), sigma(22), sigma(33), and the orientation of sigma(11) relative to the NH bond described by the angle beta have been determined for uniformly labeled (15)N, (13)C ubiquitin from partial alignment in phospholipid bicelles, Pf1 phage, and poly(ethylene glycol) by measuring the residue-specific residual dipolar couplings and chemical shift deviations. No strong correlation between any of the CSA tensor components is observed with any single structural feature. However, the experimentally determined tensor components agree with the previously determined average CSA principal components [Cornilescu and Bax (2000) J. Am. Chem. Soc. 122, 10143-10154]. Significant deviations from the averages coincide with residues in beta-strand or extended regions, while alpha-helical residue tensor components cluster close to the average values.
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Affiliation(s)
- Robert A Burton
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 South Drive, Bethesda, Maryland, 20892, USA
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Burton RA, Tsurupa G, Medved L, Tjandra N. Identification of an ordered compact structure within the recombinant bovine fibrinogen alphaC-domain fragment by NMR. Biochemistry 2006; 45:2257-66. [PMID: 16475814 PMCID: PMC2597476 DOI: 10.1021/bi052380c] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The NMR solution structure of the bovine fibrinogen alphaC-domain fragment, including residues Aalpha374-538, reveals a type-I' beta-hairpin, restricted at the base by a C423-C453 disulfide linkage and a short turn preceding C423. Although both faces of the hairpin are formed mainly by hydrophilic residues, one of them is uncharged while the other has a characteristic pattern of charged residues which are highly conserved among vertebrate species. Chemical shift indexing and relaxation data indicate the presence of a collapsed hydrophobic region next to the hairpin that includes approximately 30 residues with slower concerted motion and higher content of nonpolar residues and, according to a previous study (Tsurupa, G., Tsonev, L., and Medved, L. (2002) Biochemistry 41, 6449-6459), may cooperate with the hairpin to form a compact cooperative unit (domain). Structure and relaxation data show that the region between C423 and C453 is populated by both random coil and beta-structure, suggesting that the cooperative structure in the isolated alphaC-domain is intrinsically unstable. This observation is in agreement with a very low energy of stabilization of the Aalpha374-538 fragment determined in unfolding experiments. The low stability of the alphaC-domain suggests a possible explanation for the previously observed intra- and intermolecular interactions of these domains in fibrinogen and fibrin.
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Affiliation(s)
- Robert A. Burton
- Laboratory of Biophysical Chemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 Center Drive, Bethesda, MD 20892
| | - Galina Tsurupa
- Center for Vascular and Inflammatory Diseases and the Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 800 West Baltimore Street, Baltimore, MD 21201
| | - Leonid Medved
- Center for Vascular and Inflammatory Diseases and the Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 800 West Baltimore Street, Baltimore, MD 21201
- To whom correspondence should be addressed: Nico Tjandra ; phone (301) 402-3029; fax (301) 402-3404, Leonid Medved ; (410) 706-8065; fax (410) 706-8121
| | - Nico Tjandra
- Laboratory of Biophysical Chemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 Center Drive, Bethesda, MD 20892
- To whom correspondence should be addressed: Nico Tjandra ; phone (301) 402-3029; fax (301) 402-3404, Leonid Medved ; (410) 706-8065; fax (410) 706-8121
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Lee RC, Burton RA, Hrmova M, Fincher GB. Barley arabinoxylan arabinofuranohydrolases: purification, characterization and determination of primary structures from cDNA clones. Biochem J 2001; 356:181-9. [PMID: 11336650 PMCID: PMC1221826 DOI: 10.1042/0264-6021:3560181] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A family 51 arabinoxylan arabinofuranohydrolase, designated AXAH-I, has been purified from extracts of 7-day-old barley (Hordeum vulgare L.) seedlings by fractional precipitation with (NH(4))(2)SO(4) and ion-exchange chromatography. The enzyme has an apparent molecular mass of 65 kDa and releases L-arabinose from cereal cell wall arabinoxylans with a pH optimum of 4.3, a catalytic rate constant (k(cat)) of 6.9 s(-1) and a catalytic efficiency factor (k(cat)/K(m)) of 0.76 (ml x s(-1) x mg(-1)). Whereas the hydrolysis of alpha-L-arabinofuranosyl residues linked to C(O)3 of backbone (1-->4)-beta-xylosyl residues proceeds at the fastest rate, alpha-L-arabinofuranosyl residues on doubly substituted xylosyl residues are also hydrolysed, at lower rates. A near full-length cDNA encoding barley AXAH-I indicates that the mature enzyme consists of 626 amino acid residues and has a calculated pI of 4.8. A second cDNA, which is 81% identical with that encoding AXAH-I, encodes another barley AXAH, which has been designated AXAH-II. The barley AXAHs are likely to have key roles in wall metabolism in cereals and other members of the Poaceae. Thus the enzymes could participate in the modification of the fine structure of arabinoxylan during wall deposition, maturation or expansion, or in wall turnover and the hydrolysis of arabinoxylans in germinated grain.
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Affiliation(s)
- R C Lee
- Department of Plant Science, Adelaide University, Waite Campus, Glen Osmond, SA 5064, Australia
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Burton RA. Medicine and the arts. Doc in a Box. Acad Med 2000; 75:724-725. [PMID: 10926024 DOI: 10.1097/00001888-200007000-00017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Gaul BS, Harrison ML, Geahlen RL, Burton RA, Post CB. Substrate recognition by the Lyn protein-tyrosine kinase. NMR structure of the immunoreceptor tyrosine-based activation motif signaling region of the B cell antigen receptor. J Biol Chem 2000; 275:16174-82. [PMID: 10748115 DOI: 10.1074/jbc.m909044199] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The immunoreceptor tyrosine-based activation motif (ITAM) plays a central role in transmembrane signal transduction in hematopoietic cells by mediating responses leading to proliferation and differentiation. An initial signaling event following activation of the B cell antigen receptor is phosphorylation of the CD79a (Ig-alpha) ITAM by Lyn, a Src family protein-tyrosine kinase. To elucidate the structural basis for recognition between the ITAM substrate and activated Lyn kinase, the structure of an ITAM-derived peptide bound to Lyn was determined using exchange-transferred nuclear Overhauser NMR spectroscopy. The bound substrate structure has an irregular helix-like character. Docking based on the NMR data into the active site of the closely related Lck kinase strongly favors ITAM binding in an orientation similar to binding of cyclic AMP-dependent protein kinase rather than that of insulin receptor tyrosine kinase. The model of the complex provides a rationale for conserved ITAM residues, substrate specificity, and suggests that substrate binds only the active conformation of the Src family tyrosine kinase, unlike the ATP cofactor, which can bind the inactive form.
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Affiliation(s)
- B S Gaul
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907-1333, USA
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Burton RA, Gibeaut DM, Bacic A, Findlay K, Roberts K, Hamilton A, Baulcombe DC, Fincher GB. Virus-induced silencing of a plant cellulose synthase gene. Plant Cell 2000. [PMID: 10810144 DOI: 10.2307/3870995] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infected with one group of cDNAs had much shorter internode lengths, small leaves, and a "dwarf" phenotype. Consistent with a loss of cell wall cellulose, abnormally large and in many cases spherical cells ballooned from the undersurfaces of leaves, particularly in regions adjacent to vascular tissues. Linkage analyses of wall polysaccharides prepared from infected leaves revealed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected plants. The decrease in cellulose content in cell walls was offset by an increase in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from approximately 50 to approximately 33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellulose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellulose synthase genes.
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Affiliation(s)
- R A Burton
- Department of Plant Science, University of Adelaide, South Australia, Australia
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Burton RA, Gibeaut DM, Bacic A, Findlay K, Roberts K, Hamilton A, Baulcombe DC, Fincher GB. Virus-induced silencing of a plant cellulose synthase gene. Plant Cell 2000; 12:691-706. [PMID: 10810144 PMCID: PMC139921 DOI: 10.1105/tpc.12.5.691] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infected with one group of cDNAs had much shorter internode lengths, small leaves, and a "dwarf" phenotype. Consistent with a loss of cell wall cellulose, abnormally large and in many cases spherical cells ballooned from the undersurfaces of leaves, particularly in regions adjacent to vascular tissues. Linkage analyses of wall polysaccharides prepared from infected leaves revealed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected plants. The decrease in cellulose content in cell walls was offset by an increase in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from approximately 50 to approximately 33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellulose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellulose synthase genes.
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Affiliation(s)
- R A Burton
- Department of Plant Science, University of Adelaide, South Australia, Australia
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Burton RA, Zhang XQ, Hrmova M, Fincher GB. A single limit dextrinase gene is expressed both in the developing endosperm and in germinated grains of barley. Plant Physiol 1999; 119:859-71. [PMID: 10069825 PMCID: PMC32101 DOI: 10.1104/pp.119.3.859] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/1998] [Accepted: 12/02/1998] [Indexed: 05/17/2023]
Abstract
The single gene encoding limit dextrinase (pullulan 6-glucanohydrolase; EC 3.2.1.41) in barley (Hordeum vulgare) has 26 introns that range in size from 93 to 822 base pairs. The mature polypeptide encoded by the gene has 884 amino acid residues and a calculated molecular mass of 97,417 D. Limit dextrinase mRNA is abundant in gibberellic acid-treated aleurone layers and in germinated grain. Gibberellic acid response elements were found in the promoter region of the gene. These observations suggest that the enzyme participates in starch hydrolysis during endosperm mobilization in germinated grain. The mRNA encoding the enzyme is present at lower levels in the developing endosperm of immature grain, a location consistent with a role for limit dextrinase in starch synthesis. Enzyme activity was also detected in developing grain. The limit dextrinase has a presequence typical of transit peptides that target nascent polypeptides to amyloplasts, but this would not be expected to direct secretion of the mature enzyme from aleurone cells in germinated grain. It remains to be discovered how the enzyme is released from the aleurone and whether another enzyme, possibly of the isoamylase group, might be equally important for starch hydrolysis in germinated grain.
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Affiliation(s)
- R A Burton
- Department of Plant Science, University of Adelaide, Waite Campus, Glen Osmond, South Australia 5064, Australia
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Bewley JD, Burton RA, Morohashi Y, Fincher GB. Molecular cloning of a cDNA encoding a (1-->4)-beta-mannan endohydrolase from the seeds of germinated tomato (Lycopersicon esculentum). Planta 1997; 203:454-459. [PMID: 9421930 DOI: 10.1007/s004250050214] [Citation(s) in RCA: 23] [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] [Indexed: 05/22/2023]
Abstract
Mannose-containing polysaccharides are widely distributed in cell walls of higher plants. During endosperm mobilization in germinated tomato seeds (1-->4)-beta-mannan endohydrolases (EC 3.2.1.78) participate in the enzymic depolymerization of these cell wall polysaccharides. A cDNA encoding a (1-->4)-beta-mannanase from the endosperm of germinated tomato (Lycopersicon esculentum Mill.) seeds has been isolated and characterized. The amino acid sequence deduced from the 5'-region of the cDNA exactly matches the sequence of the 65 NH2-terminal amino acids determined directly from the purified enzyme. The mature enzyme consists of 346 amino acid residues, it has a calculated M(r) of 38,950 and an isoelectric point of 5.3. Overall, the enzyme exhibits only 28-30% sequence identity with fungal (1-->4)-beta-mannanases, but more highly conserved regions, which may represent catalytic and substrate-binding domains, can be identified. Based on classification of the tomato (1-->4)-beta-mannanase as a member of the family 5 group of glycosyl hydrolases, Glu-148 and Glu-265 would be expected to be the catalytic acid and the catalytic nucleophile, respectively. Southern hybridization analyses indicate that the enzyme is derived from a family of about four genes. Expression of the genes, as determined by the presence of mRNA transcripts in Northern hybridization analyses, occurs in the endosperm of germinated seeds; no transcripts are detected in hypocotyls, cotyledons, roots or leaves.
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Affiliation(s)
- J D Bewley
- Department of Botany, University of Guelph, Ontario, Canada.
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Burton RA. Neurology and murderers. Neurology 1996; 47:1610; author reply 1610-1. [PMID: 8960768 DOI: 10.1212/wnl.47.6.1610-d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
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Burton RA, Bewley JD, Smith AM, Bhattacharyya MK, Tatge H, Ring S, Bull V, Hamilton WD, Martin C. Starch branching enzymes belonging to distinct enzyme families are differentially expressed during pea embryo development. Plant J 1995; 7:3-15. [PMID: 7894509 DOI: 10.1046/j.1365-313x.1995.07010003.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
cDNA clones for two isoforms of starch branching enzyme (SBEI and SBEII) have been isolated from pea embryos and sequenced. The deduced amino acid sequences of pea SBEI and SBEII are closely related to starch branching enzymes of maize, rice, potato and cassava and a number of glycogen branching enzymes from yeast, mammals and several prokaryotic species. In comparison with SBEI, the deduced amino acid sequence of SBEII lacks a flexible domain at the N-terminus of the mature protein. This domain is also present in maize SBEII and rice SBEIII and resembles one previously reported for pea granule-bound starch synthase II (GBSSII). However, in each case it is missing from the other isoform of SBE from the same species. On the basis of this structural feature (which exists in some isoforms from both monocots and dicots) and other differences in sequence, SBEs from plants may be divided into two distinct enzyme families. There is strong evidence from our own and other work that the amylopectin products of the enzymes from these two families are qualitatively different. Pea SBEI and SBEII are differentially expressed during embryo development. SBEI is relatively highly expressed in young embryos whilst maximum expression of SBEII occurs in older embryos. The differential expression of isoforms which have distinct catalytic properties means that the contribution of each SBE isoform to starch biosynthesis changes during embryo development. Qualitative measurement of amylopectin from developing and maturing embryos confirms that the nature of amylopectin changes during pea embryo development and that this correlates with the differential expression of SBE isoforms.
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Affiliation(s)
- R A Burton
- Department of Genetics and Applied Genetics, John Innes Institute, John Innes Centre, Norwich, UK
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Burton RA, Raskin NH. Remediable seizure disorder due to alimentary hypoglycemia. Neurology 1970; 20:380. [PMID: 5534990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
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Burton RA. Nursing shortage: reality or illusion? Hosp Top 1967; 45:38-43. [PMID: 6016441 DOI: 10.1080/00185868.1967.9952002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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Burton RA. Some West Indian Snakes of the Genus Alsophis. COPEIA 1939. [DOI: 10.2307/1436889] [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]
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