Structure of a multifunctional protein. Mammalian phosphatidylinositol transfer protein complexed with phosphatidylcholine

Eukaryotic phosphatidylinositol transfer protein is a ubiquitous multifunctional protein that transports phospholipids between membrane surfaces and participates in cellular phospholipid metabolism during signal transduction and vesicular trafficking. The three-dimensional structure of the alpha-isoform of rat phosphatidylinositol transfer protein complexed with one molecule of phosphatidylcholine, one of its physiological ligands, has been determined to 2.2 A resolution by x-ray diffraction techniques. A single beta-sheet and several long alpha-helices define an enclosed internal cavity in which a single molecule of the phospholipid is accommodated with its polar head group in the center of the protein and fatty acyl chains projected toward the surface. Other structural features suggest mechanisms by which cytosolic phosphatidylinositol transfer protein interacts with membranes for lipid exchange and associates with a variety of lipid and protein kinases.

mDYRK3 kinase is expressed selectively in late erythroid progenitor cells and attenuates colony-forming unit-erythroid development

DYRKs are a new subfamily of dual-specificity kinases that was originally discovered on the basis of homology to Yak1, an inhibitor of cell cycle progression in yeast. At present, mDYRK-3 and mDYRK-2 have been cloned, and mDYRK-3 has been characterized with respect to kinase activity, expression among tissues and hematopoietic cells, and possible function during erythropoiesis. In sequence, mDYRK-3 diverges markedly in noncatalytic domains from mDYRK-2 and mDYRK-1a, but is 91.3% identical overall to hDYRK-3. Catalytically, mDYRK-3 readily phosphorylated myelin basic protein (but not histone 2B) and also appeared to autophosphorylate in vitro. Expression of mDYRK-1a, mDYRK-2, and mDYRK-3 was high in testes, but unlike mDYRK1a and mDYRK 2, mDYRK-3 was not expressed at appreciable levels in other tissues examined. Among hematopoietic cells, however, mDYRK-3 expression was selectively elevated in erythroid cell lines and primary pro-erythroid cells. In developmentally synchronized erythroid progenitor cells, expression peaked sharply following exposure to erythropoietin plus stem cell factor (SCF) (but not SCF alone), and in situ hybridizations of sectioned embryos revealed selective expression of mDYRK-3 in fetal liver. Interestingly, antisense oligonucleotides to mDYRK-3 were shown to significantly and specifically enhance colony-forming unit-erythroid colony formation. Thus, it is proposed that mDYRK-3 kinase functions as a lineage-restricted, stage-specific suppressor of red cell development. (Blood. 2001;97:901-910)

Purification, crystallization and x-ray analysis of crystals of pectate lyase A from Exwinia chrysanthemi

Pectate lyase A is secreted by Erwinia chrysanthemi and is a virulence factor for soft rot diseases in plants. Crystals of pectate lyase A were obtained by vapor-diffusion techniques in the presence of polyethylene glycol. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 48.96, b = 148.86, c = 78.61 A, beta = 97.32 degrees. The crystals contain two protein molecules of 38 kDa per asymmetric unit and diffract to 2.4 A using Cu Kalpha radiation.

X-ray analysis of crystals of rat phosphatidylinositol-transfer protein with bound phosphatidylcholine

Phosphatidylinositol-transfer protein (PITP) is a soluble, ubiquitously expressed, highly conserved protein encoded by two genes in humans, rodents and other mammals. A cDNA encoding the alpha isoform of the rat gene was expressed to high levels in Escherichia coli, the protein purified and the homogeneous protein used for crystallization studies. Crystals of rat PITP-alpha were obtained by vapor-diffusion techniques using the sitting-drop method. Crystals grow within two weeks by vapor-diffusion techniques in the presence of polyethylene glycol 4000. Both crystal forms pack in the monoclinic space group P21. Crystal form I has unit-cell parameters a = 44.75, b = 74.25, c = 48.32 A and beta = 114.14 degrees. Unit-cell parameters for crystal form II are a = 47.86, b = 73.59, c = 80.49 A and beta = 98.54 degrees. Crystal form I has a Vm of 2.295 A3 Da-1 and an estimated solvent content of 46.4% with one molecule per asymmetric unit, while crystal form II has a Vm of 2.196 A3 Da-1 and an estimated solvent content of 44.0%, assuming two molecules per asymmetric unit.

An alpha to beta conformational switch in EF-Tu

BACKGROUND

The bacterial elongation factor EF-Tu recognizes and transports aminoacyl-tRNAs to mRNA-programmed ribosomes. EF-Tu shares many structural and functional properties with other GTPases whose conformations are regulated by guanine nucleotides.

RESULTS

An intact form of Escherichia coli EF-Tu complexed with GDP has been crystallized in the presence of the EF-Tu-specific antibiotic GE2270 A. The three-dimensional structure has been solved by X-ray diffraction analysis and refined to a final crystallographic R factor of 17.2% at a resolution of 2.5 A. The location of the GE2270 A antibiotic-binding site could not be identified.

CONCLUSIONS

The structure of EF-Tu-GDP is nearly identical to that of a trypsin-modified form of EF-Tu-GDP, demonstrating conclusively that the protease treatment had not altered any essential structural features. The present structure represents the first view of an ordered Switch I region in EF-Tu-GDP and reveals similarities with two other GTPases complexed with GDP: Ran and ADP-ribosylation factor-1. A comparison of the Switch I regions of the GTP and GDP forms of EF-Tu also reveals that a segment, six amino acids in length, completely converts from an alpha helix in the GTP complex to beta secondary structure in the GDP form. The alpha to beta switch in EF-Tu may represent a prototypical activation mechanism for other protein families.

The Refined Three-Dimensional Structure of Pectate Lyase E from Erwinia chrysanthemi at 2.2 A Resolution

The crystal structure of pectate lyase E (PelE; EC 4.2.2.2) from the enterobacteria Erwinia chrysanthemi has been refined by molecular dynamics techniques to a resolution of 2.2 A and an R factor (an agreement factor between observed structure factor amplitudes) of 16.1%. The final model consists of all 355 amino acids and 157 water molecules. The root-mean-square deviation from ideality is 0.009 A for bond lengths and 1.721[deg] for bond angles. The structure of PelE bound to a lanthanum ion, which inhibits the enzymatic activity, has also been refined and compared to the metal-free protein. In addition, the structures of pectate lyase C (PelC) in the presence and absence of a lutetium ion have been refined further using an improved algorithm for identifying waters and other solvent molecules. The two putative active site regions of PelE have been compared to those in the refined structure of PelC. The analysis of the atomic details of PelE and PelC in the presence and absence of lanthanide ions provides insight into the enzymatic mechanism of pectate lyases.

X-ray analysis of crystals of polygalacturonase A fromPseudomonas solanacearum

Crystals of the pectolytic protein, polygalacturonase A, have been obtained from polyethylene glycol 8000 using vapor diffusion methods. The 52.4 kDa protein is secreted by the plant pathogenic bacteria Pseudomonas solanacearum, and is important in the virulence of this plant pathogen. The protein crystallizes in space group P2(1) and has unit-cell parameters of a = 101.9, b = 124.6, c = 48.1 A, and beta= 105 degrees 50'. The crystal has two molecules in the asymmetric unit, and diffracts maximally to a resolution of 2.1 A.

Structure-based multiple alignment of extracellular pectate lyase sequences

Pectate lyases are secreted virulence factors which degrade the pectate component of plant cell walls. The evolutionary-based multiple alignment of extracellular pectate lyases has been corrected using three-dimensional structural information derived from Erwinia chyrsanthemi pectate lyases C and E. The new multiple alignment reveals invariant amino acids likely to be involved in two different enzymatic functions.

Functional implications of structure-based sequence alignment of proteins in the extracellular pectate lyase superfamily

Pectate lyases are plant virulence factors that degrade the pectate component of the plant cell wall. The enzymes share considerable sequence homology with plant pollen and style proteins, suggesting a shared structural topology and possibly functional relationships as well. The three-dimensional structures of two Erwinia chrysanthemi pectate lyases, C and E, have been superimposed and the structurally conserved amino acids have been identified. There are 232 amino acids that superimpose with a root-mean-square deviation of 3 A or less. These amino acids have been used to correct the primary sequence alignment derived from evolution-based techniques. Subsequently, multiple alignment techniques have allowed the realignment of other extracellular pectate lyases as well as all sequence homologs, including pectin lyases and the plant pollen and style proteins. The new multiple sequence alignment reveals amino acids likely to participate in the parallel beta helix motif, those involved in binding Ca2+, and those invariant amino acids with potential catalytic properties. The latter amino acids cluster in two well-separated regions on the pectate lyase structures, suggesting two distinct enzymatic functions for extracellular pectate lyases and their sequence homologs.

Protein motifs. 3. The parallel beta helix and other coiled folds

A new type of structural domain, composed of all parallel beta strands, has been observed within the last year. An analysis of the basic types suggests that there are two distinct classes: the parallel beta helices, which belong to a tri beta-strand category, and the beta roll, which belongs to a di beta-strand category. The novel structural features of each class are described and the proteins belonging to each category are summarized. Proteins with the parallel beta helix fold include three pectate lyases and the tailspike protein from P22 phage. Proteins with the beta roll fold include two alkaline proteases. Although the parallel beta composition is emphasized, the same set of proteins share another common structural feature with several other proteins containing alpha helices: the polypeptide backbone is folded into a coiled structure in which each coil has the same 3-dimensional arrangement of a group of secondary structural elements. In addition to parallel beta domains, the other groups include the alpha/beta coiled fold, as represented by ribonuclease inhibitor, and the alpha/alpha coiled fold, as represented by lipovitellin and soluble lytic transglycoslyase. Novel features of the alpha/beta and alpha/alpha coiled folds are summarized.

The Refined Three-Dimensional Structure of Pectate Lyase C from Erwinia chrysanthemi at 2.2 Angstrom Resolution (Implications for an Enzymatic Mechanism)

The crystal structure of pectate lyase C (EC 4.2.2.2) from the enterobacterium Erwinia chrysanthemi (PelC) has been refined by molecular dynamics techniques to a resolution of 2.2 A to an R factor of 17.97%. The final model consists of 352 of the total 353 amino acids and 114 solvent molecules. The root-mean-square deviation from ideality is 0.009 A for bond lengths and 1.768[deg] for bond angles. The structure of PelC bound to the lanthanide ion lutetium, used as a calcium analog, has also been refined. Lutetium inhibits the enzymatic activity of the protein, and in the PelC-lutetium structure, the ion binds in the putative calcium-binding site. Five side-chain atoms form ligands to the lutetium ion. An analysis of the atomic-level model of the two protein structures reveals possible implications for the enzymatic mechanism of the enzyme.

Parallel beta-domains: a new fold in protein structures

A new type of structural domain, composed of parallel beta-strands folded into a coiled structure, has been observed in several protein structures within the past year. An analysis of the basic motif indicates that there are two distinct types, with variations likely to be discovered in the future.

The Three-Dimensional Structure of Pectate Lyase E, a Plant Virulence Factor from Erwinia chrysanthemi

The three-dimensional structure of pectate lyase E (PelE) has been determined by crystallographic techniques at a resolution of 2.2 A. The model includes all 355 amino acids but no solvent, and refines to a crystallographic refinement factor of 20.6%. The polypeptide backbone folds into a large right-handed cylinder, termed a parallel [beta] helix. Loops of various sizes and conformations protrude from the central helix and probably confer function. A putative Ca2+-binding site as well as two cationic sites have been deduced from the location of heavy atom derivatives. Comparison of the PelE and recently determined pectate lyase C (PelC) structures has led to identification of a putative polygalacturonate-binding region in PelE. Structural differences relevant to differences in the enzymatic mechanism and maceration properties of PelE and PelC have been identified. The comparative analysis also reveals a large degree of structural conservation of surface loops in one region as well as an apparent aromatic specificity pocket in the amino-terminal branch. Also discussed is the sequence and possible functional relationship of the pectate lyases with pollen and style plant proteins.

Unusual structural features in the parallel beta-helix in pectate lyases

BACKGROUND

A new type of domain structure, an all parallel beta class, has recently been observed in two pectate lyases, PelC and PelE. The atomic models have been analyzed to determine whether the new tertiary fold exhibits unusual structural features.

RESULTS

The polypeptide backbone exhibits no new types of secondary structural elements. However, novel features occur in the amino acid side chain interactions. The side chain atoms form linear stacks that include asparagine ladders, serine stacks, aliphatic stacks, and ringed-residue stacks. A new type of beta-sandwich between parallel beta-sheets is observed with properties that are more characteristic of antiparallel beta-sheets.

CONCLUSION

An analysis of the PelC and PelE structures, belonging to an all parallel beta structural class, reveals novel amino acid side chain interactions, a new type of beta-sandwich and an atypical amino acid composition of parallel beta-sheets. The findings are relevant to three-dimensional structural predictions.

New domain motif: the structure of pectate lyase C, a secreted plant virulence factor

Pectate lyases are secreted by pathogens and initiate soft-rot diseases in plants by cleaving polygalacturonate, a major component of the plant cell wall. The three-dimensional structure of pectate lyase C from Erwinia chrysanthemi has been solved and refined to a resolution of 2.2 angstroms. The enzyme folds into a unique motif of parallel beta strands coiled into a large helix. Within the core, the amino acids form linear stacks and include a novel asparagine ladder. The sequence similarities that pectate lyases share with pectin lyases, pollen and style proteins, and tubulins suggest that the parallel beta helix motif may occur in a broad spectrum of proteins.

Preliminary crystallographic analysis of the plant pathogenic factor, pectate lyase C from Erwinia chrysanthemi

Pectate lyases are saccharide-binding enzymes that degrade plant cell walls. One pectate lyase from Erwinia chrysanthemi (EC16), termed pectate lyase C, has been crystallized from ammonium sulfate. The preliminary x-ray diffraction analysis indicates that the crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit cell dimensions, a = 73.4 A, b = 80.3 A, and c = 95.1 A. The crystals diffract to a resolution of 2.2 A and have one molecule/asymmetric unit.