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1.  Crystallographic structure determination of B10 mutants of Vitreoscilla hemoglobin: role of Tyr29 (B10) in the structure of the ligand-binding site 
Acta Crystallographica Section F  2013;69(Pt 3):215-222.
The crystal structures of two mutants at position 29 of the dimeric hemoglobin from Vitreoscilla are reported, together with a discussion of the significance of these mutations.
Site-directed mutants of the gene encoding wild-type Vitreoscilla hemoglobin were made that changed Tyr29 (B10) of the wild-type Vitreoscilla hemoglobin (VHb) to either Phe or Ala. The wild-type and the two mutant hemoglobins were expressed in Escherichia coli and purified to homogeneity. The binding of the two mutants to CO was essentially identical to that of wild-type VHb as determined by CO-difference spectra. Circular-dichroism spectra also showed the two mutants to be essentially the same as wild-type VHb regarding overall helicity. All three VHbs were crystallized and their structures were determined at resolutions of 1.7–1.9 Å, which are similar to that of the original wild-type structure determination. The Tyr29Phe mutant has a structure that is essentially indistinguishable from that of the wild type. However, the structure of the Tyr29Ala mutant has significant differences from that of the wild type. In addition, for the Tyr29Ala mutant it was possible to determine the positions of most of the residues in the D region, which was disordered in the originally reported structure of wild-type VHb as well as in the wild-type VHb structure reported here. In the Tyr29Ala mutant, the five-membered ring of proline E8 (Pro54) occupies the space occupied by the aromatic ring of Tyr29 in the wild-type structure. These results are discussed in the context of the proposed role of Tyr29 in the structure of the oxygen-binding pocket.
PMCID: PMC3606562  PMID: 23519792
bacterial hemoglobin; Vitreoscilla; site-directed mutagenesis
2.  Purification and crystallization of Cor a 9, a major hazelnut allergen 
The major hazelnut allergen Cor a 9 was purified from the natural source and crystallized. Diffraction data were collected to 1.9 Å resolution using a synchrotron-radiation source.
Hazelnut (Corylus avellana) is one of the food sources that induce allergic reaction in a subpopulation of people with food allergy. The 11S legumin-like seed-storage protein from hazelnut has been identified as one of the major hazelnut allergens and named Cor a 9. In this study, Cor a 9 was extracted from hazelnut kernels using a high-salt solution and was purified by desalting out and FPLC to a highly purified state. Diffraction-quality single crystals were obtained using the hanging-drop vapour-diffusion method. Diffraction data were collected and a structure solution has been obtained by molecular-replacement calculations. Further refinement of the structure is currently in progress.
PMCID: PMC2628846  PMID: 19153454
hazelnuts; 11S seed-storage proteins; food allergies; tree-nut allergens
3.  Biochemical and Structural Characterization of the Secreted Chorismate Mutase (Rv1885c) from Mycobacterium tuberculosis H37Rv: an *AroQ Enzyme Not Regulated by the Aromatic Amino Acids 
Journal of Bacteriology  2006;188(24):8638-8648.
The gene Rv1885c from the genome of Mycobacterium tuberculosis H37Rv encodes a monofunctional and secreted chorismate mutase (*MtCM) with a 33-amino-acid cleavable signal sequence; hence, it belongs to the *AroQ class of chorismate mutases. Consistent with the heterologously expressed *MtCM having periplasmic destination in Escherichia coli and the absence of a discrete periplasmic compartment in M. tuberculosis, we show here that *MtCM secretes into the culture filtrate of M. tuberculosis. *MtCM functions as a homodimer and exhibits a dimeric state of the protein at a concentration as low as 5 nM. *MtCM exhibits simple Michaelis-Menten kinetics with a Km of 0.5 ± 0.05 mM and a kcat of 60 s−1 per active site (at 37°C and pH 7.5). The crystal structure of *MtCM has been determined at 1.7 Å resolution (Protein Data Bank identifier 2F6L). The protein has an all alpha-helical structure, and the active site is formed within a single chain without any contribution from the second chain in the dimer. Analysis of the structure shows a novel fold topology for the protein with a topologically rearranged helix containing Arg134. We provide evidence by site-directed mutagenesis that the residues Arg49, Lys60, Arg72, Thr105, Glu109, and Arg134 constitute the catalytic site; the numbering of the residues includes the signal sequence. Our investigation on the effect of phenylalanine, tyrosine, and tryptophan on *MtCM shows that *MtCM is not regulated by the aromatic amino acids. Consistent with this observation, the X-ray structure of *MtCM does not have an allosteric regulatory site.
PMCID: PMC1698256  PMID: 17146044
4.  Overproduction, purification, crystallization and preliminary X-ray diffraction studies of the human spliceosomal protein TXNL4B 
Human spliceosomal protein TXNL4B was purified and crystallized.
The human gene coding for the spliceosomal protein thioredoxin-like 4B (TXNL4B) was overexpressed in Escherichia coli and the encoded protein was purified and crystallized. Well diffracting single crystals were obtained by the vapor-diffusion method in hanging drops. The crystals belong to the primitive monoclinic space group P2, with unit-cell parameters a = 39.0, b = 63.6, c = 51.0 Å, β = 92.484°, and diffract to at least 1.50 Å. A SeMet derivative of the protein was prepared and crystallized for MAD phasing.
PMCID: PMC1952293  PMID: 16511018
spliceosomal proteins; thioredoxin-like 4B; Dim1; dim2; DLP
5.  Crystal Structure of the YgfZ Protein from Escherichia coli Suggests a Folate-Dependent Regulatory Role in One-Carbon Metabolism 
Journal of Bacteriology  2004;186(21):7134-7140.
The ygfZ gene product of Escherichia coli represents a large protein family conserved in bacteria to eukaryotes. The members of this family are uncharacterized proteins with marginal sequence similarity to the T-protein (aminomethyltransferase) of the glycine cleavage system. To assist with the functional assignment of the YgfZ family, the crystal structure of the E. coli protein was determined by multiwavelength anomalous diffraction. The protein molecule has a three-domain architecture with a central hydrophobic channel. The structure is very similar to that of bacterial dimethylglycine oxidase, an enzyme of the glycine betaine pathway and a homolog of the T-protein. Based on structural superposition, a folate-binding site was identified in the central channel of YgfZ, and the ability of YgfZ to bind folate derivatives was confirmed experimentally. However, in contrast to dimethylglycine oxidase and T-protein, the YgfZ family lacks amino acid conservation at the folate site, which implies that YgfZ is not an aminomethyltransferase but is likely a folate-dependent regulatory protein involved in one-carbon metabolism.
PMCID: PMC523196  PMID: 15489424
6.  Crystal structure of Escherichia coli protein ybgI, a toroidal structure with a dinuclear metal site 
The protein encoded by the gene ybgI was chosen as a target for a structural genomics project emphasizing the relation of protein structure to function.
The structure of the ybgI protein is a toroid composed of six polypeptide chains forming a trimer of dimers. Each polypeptide chain binds two metal ions on the inside of the toroid.
The toroidal structure is comparable to that of some proteins that are involved in DNA metabolism. The di-nuclear metal site could imply that the specific function of this protein is as a hydrolase-oxidase enzyme.
PMCID: PMC239858  PMID: 14519207
7.  Crystal Structure of the YchF Protein Reveals Binding Sites for GTP and Nucleic Acid 
Journal of Bacteriology  2003;185(14):4031-4037.
The bacterial protein encoded by the gene ychF is 1 of 11 universally conserved GTPases and the only one whose function is unknown. The crystal structure determination of YchF was sought to help with the functional assignment of the protein. The YchF protein from Haemophilus influenzae was cloned and expressed, and the crystal structure was determined at 2.4 Å resolution. The polypeptide chain is folded into three domains. The N-terminal domain has a mononucleotide binding fold typical for the P-loop NTPases. An 80-residue domain next to it has a pronounced α-helical coiled coil. The C-terminal domain features a six-stranded half-barrel that curves around an α-helix. The crablike three-domain structure of YchF suggests the binding site for a double-stranded nucleic acid in the cleft between the domains. The structure of the putative GTP-binding site is consistent with the postulated guanine specificity of the protein. Fluorescence measurements have demonstrated the ability of YchF to bind a double-stranded nucleic acid and GTP. Taken together with other experimental data and genomic analysis, these results suggest that YchF may be part of a nucleoprotein complex and may function as a GTP-dependent translation factor.
PMCID: PMC164861  PMID: 12837776

Results 1-7 (7)