The crystal structure of methylglyoxal synthase from Escherichia coli.
BACKGROUND
The reaction mechanism of methylglyoxal synthase (MGS) is believed to be similar to that of triosephosphate isomerase (TIM). Both enzymes utilise dihydroxyacetone phosphate (DHAP) to form an enediol(ate) phosphate intermediate as the first step of their reaction pathways. However, the second catalytic step in the MGS reaction pathway is characterized by the elimination of phosphate and collapse of the enediol(ate) to form methylglyoxal instead of reprotonation to form the isomer glyceraldehyde 3-phosphate.


RESULTS
The crystal structure of MGS bound to formate and substoichiometric amounts of phosphate in the space group P6522 has been determined at 1.9 A resolution. This structure shows that the enzyme is a homohexamer composed of interacting five-stranded beta/alpha proteins, rather than the hallmark alpha/beta barrel structure of TIM. The conserved residues His19, Asp71, and His98 in each of the three monomers in the asymmetric unit bind to a formate ion that is present in the crystallization conditions. Differences in the three monomers in the asymmetric unit are localized at the mouth of the active site and can be ascribed to the presence or absence of a bound phosphate ion.


CONCLUSIONS
In agreement with site-directed mutagenesis and mechanistic enzymology, the structure suggests that Asp71 acts as the catalytic base. Further, Asp20 and Asp101 are involved in intersubunit salt bridges. These salt bridges may provide a pathway for transmitting allosteric information.
Saadat
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Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
Harrison
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D000494:Allosteric Regulation; D000495:Allosteric Site; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D019757:Carbon-Oxygen Lyases / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010710:Phosphates / Q000378:metabolism; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry
D001426:Bacterial Proteins; D010710:Phosphates; D011993:Recombinant Fusion Proteins; D019757:Carbon-Oxygen Lyases; C021578:methylglyoxal synthase