Molecular cloning, sequence and characterization of a novel streptococcal phosphoglycerate dehydrogenase gene.

The nucleotide sequence of a Streptococcus mutans serA gene that encodes D-3-phosphoglycerate dehydrogenase has been determined. The gene consisted of 1308-bp nucleotides coding for a 436-amino-acid polypeptide (48,546 Da). The deduced amino acid sequence showed a 66% identity with SerA from Bacillus subtilis and possessed specific residues (G-R-P-N-V-G) in the coenzyme-binding domain, alpha B helix. Recombinant streptococcal SerA was expressed using pMAL-c2 expression vector and purified by amylose resin affinity chromatography and DEAE-Sephacel column chromatography. This SerA enzyme catalyzed detectable reduction of alpha-ketoglutarate to 2-hydroxyglutaric acid. These findings indicate that the novel streptococcal phosphoglycerate dehydrogenase, SerA, is a member of a D-isomer-specific family of 2-hydroxyacid dehydrogenases.