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Putative D-3-Phosphoglycerate Dehydrogenases Phosphoglycerate dehydrogenases (PGDHs) catalyze the initial step in the biosynthesis of L-serine from D-3-phosphoglycerate. PGDHs come in 3 distinct structural forms, with this first group being related to 2-hydroxy acid dehydrogenases, sharing structural similarity to formate and glycerate dehydrogenases of the D-specific 2-hydroxyacid dehydrogenase superfamily, which also include groups such as L-alanine dehydrogenase and S-adenosylhomocysteine hydrolase. Despite often low sequence identity, these proteins typically have a characteristic arrangement of 2 similar subdomains of the alpha/beta Rossmann fold NAD+ binding form. The NAD+ binding domain is inserted within the linear sequence of the mostly N-terminal catalytic domain, which has a similar domain structure to the internal NAD binding domain. Structurally, these domains are connected by extended alpha helices and create a cleft in which NAD is bound, primarily to the C-terminal portion of the 2nd (internal) domain. Some related proteins have similar structural subdomain but with a tandem arrangement of the catalytic and NAD-binding subdomains in the linear sequence. Many, not all, members of this family are dimeric.
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