Type III Pyridoxal 5-phosphate (PLP)-Dependent Enzymes Similar to D-Serine Dehydratase and D-Threonine Aldolase
This family includes eukaryotic D-serine dehydratases (DSD), cryptic DSDs from bacteria, D-threonine aldolases (D-TA), low specificity D-TAs, and similar uncharacterized proteins. DSD catalyzes the dehydration of D-serine to aminoacrylate, which is rapidly hydrolyzed to pyruvate and ammonia. D-TA reversibly catalyzes the aldol cleavage of D-threonine into glycine and acetaldehyde, and the synthesis of D-threonine from glycine and acetaldehyde. Members of this family are fold type III PLP-dependent enzymes, similar to bacterial alanine racemase (AR), which contains an N-terminal PLP-binding TIM barrel domain and a C-terminal beta-sandwich domain. AR exists as homodimers with active sites that lie at the interface between the TIM barrel domain of one subunit and the beta-sandwich domain of the other subunit. Based on similarity to AR, it is possible members of this family also form dimers in solution.