Type III Pyridoxal 5-phosphate (PLP)-Dependent Enzymes, Ornithine and Diaminopimelate Decarboxylases, and Related Enzymes
This family includes eukaryotic ornithine decarboxylase (ODC, EC 18.104.22.168), diaminopimelate decarboxylase (DapDC, EC 22.214.171.124), plant and prokaryotic biosynthetic arginine decarboxylase (ADC, EC 126.96.36.199), carboxynorspermidine decarboxylase (CANSDC), and ODC-like enzymes from diverse bacterial species. These proteins are fold type III PLP-dependent enzymes that catalyze essential steps in the biosynthesis of polyamine and lysine. ODC and ADC participate in alternative pathways of the biosynthesis of putrescine, which is the precursor of aliphatic polyamines in many organisms. ODC catalyzes the direct synthesis of putrescine from L-ornithine, while ADC converts L-arginine to agmatine, which is hydrolysed to putrescine by agmatinase in a pathway that exists only in plants and bacteria. DapDC converts meso-2,6-diaminoheptanedioate to L-lysine, which is the final step of lysine biosynthesis. CANSDC catalyzes the decarboxylation of carboxynorspermidine, which is the last step in the synthesis of norspermidine. The PLP-dependent decarboxylases in this family contain an N-terminal PLP-binding TIM-barrel domain and a C-terminal beta-sandwich domain, similar to bacterial alanine racemases. They exist 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. Prokaryotic ornithine, lysine and biodegradative arginine decarboxylases are fold type I PLP-dependent enzymes and are not included in this family.