Pyrimidine (PYR) binding domain of 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase (MenD) and related proteins.
Thiamine pyrophosphate (TPP family), pyrimidine (PYR) binding domain of 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate (SEPHCHC) synthase (MenD) subfamily. The PYR domain is found in many key metabolic enzymes which use TPP (also known as thiamine diphosphate) as a cofactor. TPP binds in the cleft formed by a PYR domain and a PP domain. The PYR domain, binds the aminopyrimidine ring of TPP, the PP domain binds the diphosphate residue. The PYR and PP domains have a common fold, but do not share strong sequence conservation. The PP domain is not included in this sub-family. Most TPP-dependent enzymes have the PYR and PP domains on the same subunit although these domains can be alternatively arranged in the primary structure. TPP-dependent enzymes are multisubunit proteins, the smallest catalytic unit being a dimer-of-active sites. Escherichia coli MenD (EcMenD) is a homotetramer (dimer-of-homodimers), having two active sites per homodimer lying between PYR and PP domains of different subunits. EcMenD catalyzes a Stetter-like conjugate addition of alpha-ketoglutarate to isochorismate, leading to the formation of SEPHCHC and carbon dioxide, this addition is the first committed step in the biosynthesis of vitamin K2 (menaquinone).