Dihydropicolinate synthase (DHDPS) is the key enzyme in lysine biosynthesisvia the diaminopimelate pathway of prokaryotes, some phycomycetes andhigher plants. The enzyme catalyses the condensation of L-aspartate-beta-semialdehyde and pyruvate to dihydropicolinic acid via a ping-pongmechanism in which pyruvate binds to the enzyme by forming a Schiff-basewith a lysine residue [<cite idref="PUB00003343"/>]. Three other proteins are structurally related to DHDPS and probably also actvia a similar catalytic mechanism. These are <taxon tax_id="562">Escherichia coli</taxon> N-acetylneuraminate lyase (<db_xref db="EC" dbkey="4.1.3.3"/>) (gene nanA), which catalyzes the condensation of N-acetyl-D-mannosamine and pyruvate to form N-acetylneuraminate; <taxon tax_id="382">Rhizobium meliloti</taxon> (Sinorhizobium meliloti) protein mosA [<cite idref="PUB00002226"/>], which is involved in the biosynthesis of the rhizopine 3-o-methyl-scyllo-inosamine; and E. coli hypothetical protein yjhH.The sequences of DHDPS from different sources are well-conserved. Thestructure takes the form of a homotetramer, in which 2 monomers arerelated by an approximate 2-fold symmetry [<cite idref="PUB00003343"/>]. Each monomer comprises2 domains: an 8-fold alpha-/beta-barrel, and a C-terminal alpha-helicaldomain. The fold resembles that of N-acetylneuraminate lyase. The activesite lysine is located in the barrel domain, and has access via 2 channelson the C-terminal side of the barrel.<p>This pattern signature contains a lysine residue which has been shown, in the <taxon tax_id="562">Escherichia coli</taxon> enzyme DapA [<cite idref="PUB00000520"/>], to be the one that forms a Schiff-base with the substrate. </p>