AAK_AK-HSDH-like: Amino Acid Kinase Superfamily (AAK), AK-HSDH-like; this family includes the N-terminal catalytic domain of aspartokinase (AK) of the bifunctional enzyme AK- homoserine dehydrogenase (HSDH). These aspartokinases are found in such bacteria as E. coli (AKI-HSDHI, ThrA and AKII-HSDHII, MetL) and in higher plants (Z. mays AK-HSDH). AK and HSDH are the first and third enzymes in the biosynthetic pathway of the aspartate family of amino acids. AK catalyzes the phosphorylation of Asp to P-aspartyl phosphate. HSDH catalyzes the NADPH-dependent conversion of Asp 3-semialdehyde to homoserine. ThrA and MetL are involved in threonine and methionine biosynthesis, respectively. In E. coli, ThrA is subject to allosteric regulation by the end product L-threonine and the native enzyme is reported to be tetrameric. As with bacteria, plant AK and HSDH are feedback inhibited by pathway end products. Maize AK-HSDH is a Thr-sensitive 180-kD enzyme. Arabidopsis AK-HSDH is an alanine-activated, threonine-sensitive enzyme whose ACT domains, located C-terminal to the AK catalytic domain, were shown to be involved in allosteric activation. Also included in this CD is the catalytic domain of the aspartokinase (AK) of the lysine-sensitive aspartokinase isoenzyme AKIII, a monofunctional class enzyme (LysC) found in some bacteria such as E. coli. In E. coli, LysC is reported to be a homodimer of 50 kD subunits. Also included in this CD is the catalytic domain of aspartokinase (AK) of the bifunctional enzyme AK - DAP decarboxylase (DapDC) found in some bacteria. DapDC, which is the lysA gene product, catalyzes the decarboxylation of DAP to lysine.
Jiyao W et al.(2023). "The conserved domain database in 2023.",