This model describes a subclass of aspartate kinases. These are mostly Lys-sensitive and not fused to homoserine dehydrogenase, unlike some Thr-sensitive and Met-sensitive forms. Homoserine dehydrogenase is part of Thr and Met but not Lys biosynthetic pathways. Aspartate kinase catalyzes a first step in the biosynthesis from Asp of Lys (and its precursor diaminopimelate), Met, and Thr. In E. coli, a distinct isozyme is inhibited by each of the three amino acid products. The Met-sensitive (I) and Thr-sensitive (II) forms are bifunctional enzymes fused to homoserine dehydrogenases and form homotetramers, while the Lys-sensitive form (III) is a monofunctional homodimer. The Lys-sensitive enzyme of Bacillus subtilis resembles the E. coli form but is an alpha 2/beta 2 heterotetramer, where the beta subunit is translated from an in-phase alternative initiator at Met-246. The protein slr0657 from Synechocystis PCC6803 is extended by a duplication of the C-terminal region corresponding to the beta chain. Incorporation of a second copy of the C-terminal domain may be quite common in this subgroup of aspartokinases. [Amino acid biosynthesis, Aspartate family]
Jiyao W et al.(2023). "The conserved domain database in 2023.",