InterPro domain: IPR005260

Aspartate kinase catalyzes the first step in the biosynthesis of Lys (via its precursor diaminopimelate), Met, and Thr. In Escherichia coli, a distinct isozyme is inhibited by each of these three amino acid end products [ 1 ]. The Met-sensitive (I) and Thr-sensitive (II) forms are bifunctional enzymes fused to homoserine dehydrogenase, which catalyses the next step in the biosynthesis of these amino acids. In contrast, the Lys-sensitive form (III) is a monofunctional enzyme; homoserine dehydrogenase is not part of the Lys biosynthetic pathway.

This entry describes a subclass of the aspartate kinases that are mostly Lys-sensitive and are not fused to homoserine dehydrogenase. The E. coli enzyme is a homodimer, while the Bacillus and Corynebacterium enzymes are alpha 2/beta 2 heterotetramers, where the beta subunit is translated from an in-phase alternative initiator at Met-246 [ 2 , 3 ]. 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.

1. Mutational analysis of the feedback sites of lysine-sensitive aspartokinase of Escherichia coli. FEMS Microbiol. Lett. 173, 211-5
2. Aspartokinase II from Bacillus subtilis is degraded in response to nutrient limitation. J. Biol. Chem. 265, 14947-55
3. Gene structure and expression of the Corynebacterium flavum N13 ask-asd operon. J. Bacteriol. 175, 4096-103