AAK_AK-DapG-like: Amino Acid Kinase Superfamily (AAK), AK-DapG-like; this CD includes the N-terminal catalytic aspartokinase (AK) domain of the diaminopimelate-sensitive aspartokinase isoenzyme AKI (DapG), a monofunctional enzymes found in Bacilli (Bacillus subtilis 168), Clostridia, and Actinobacteria bacterial species, as well as, the catalytic AK domain of the lysine-sensitive aspartokinase isoenzyme AKII of Bacillus subtilis 168, the lysine plus threonine-sensitive aspartokinase of Corynebacterium glutamicum, and related isoenzymes. In Bacillus subtilis, the regulation of the diaminopimelate-lysine biosynthetic pathway involves dual control by diaminopimelate and lysine, effected through separate diaminopimelate- and lysine-sensitive aspartokinase isoenzymes. The role of the AKI isoenzyme is most likely to provide a constant level of aspartyl-beta-phosphate for the biosynthesis of diaminopimelate for peptidoglycan synthesis and dipicolinate during sporulation. The B. subtilis 168 AKII is induced by methionine, and repressed and inhibited by lysine. In Corynebacterium glutamicum and other various Gram-positive bacteria, the DAP-lysine pathway is feedback regulated by the concerted action of lysine and threonine. Also included in this CD are the aspartokinases of the extreme thermophile, Thermus thermophilus HB27, the Gram-negative obligate methylotroph, Methylophilus methylotrophus AS1, and those single aspartokinase isoenzyme types found in Pseudomonas, C. glutamicum, and Amycolatopsis lactamdurans. The B. subtilis AKI is tetrameric consisting of two alpha and two beta subunits; the alpha (43 kD) and beta (17 kD) subunit formed by two in-phase overlapping genes. The alpha subunit contains the AK catalytic domain and two ACT domains. The beta subunit contains two ACT domains. The B. subtilis 168 AKII aspartokinase is also described as tetrameric consisting of two alpha and two beta subunits. Some archeal aspartokinases in this group lack recognizable ACT domains.
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