The cyclic N-Acetyl-L-glutamate kinase (NAGK-C) catalyzes the phosphorylation of the gamma-COOH group of N-acetyl-L-glutamate (NAG) by ATP in the second step of arginine biosynthesis found in some bacteria and photosynthetic organisms using the non-acetylated, cyclic route of ornithine biosynthesis. In this pathway, glutamate is first N-acetylated and then phosphorylated by NAGK to give phosphoryl NAG, which is converted to NAG-ornithine. There are two variants of the arginine biosynthesis pathway. In the cyclic one, typified by Thermotoga maritima and Pseudomonas aeruginosa, the acetyl group is recycled by reversible transacetylation from acetylornithine to glutamate. The phosphorylation of NAG by NAGK is feedback inhibited by arginine. In photosynthetic organisms, NAGK is the target of the nitrogen-signaling protein PII. Hexameric formation of NAGK domains appears to be essential to both arginine inhibition and NAGK-PII complex formation [, , , , , , ].
This entry represents N-acetyl-D-glucosamine kinases which catalyse the phosphorylation of N-acetyl-D-glucosamine (GlcNAc) derived from cell-wall degradation, yielding GlcNAc-6-P [, ]. This group of proteins belong to the NagK subfamily of the ROK (nagC/xylR) family.
This entry includes N-acetyl-D-glucosamine kinases (NAGKs) from prokaryotes and eukaryotes. NAGK converts endogenous N-acetylglucosamine (GlcNAc), a major component of complex carbohydrates, from lysosomal degradation or nutritional sources into GlcNAc 6-phosphate []. It has been shown to play an enzyme activity-independent role in human neurons [, ].
The N-Acetyl-L-glutamate kinase (NAGK) of the fungal arginine-biosynthetic pathway (fArgBP) is a nuclear-encoded, mitochondrial polyprotein precursor with an N-terminal NAGK (ArgB) domain (this entry), a central DUF619 domain, and a C-terminal reductase domain (ArgC, N-Acetylglutamate Phosphate Reductase, NAGPR). The precursor is cleaved in the mitochondria into two distinct enzymes (NAGK-DUF619 and NAGPR). Native molecular weights of these proteins indicate that the kinase is an octamer whereas the reductase is a dimer. This entry also includes some gamma-proteobacteria (Xanthomonas and Xylella) NAG kinases with an N-terminal NAGK (ArgB) domain and a C-terminal DUF619 domain. The DUF619 domain is described as a putative distant homologue of the acetyltransferase, ArgA, predicted to function in NAG synthase association in fungi. Eukaryotic sequences have an N-terminal mitochondrial transit peptide [,, ].
The noncyclic N-Acetyl-L-glutamate kinase (NAGK-NC) catalyzes the phosphorylation of the gamma-COOH group of N-acetyl-L-glutamate (NAG) by ATP in the second step of microbial arginine biosynthesis using the acetylated, noncyclic route of ornithine biosynthesis. There are two variants of the arginine biosynthesis pathway. In this one, typified by the pathway in Escherichia coli, glutamate is acetylated by acetyl-CoA and acetylornithine is deacylated hydrolytically. In this pathway, feedback inhibition by arginine occurs at the initial acetylation of glutamate and not at the phosphorylation of NAG by NAGK. The Escherichia coli NAGK is a homodimer [, , , , , ].
