title: The structure of putative N-acetyl glutamate kinase from Thermus thermophilus reveals an intermediate active site conformation of the enzyme.
abstract: The de novo biosynthesis of arginine in microorganisms and plants is accomplished via several enzymatic steps. The enzyme N-acetyl glutamate kinase (NAGK) catalyzes the phosphorylation of the γ-COO(-) group of N-acetyl-L-glutamate (NAG) by adenosine triphosphate (ATP) which is the second rate limiting step in arginine biosynthesis pathway. Here we report the crystal structure of putative N-acetyl glutamate kinase (NAGK) from Thermus thermophilus HB8 (TtNAGK) determined at 1.92Å resolution. The structural analysis of TtNAGK suggests that the dimeric quaternary state of the enzyme and arginine insensitive nature are similar to mesophilic Escherichia coli NAGK. These features are significantly different from its thermophilic homolog Thermatoga maritima NAGK which is hexameric and arginine-sensitive. TtNAGK is devoid of its substrates but contains two sulfates at the active site. Very interestingly the active site of the enzyme adopts a conformation which is not completely open or closed and likely represents an intermediate stage in the catalytic cycle unlike its structural homologs, which all exist either in the open or closed conformation. Engineering arginine biosynthesis pathway enzymes for the production of l-arginine is an important industrial application. The structural comparison of TtNAGK with EcNAGK revealed the structural basis of thermostability of TtNAGK and this information could be very useful to generate mutants of NAGK with increased overall stability.
authors.affiliation: Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600 025, India.
authors.forename: Ramya
authors.initials: R
authors.lastname: Sundaresan
authors.forename: Preethi
authors.initials: P
authors.lastname: Ragunathan
authors.forename: Seiki
authors.initials: S
authors.lastname: Kuramitsu
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
authors.forename: Thirumananseri
authors.initials: T
authors.lastname: Kumarevel
authors.forename: Karthe
authors.initials: K
authors.lastname: Ponnuraj
mesh_terms: D001120:Arginine / Q000737:chemistry / Q000494:pharmacology; D020134:Catalytic Domain; D004795:Enzyme Stability; D025461:Feedback, Physiological; D006358:Hot Temperature; D017851:Phosphotransferases (Carboxyl Group Acceptor) / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D001120:Arginine; D017851:Phosphotransferases (Carboxyl Group Acceptor); C018721:acetylglutamate kinase