In molecular biology, the arginine repressor (ArgR) is a repressor of prokaryotic arginine deiminase pathways.
The arginine dihydrolase (AD) pathway is found in many prokaryotes and some eukaryotes, an example of the latter being Giardia lamblia (Giardia intestinalis).[1] The three-enzyme anaerobic pathway breaks down L-arginine to form 1 mol of ATP, carbon dioxide and ammonia. In some bacteria, the first enzyme, arginine deiminase, can account for up to 10% of total cellprotein.[1]
Most prokaryotic arginine deiminase pathways are under the control of a repressor gene, termed ArgR.[2] This is a negative regulator, and will only release the arginine deiminase operon for expression in the presence of arginine.[3] The crystal structure of apo-ArgR from Bacillus stearothermophilus has been determined to 2.5A by means of X-ray crystallography.[4] The protein exists as a hexamer of identical subunits, and is shown to have six DNA-binding domains, clustered around a central oligomeric core when bound to arginine. It predominantly interacts with A.T residues in ARG boxes. This hexameric protein binds DNA at its N terminus to repress arginine biosynthesis or activate arginine catabolism. Some species have several ArgR paralogs. In a neighbour-joining tree, some of these paralogoussequences show long branches and differ significantly from the well-conserved C-terminal region.
^ abBrown DM, Upcroft JA, Edwards MR, Upcroft P (January 1998). "Anaerobic bacterial metabolism in the ancient eukaryote Giardia duodenalis". Int. J. Parasitol. 28 (1): 149–64. doi:10.1016/S0020-7519(97)00172-0. PMID9504342.
^Lu CD, Houghton JE, Abdelal AT (May 1992). "Characterization of the arginine repressor from Salmonella typhimurium and its interactions with the carAB operator". J. Mol. Biol. 225 (1): 11–24. doi:10.1016/0022-2836(92)91022-H. PMID1583685.