STRUCTURAL STUDIES ON AHRC, THE ARGININE REPRESSOR/ACTIVATOR PROTEIN FROM BACILLUS SUBTILIS

Caitriona Dennis¹, Nicholas Glycos^1,2, Mark Parsons¹ and Simon Phillips¹

¹School of Biochemistry and Molecular Biology, University of Leeds, Leeds, LS2 9JT, United Kingdom
²IMBB, PO BOX 1527, 71110 Heraklion, Crete, Greece

AhrC is a site-specific DNA-binding protein from B. subtilis which controls the concentration of the amino acid arginine. In response to elevated concentration of L-arginine, AhrC both represses the transcription of arginine biosynthetic genes and activates transcription of arginine catabolic genes.Unusually for a DNA-binding protein, AhrC is a hexamer and is proposed to interact with one, two or three DNA recognition sequences within the control regions of arginine biosynthetic and catabolic genes.

Crystals of AhrC, both alone and with bound arginine, have been prepared. The crystals are orthorhombic and have one hexamer in the asymmetric unit. The hexamer is made up of 6 monomers containing 2 domains - an oligomerisation domain and a DNA-binding domain. Attempts to find heavy atom derivatives have been, so far, unsuccessful. The hexameric core structure (oligomerisation domains) from ArgR, a homologous protein from E.coli, has been used as a trial model for Molecular Replacement. Using AMoRe, a solution has been obtained. Refinement of this structure is currently underway.