title: A C-helix residue, Arg-123, has important roles in both the active and inactive forms of the cAMP receptor protein.
abstract: The cAMP receptor protein (CRP) of Escherichia coli exists in an equilibrium between active and inactive forms, and the effector, cAMP, shifts that equilibrium to the active form, thereby allowing DNA binding. For this equilibrium shift, a C-helix repositioning around the C-helix residues Thr-127 and Ser-128 has been reported as a critical local event along with proper beta4/beta5 positioning. Here we show that another C-helix residue, Arg-123, has a unique role in cAMP-dependent CRP activation in two different ways. First, Arg-123 is important for proper cAMP affinity, although it is not critical for the conformational change with saturating amounts of cAMP. Second, Arg-123 is optimal for stabilizing the inactive conformation of CRP when cAMP is absent, thereby allowing a maximal range of regulation by cAMP. However, Arg-123 does not appear to be critical for a functional response to cAMP, as has been proposed previously (Berman, H. M., Ten Eyck, L. F., Goodsell, D. S., Haste, N. M., Korney, A., and Taylor, S. S. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 45-50). Based on mutagenic evidence, we also propose the basis for the stabilization of the inactive form to be through a salt interaction between Asp-68 and Arg-123.
authors.affiliation: Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Hwan
authors.initials: H
authors.lastname: Youn
authors.forename: Robert L
authors.initials: RL
authors.lastname: Kerby
authors.forename: Junseock
authors.initials: J
authors.lastname: Koh
authors.forename: Gary P
authors.initials: GP
authors.lastname: Roberts
mesh_terms: D001120:Arginine / Q000737:chemistry / Q000502:physiology*; D001216:Asparagine / Q000737:chemistry; D000242:Cyclic AMP / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*
chemical_list: D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C481662:crp protein, E coli; D001216:Asparagine; D001120:Arginine; D000242:Cyclic AMP