title: Backbone dynamics of inactive, active, and effector-bound Cdc42Hs from measurements of (15)N relaxation parameters at multiple field strengths.
abstract: Cdc42Hs, a member of the Ras superfamily of GTP-binding proteins, initiates a cascade that begins with the activation of several kinases, including p21-activated kinase (PAK). We have previously determined the structure of Cdc42Hs and found that the regions involved in effector (Switch I) and regulator (Switch II) actions are partially disordered [Feltham, J. L., et al. (1997) Biochemistry 36, 8755-8766]. Recently, we used a 46-amino acid fragment of PAK (PBD46) to define the binding surface on Cdc42Hs, which includes the beta2 strand and a portion of Switch I [Guo, W., et al. (1998) Biochemistry 37, 14030-14037]. Here we describe the backbone dynamics of three constructs of [(15)N]Cdc42Hs (GDP-, GMPPCP-, and GMPPCP- and PBD46-bound) using (15)N-(1)H NMR measurements of T(1), T(1)(rho), and the steady-state NOE at three magnetic field strengths. Residue-specific values of the generalized order parameters (S(s)(2) and S(f)(2)), local correlation time (tau(e)), and exchange rate (R(ex)) were obtained using the Lipari-Szabo model-free formalism. Residues in Switch I were found to exhibit high-amplitude (low-order) motions on a nanosecond time scale, whereas those in Switch II experience low-amplitude motion on the nanosecond time scale and chemical (conformational) exchange on a millisecond time scale. The Insert region of Cdc42Hs-GDP exhibits high-order, nanosecond motions; the time scale of motion in the Insert is reduced in Cdc42Hs-GMPPCP and Cdc42Hs-PBD46. Overall, significant flexibility was observed mainly in the regions of Cdc42Hs that are involved in protein-protein interactions (Switch I, Switch II, and Insert), and flexibility was reduced upon interaction with a protein ligand. These results suggest that protein flexibility is important for high-affinity binding interactions.
authors.affiliation: Department of Chemistry, University of Wisconsin-La Crosse, La Crosse, Wisconsin 54601, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Loh
authors.forename: W
authors.initials: W
authors.lastname: Guo
authors.forename: L K
authors.initials: LK
authors.lastname: Nicholson
authors.forename: R E
authors.initials: RE
authors.lastname: Oswald
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000737:chemistry*; D019204:GTP-Binding Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D011522:Protons; D020764:cdc42 GTP-Binding Protein
chemical_list: D018797:Cell Cycle Proteins; D009587:Nitrogen Isotopes; D011522:Protons; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein