title: Analysis of protein hydration in ultrahigh-resolution structures of the SRP GTPase Ffh.
abstract: Two new structures of the SRP GTPase Ffh have been determined at 1.1 A resolution and provide the basis for comparative examination of the extensive water structure of the apo conformation of these GTPases. A set of well defined water-binding positions have been identified in the active site of the two-domain ;NG' GTPase, as well as at two functionally important interfaces. The water hydrogen-bonding network accommodates alternate conformations of the protein side chains by undergoing local rearrangements and, in one case, illustrates binding of a solute molecule within the active site by displacement of water molecules without further disruption of the water-interaction network. A subset of the water positions are well defined in several lower resolution structures, including those of different nucleotide-binding states; these appear to function in maintaining the protein structure. Consistent arrangements of surface water between three different ultrahigh-resolution structures provide a framework for beginning to understand how local water structure contributes to protein-ligand and protein-protein binding in the SRP GTPases.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Northwestern University, Chicago, IL 60611, USA.
authors.forename: Ursula D
authors.initials: UD
authors.lastname: Ramirez
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Freymann
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D004583:Electrons; D029968:Escherichia coli Proteins / Q000737:chemistry; D020558:GTP Phosphohydrolases / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D018271:Signal Recognition Particle / Q000737:chemistry*; D014867:Water / Q000032:analysis / Q000737:chemistry*
chemical_list: D029968:Escherichia coli Proteins; C082931:Ffh protein, E coli; D018271:Signal Recognition Particle; D014867:Water; D020558:GTP Phosphohydrolases