title: Structure of the periplasmic chaperone Skp suggests functional similarity with cytosolic chaperones despite differing architecture.
abstract: The 17-kDa protein (Skp) of Escherichia coli is a homotrimeric periplasmic chaperone for newly synthesized outer-membrane proteins. Here we present its X-ray structure at a resolution of 2.35 A. Three hairpin-shaped alpha-helical extensions reach out by approximately 60 A from a trimerization domain, which is composed of three intersubunit beta-sheets that wind around a central axis. The alpha-helical extensions approach each other at their distal turns, resulting in a fold that resembles a 'three-pronged grasping forceps'. The overall shape of Skp is reminiscent of the cytosolic chaperone prefoldin, although it is based on a radically different topology. The peculiar architecture, with apparent plasticity of the prongs and distinct electrostatic and hydrophobic surface properties, supports the recently proposed biochemical mechanism of this chaperone: formation of a Skp(3)-Omp complex protects the outer membrane protein from aggregation during passage through the bacterial periplasm.
authors.affiliation: Lehrstuhl für Biologische Chemie, Technische Universität München, 85350 Freising-Weihenstephan, Germany.
authors.forename: Ingo P
authors.initials: IP
authors.lastname: Korndörfer
authors.forename: Monica K
authors.initials: MK
authors.lastname: Dommel
authors.forename: Arne
authors.initials: A
authors.lastname: Skerra
mesh_terms: D000595:Amino Acid Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000502:physiology*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D019897:Periplasm / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017386:Sequence Homology, Amino Acid; D013499:Surface Properties
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; C072721:Skp protein, E coli