title: Binding of Crumbs to the Par-6 CRIB-PDZ Module Is Regulated by Cdc42.
abstract: Par-6 is a scaffold protein that organizes other proteins into a complex required to initiate and maintain cell polarity. Cdc42-GTP binds the CRIB module of Par-6 and alters the binding affinity of the adjoining PDZ domain. Allosteric regulation of the Par-6 PDZ domain was first demonstrated using a peptide identified in a screen of typical carboxyl-terminal ligands. Crumbs, a membrane protein that localizes a conserved polarity complex, was subsequently identified as a functional partner for Par-6 that likely interacts with the PDZ domain. Here we show by nuclear magnetic resonance that Par-6 binds a Crumbs carboxyl-terminal peptide and report the crystal structure of the PDZ-peptide complex. The Crumbs peptide binds Par-6 more tightly than the previously studied carboxyl peptide ligand and interacts with the CRIB-PDZ module in a Cdc42-dependent manner. The Crumbs:Par-6 crystal structure reveals specific PDZ-peptide contacts that contribute to its higher affinity and Cdc42-enhanced binding. Comparisons with existing structures suggest that multiple C-terminal Par-6 ligands respond to a common conformational switch that transmits the allosteric effects of GTPase binding.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States.
authors.forename: Dustin S
authors.initials: DS
authors.lastname: Whitney
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States.
authors.forename: Francis C
authors.initials: FC
authors.lastname: Peterson
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States.
authors.forename: Aaron W
authors.initials: AW
authors.lastname: Kittell
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States.
authors.forename: John M
authors.initials: JM
authors.lastname: Egner
authors.affiliation: Department of Chemistry and Biochemistry and Institute for Molecular Biology, University of Oregon , Eugene, Oregon 97403, United States.
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Prehoda
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin , Milwaukee, Wisconsin 53226, United States.
authors.forename: Brian F
authors.initials: BF
authors.lastname: Volkman
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D004331:Drosophila melanogaster; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D054731:PDZ Domains / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: C090145:Cdc42 protein, Drosophila; D029721:Drosophila Proteins; D008565:Membrane Proteins; C064360:crb protein, Drosophila; C532584:Par-6 protein, Drosophila; D011493:Protein Kinase C; D019204:GTP-Binding Proteins