title: Role of electrostatic interactions in PDZ domain ligand recognition.
abstract: PDZ domains are protein-protein interaction modules that normally recognize short C-terminal peptides. The apparent requirement for a ligand with a free terminal carboxylate group has led to the proposal that electrostatic interactions with the terminus play a significant role in recognition. However, this model has been called into question by the more recent finding that PDZ domains can recognize some internal peptide motifs that occur within a specific secondary structure context. Although these motifs bind at the same interface, they lack a terminal charge. Here we have investigated the role of electrostatics in PDZ-mediated recognition in the mouse alpha1-syntrophin PDZ domain by examining the salt dependence of binding to both terminal and internal ligands and the effects of mutating a conserved basic residue previously proposed to play a role in electrostatic recognition. These studies indicate that direct electrostatic interactions with the peptide terminus do not play a significant energetic role in binding. Additional chemical modification studies of the peptide terminus support a model in which steric and hydrogen bonding complementarity play a primary role in recognition specificity. Peptides with a free carboxy terminus, or presented within a specific structural context, can satisfy these requirements.
authors.affiliation: Program in Biological Sciences, Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143, USA.
authors.forename: Baruch Z
authors.initials: BZ
authors.lastname: Harris
authors.forename: Francis W
authors.initials: FW
authors.lastname: Lau
authors.forename: Naoaki
authors.initials: N
authors.lastname: Fujii
authors.forename: R Kiplin
authors.initials: RK
authors.lastname: Guy
authors.forename: Wendell A
authors.initials: WA
authors.lastname: Lim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002135:Calcium-Binding Proteins; D017124:Conserved Sequence / Q000235:genetics; D006860:Hydrogen Bonding; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D002135:Calcium-Binding Proteins; D008024:Ligands; D008565:Membrane Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; C033652:postsynaptic density proteins; C091825:syntrophin alpha1