title: The N-terminus of the WD5 repeat of human RACK1 binds to airway epithelial NHERF1.
abstract: Regulation of the CFTR Cl channel function involves a protein complex of activated protein kinase Cepsilon (PKCepsilon) bound to RACK1, a receptor for activated C kinase, and RACK1 bound to the human Na(+)/H(+) exchanger regulatory factor (NHERF1) in human airway epithelial cells. Binding of NHERF1 to RACK1 is mediated via a NHERF1-PDZ1 domain. The goal of this study was to identify the binding motif for human NHERF1 on RACK1. We examined the site of binding of NHERF1 on RACK1 using peptides encoding the seven WD40 repeat units of human RACK1. One WD repeat peptide, WD5, directly binds NHERF1 and the PDZ1 domain with similar EC(50) values, blocks binding of recombinant RACK1 and NHERF1, and pulls down endogenous RACK1 from Calu-3 cell lysate in a dose-dependent manner. The remaining WD repeat peptides did not block RACK1-NHERF1 binding. An 11-amino acid peptide encoding a site on the PDZ1 domain blocks binding of the WD5 repeat peptide with the PDZ1 domain. An N-terminal 12-amino acid segment of the WD5 repeat peptide, which comprises the first of four antiparallel beta-strands, dose-dependently binds to the PDZ1 domain of NHERF1 and blocks binding of the PDZ1 domain to RACK1. These results suggest that the binding site might form a beta-turn with topology sufficient for binding of NHERF1. Our results also demonstrate binding of NHERF to RACK1 at the WD5 repeat, which is distinct from the PKCepsilon binding site on the WD6 repeat of RACK1.
authors.affiliation: Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio 44106-4948, USA. carole.liedtke@case.edu
authors.forename: Carole M
authors.initials: CM
authors.lastname: Liedtke
authors.forename: Xiangyun
authors.initials: X
authors.lastname: Wang
mesh_terms: D001665:Binding Sites; D002460:Cell Line; D002474:Cell-Free System / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012137:Respiratory System / Q000166:cytology / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D009363:Neoplasm Proteins; D010750:Phosphoproteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D051744:Protein Kinase C-epsilon; D019204:GTP-Binding Proteins