title: The myosin-binding UCS domain but not the Hsp90-binding TPR domain of the UNC-45 chaperone is essential for function in Caenorhabditis elegans.
abstract: The UNC-45 family of molecular chaperones is expressed in metazoan organisms from Caenorhabditis elegans to humans. The UNC-45 protein is essential in C. elegans for early body-wall muscle cell development and A-band assembly. We show that the myosin-binding UCS domain of UNC-45 alone is sufficient to rescue lethal unc-45 null mutants arrested in embryonic muscle development and temperature-sensitive loss-of-function unc-45 mutants defective in worm A-band assembly. Removal of the Hsp90-binding TPR domain of UNC-45 does not affect rescue. Similar results were obtained with overexpression of the same fragments in wild-type nematodes when assayed for diminution of myosin accumulation and assembly. Titration experiments show that, on a per molecule basis, UCS has greater activity in C. elegans muscle in vivo than full-length UNC-45 protein, suggesting that UNC-45 is inhibited by either the TPR domain or its interaction with the general chaperone Hsp90. In vitro experiments with purified recombinant C. elegans Hsp90 and UNC-45 proteins show that they compete for binding to C. elegans myosin. Our in vivo genetic and in vitro biochemical experiments are consistent with a novel inhibitory role for Hsp90 with respect to UNC-45 action.
authors.affiliation: Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX 77555, USA.
authors.forename: Weiming
authors.initials: W
authors.lastname: Ni
authors.forename: Alex H
authors.initials: AH
authors.lastname: Hutagalung
authors.forename: Shumin
authors.initials: S
authors.lastname: Li
authors.forename: Henry F
authors.initials: HF
authors.lastname: Epstein
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001667:Binding, Competitive; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009043:Motor Activity / Q000235:genetics; D024510:Muscle Development; D009154:Mutation / Q000235:genetics; D009218:Myosins / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D055503:Protein Multimerization / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism / Q000473:pathology
chemical_list: D029742:Caenorhabditis elegans Proteins; D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; C107348:unc-45 protein, C elegans; D009218:Myosins