title: Active participation of Hsp90 in the biogenesis of the trimeric reovirus cell attachment protein sigma1.
abstract: The reovirus cell attachment protein, sigma1, is a lollipop-shaped homotrimer with an N-terminal fibrous tail and a C-terminal globular head. Biogenesis of this protein involves two trimerization events: N-terminal trimerization, which occurs cotranslationally and is Hsp70/ATP-independent, and C-terminal trimerization, which occurs posttranslationally and is Hsp70/ATP-dependent. To determine if Hsp90 also plays a role in sigma1 biogenesis, we analyzed sigma1 synthesized in rabbit reticulocyte lysate. Coprecipitation experiments using anti-Hsp90 antibodies revealed that Hsp90 was associated with immature sigma1 trimers (hydra-like intermediates with assembled N termini and unassembled C termini) but not with mature trimers. The use of truncated sigma1 further demonstrated that only the C-terminal half of sigma1 associated with Hsp90. In the presence of the Hsp90 binding drug geldanamycin, N-terminal trimerization proceeded normally, but C-terminal trimerization was blocked. Geldanamycin did not inhibit the association of Hsp90 with sigma 1 but prevented the subsequent release of Hsp90 from the immature sigma1 complex. We also examined the status of p23, an Hsp90-associated cochaperone. Like Hsp90, p23 only associated with immature sigma1 trimers, and this association was mapped to the C-terminal half of sigma1. However, unlike Hsp90, p23 was released from the sigma1 complex upon the addition of geldanamycin. These results highlight an all-or-none concept of chaperone involvement in different oligomerization domains within a single protein and suggest a possible common usage of chaperones in the regulation of general protein folding and of steroid receptor activation.
authors.affiliation: Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Centre, Calgary, Alberta, Canada T2N 4N1.
authors.forename: R
authors.initials: R
authors.lastname: Gilmore
authors.forename: M C
authors.initials: MC
authors.lastname: Coffey
authors.forename: P W
authors.initials: PW
authors.lastname: Lee
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D016227:Benzoquinones; D036022:Capsid Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D047029:Lactams, Macrocyclic; D018832:Molecular Chaperones / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D014176:Protein Biosynthesis / Q000235:genetics; D017510:Protein Folding; D011809:Quinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D017384:Sequence Deletion; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: D016227:Benzoquinones; D036022:Capsid Proteins; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D018832:Molecular Chaperones; D011809:Quinones; D012333:RNA, Messenger; D014764:Viral Proteins; C031728:sigma 1 protein, reovirus; D000255:Adenosine Triphosphate; C001277:geldanamycin