title: A polypeptide binding conformation of calreticulin is induced by heat shock, calcium depletion, or by deletion of the C-terminal acidic region.
abstract: It is widely believed that the chaperone activity of calreticulin is mediated by its ability to bind glycoproteins containing monoglucosylated oligosaccharides. However, calreticulin is also a polypeptide binding protein. Here we show that heat shock, calcium depletion, or deletion of the C-terminal acidic domain enhance binding of purified calreticulin to polypeptide substrates and enhance calreticulin's chaperone activity. These conditions also enhance calreticulin oligomerization, but oligomerization per se is not required for enhanced polypeptide binding. In cells, calreticulin oligomerization intermediates accumulate in response to conditions that induce protein misfolding (heat shock and tunicamycin treatments), and upon calcium depletion. Additionally, in cells, calreticulin binds to deglycosylated major histocompatibility complex class I heavy chains when significant levels of calreticulin oligomerization intermediates are induced. Thus, cell stress conditions that generate nonnative substrates of calreticulin also affect the conformational properties of calreticulin itself, and enhance its binding to substrates, independent of substrate glucosylation.
authors.affiliation: Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors.forename: Syed Monem
authors.initials: SM
authors.lastname: Rizvi
authors.forename: Laura
authors.initials: L
authors.lastname: Mancino
authors.forename: Vilasack
authors.initials: V
authors.lastname: Thammavongsa
authors.forename: Richard Louis
authors.initials: RL
authors.lastname: Cantley
authors.forename: Malini
authors.initials: M
authors.lastname: Raghavan
mesh_terms: D000595:Amino Acid Sequence; D024342:Amino Acids, Acidic; D002118:Calcium / Q000378:metabolism*; D037282:Calreticulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D006367:HeLa Cells; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000235:genetics; D017384:Sequence Deletion; D013379:Substrate Specificity; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D024342:Amino Acids, Acidic; D037282:Calreticulin; D015395:Histocompatibility Antigens Class I; D018832:Molecular Chaperones; D014415:Tunicamycin; D002118:Calcium