A polypeptide binding conformation of calreticulin is induced by heat shock, calcium depletion, or by deletion of the C-terminal acidic region.
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.
Rizvi
Syed Monem
SM
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Mancino
Laura
L
Thammavongsa
Vilasack
V
Cantley
Richard Louis
RL
Raghavan
Malini
M
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
D024342:Amino Acids, Acidic; D037282:Calreticulin; D015395:Histocompatibility Antigens Class I; D018832:Molecular Chaperones; D014415:Tunicamycin; D002118:Calcium