Attempts to characterize the structure and molecular chaperone functions of calnexin in vitro

grantor: University of TorontoClass I molecules are composed of three subunits, an integral membrane glycoprotein referred to as the heavy chain, a soluble noncovalently associated protein referred to as ß2m, and an 8 to 10 amino acid peptide fragment. These molecules function on the cell surface to display peptide fragments from the degradation of cytosolic proteins. They are scrutinized by cytotoxic T lymphocytes to assist in the detection of viral infection. The molecular chaperone calnexin is intimately involved in the biogenesis of class I molecules. Although calnexin release from folding proteins is frequently correlative with folding or assembly events, the event that results in the dissociation of calnexin from class I remains elusive. It is suspected that binding of the peptide fragment to the class I heavy chain-ß2m heterodimer triggers this release since the association is prolonged in the absence of peptide. Furthermore, peptide binding causes the release of another molecule that binds to class 1, the transporter responsible for translocating these peptides, TAP. This thesis attempts to further address the issue of what triggers calnexin release from class I heavy chains using a number of ' in vitro' systems that reconstitute both calnexin interactions and assembly of class I subunits. (Abstract shortened by UMI.)M.Sc