ER Protein folding processes do not work in isolation – they are co-ordinated: e.g., MHC Class I assembly

1.BiP maintains solubility of MHC Class I HC until β2 microglobulin binds. 2. and N-glycosylation allows entry into a folding environment 3. provided by the chaperone calreticulin 4. and its PDI-related partner ERp57 5. which is disulfide-linked to tapasin6. This allows assembly and folding of Class I molecules, providing a groove for insertion of a peptide 7. fed in from the cytosol by the TAP transporter that is recruited by tapasin 8. The peptides are derived from proteosomal degradation.