Which is the correct order of activities showcased by endogenous antigens? i) Peptide binding to MHC Class I ii) Transport to Endoplasmic Reticulum iii) Generation of Peptide from proteolysis

Which is the correct order of activities showcased by endogenous antigens? i) Peptide binding to MHC Class I ii) Transport to Endoplasmic Reticulum iii) Generation of Peptide from proteolysis Correct Answer iii—ii—i

Processing of endogenous antigens involve major 3 activities. In the first activity, peptides are generated. This takes place via proteolysis as proteins are targeted in order to combine with ubiquitin. Once the ubiquitin-protein complex is formed, it gets degraded by proteosome. These proteosomes generate the required peptides which can further bind to MHC class I. The second step involves transport of these peptides into the endoplasmic reticulum via TAP proteins. The third and final step involves binding of peptide to MHC class I mediated by tapasin and calreticulin.