Question

What is the role of the invariant chain?

A. To prevent peptide binding to class II in the ER
B. To assist in folding class II a and B chains
C. To direct class II to the endocytic compartment
D. To serve as a substrate for proteases in the lysosome
E. all of the above

Answer 1

The invariant chain directs class II MHC molecules to the endocytic compartment, prevents peptide binding in the ER, and gets degraded in the lysosome.

Step-by-step explanation:

The role of the invariant chain, also known as Ii or CD74, is to direct class II major histocompatibility complex (MHC) molecules to the endocytic compartment.

Ii prevents peptide binding to class II MHC molecules in the endoplasmic reticulum (ER) by covering the peptide-binding groove.

Once in the endocytic compartment, the invariant chain is degraded by proteases in the lysosome, leaving behind a small fragment known as CLIP. CLIP then gets replaced by antigenic peptides, allowing the class II MHC molecule to present these peptides to immune cells.