CLIP (protein)

CLIP (protein)

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CLIP binding to MHC class II molecules.

The Class II-associated invariant chain peptide (CLIP) is a small peptide that plays a crucial role in the immune system, particularly in the antigen presentation process. CLIP is derived from the invariant chain (Ii), a protein that associates with MHC class II molecules during their synthesis in the endoplasmic reticulum.

Function

CLIP functions as a placeholder peptide that occupies the peptide-binding groove of MHC class II molecules. This prevents premature binding of endogenous peptides to MHC class II molecules while they are in the endoplasmic reticulum. The invariant chain, from which CLIP is derived, also assists in the proper folding and transport of MHC class II molecules to the endosomal/lysosomal compartments.

Mechanism

Once the MHC class II molecules reach the endosomal/lysosomal compartments, the invariant chain is degraded by proteases, leaving CLIP bound to the MHC class II molecule. The removal of CLIP is facilitated by the HLA-DM molecule, which catalyzes the exchange of CLIP for antigenic peptides. This peptide exchange is crucial for the presentation of foreign antigens to CD4+ T cells, a key step in the activation of the adaptive immune response.

Clinical Significance

The proper functioning of CLIP and its interaction with MHC class II molecules is essential for immune surveillance and the prevention of autoimmune diseases. Defects in this process can lead to impaired antigen presentation and contribute to the development of autoimmune disorders.

Related pages

• Major Histocompatibility Complex
• Antigen presentation
• Invariant chain
• HLA-DM
• CD4+ T cell