MHC class II protein binding

Definition

Target type: molecularfunction

Binding to a major histocompatibility complex class II molecule; a set of molecules displayed on cell surfaces that are responsible for lymphocyte recognition and antigen presentation. [GOC:jl]

MHC class II proteins are integral membrane glycoproteins that play a critical role in the adaptive immune response by presenting processed antigens to CD4+ T lymphocytes. Their molecular function involves a complex series of steps that ultimately enable the recognition of foreign peptides by T cells, leading to the activation of immune responses.

1. **Antigen Processing:**
- MHC class II molecules are synthesized in the endoplasmic reticulum (ER) and associate with a chaperone protein called invariant chain (Ii).
- Ii prevents the premature binding of peptides to MHC class II molecules in the ER.
- The MHC class II-Ii complex travels to the endosomal compartment where it encounters antigens.
- Ii is degraded, leaving a small fragment called CLIP (class II-associated invariant chain peptide) bound to the peptide binding groove of MHC class II.
- The CLIP is then exchanged for exogenous peptides that are derived from degraded proteins taken up by antigen-presenting cells (APCs).

2. **Peptide Binding:**
- The peptide binding groove of MHC class II molecules is a shallow, open cleft that can accommodate peptides of varying lengths and sequences.
- The groove is lined with polymorphic residues, which contribute to the diversity of MHC class II molecules and their ability to bind a wide range of peptides.
- Peptide binding is a highly specific process, and MHC class II molecules typically bind peptides that have a particular anchor residue motif.
- Anchor residues are amino acids in the peptide that interact with specific pockets in the peptide binding groove.

3. **T Cell Recognition:**
- Once an MHC class II molecule has bound a peptide, it is transported to the cell surface and presented to CD4+ T lymphocytes.
- CD4+ T cells express the T cell receptor (TCR), which can recognize the peptide-MHC class II complex.
- The TCR binds to the MHC class II molecule and the bound peptide, initiating a signaling cascade within the T cell.

4. **T Cell Activation and Immune Response:**
- The activation of CD4+ T cells leads to the production of cytokines, which can promote the differentiation of other immune cells, such as cytotoxic T lymphocytes (CTLs), and the activation of the adaptive immune response.
- The activated T cells can also differentiate into memory cells, providing long-lasting immunity against specific pathogens.

In summary, the molecular function of MHC class II protein binding involves antigen processing, peptide binding, T cell recognition, and ultimately the activation of the adaptive immune response. This process is essential for the recognition and elimination of foreign pathogens, and plays a critical role in maintaining immune homeostasis.'
"

Proteins (2)

Compounds (3)