MHC class I Structure and Function

These are glycoproteins found on all nucleated cells. These proteins are coded by three genes HLA-A, HLA-B and HLA-C present on the short arm of chromosome 6. MHC class I proteins interacts primarily with cytotoxic T cells.

Structure:

Look at the figure first

MHC Class I

The protein is a cell surface protein and a heterodimer consisting of a long α chain (α-subunit) and a short β chain (β subunit) joined by non-covalent interactions.

β-chain is called as β2-microglobulin. Remember, β2-microglobulin is encoded on chromosome 15, unlike α chain on chromosome 6.

Similar to immunoglobulins, α chain has 4 regions, constant C terminal regions and hyper variable N-terminal regions. α chain has a

a) Cytoplasmic carboxyl region

b) A transmembrane region

c) A higly conserved α-3 region

d) A highly polymorphic or hypervariable peptide binding N terminal region made of α-1 and α-2 regions.

β2-microglobulin is associated with α chain that helps in maintaining proper confirmation of molecule.

Functions of MHC class I proteins:

• Helps immune system in recognising self-cells from non-self cells.
• Interacts with cytotoxic T cells leading to degradation of antigen
• Responsible for rejection of transplanted organs.