Which poion of MHC 1 complex forms the component of antigen presenting pa:

Ans. (b) Distal pa of alpha chain Ref. Ananthanarayan 8/e, p 133, 9/e p 139 MHC I/ HLA I - Class 1 molecule consists of a three domains of heavy alpha peptide chain (al; a2; a3) which are non-covalently linked to smaller B2 microglobulin peptide. - The distal domain (alpha 1 and alpha 2) of MHC 1 have highly variable amino acid sequences and are folded to form a cavity or groove. Protein antigens are bound to this groove for presentation to CD8 T cells. MHC II/ HLA II - MHC II antigens are heterodimer consisting of an alpha and beta chain. Each chain has two domain proximal one is constant and distal one is variable. - The two distal domain (alpha 1 , beta 1) constitute the antigen binding site, for recognition by CD4 T cells. - Both class 1 and class 2 are members of immunoglobu I in gene super family. MHC III / HLA III - MHC III are heterogenous they include complement components involved in the formation of C3 convease, heat shock protein and tumor necrosis factor.