NATURAL SELECTION ON THE PEPTIDE-BINDING REGIONS OF MAJOR HISTOCOMPATIBILITY COMPLEX MOLECULES

摘要: The major histocompatibility complex (MHC) of vertebrates is a multigene family whose products encode cell surface glycoproteins that function to present peptides T cells (Klein 1986). There are two subfamilies, class I and II, the members which differ both structurally functionally. Class molecules have nearly universal pattern expression cytotoxic cells, while II expressed on antigen-presenting immune system. In mammals, loci linked together in single gene complex, also includes some genes neither an evolutionary nor functional relationship MHC genes, others which, although not evolutionarily related play roles peptide presentation. Both heterodimers with four extracellular domains, but they achieve analogous structures different ways. [ heterodimer ct chain consisting three domains (cq, a~, ct3), transmembrane portion, cytoplasmic domain. o~3 domain associates noncovalently ~2-microglobulin ([32m). ~32m encoded outside shows evidence t~3 domain, like it C ltype belonging immunoglobulin (Ig) superfamily (Williams Barclay 1988). consists o~ ~3 chain, each (~1 c~2 131 ~3% respectively), region, tail; chains by within complex. Like membrane-proximal