The major histocompatibility complex(MHC)of proteins that exists in all vertebrates is encoded by a cluster of genes associated with the immune response and related functions.MHC is divided into MHC I,II,and III;MHC I is involved in antigenic presentation,binding T cell receptors,and leading ultimately to specific cellular immune responses.The complicated functions of MHC I are determined by the nature of the complex.The crystal structure of MHC I has been solved for many animals,revealing the relationship between spatial structure and function.MHC I consists of an a heavy chain and a b2m light chain,both ligated non-covalently to a complex when a peptide is bound to the antigenic-binding groove.The a heavy chain is divided into an extracellular domain,a transmembrane domain,and an intracellular domain.The extracellular domain consists of sub-regions a1,a2,and a3.The a1 and a2 together form the antigenic-binding groove and bind antigenic peptides with 8–10 amino acid residues.MHC I can form a stable spatial structure;however,it should be noted that there are differences in the structure of MHC I among animal species,including anchored amino acids in binding peptides,binding sites,molecular distance,crystallization conditions,etc.Here,progress in determination of the crystal structure of human,mouse,chicken,non-human primate,and swine MHC I is described in detail.
