CLASS I MOLECULES - on the bottom and two alpha helices on...

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CLASS I MOLECULES Class I molecules are composed of two polypeptide chains; one encoded by the BCA region and another (ß2-microglobulin) that is encoded elsewhere. The MHC-encoded polypeptide is about 350 amino acids long and glycosylated, giving a total molecular weight of about 45 kDa. This polypeptide folds into three separate domains called alpha-1, alpha-2 and alpha-3. ß2- microglobulin is a 12 kDa polypeptide that is non-covalently associated with the alpha-3 domain . Between the alpha-1 and alpha-2 domains lies a region bounded by a beta-pleated sheet
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Unformatted text preview: on the bottom and two alpha helices on the sides. This region is capable of binding (via non-covalent interactions) a small peptide of about 10 amino acids. This small peptide is "presented" to a T-cell and defines the antigen "epitope" that the T-cell recognizes (see below). The following images illustrate the structure of the class I MHC as seen schematically, and three dimensionally from the side and from the top (T-cell perspective). The MHC-encoded polypeptide is shown in blue, the 2-microglobulin is green and the peptide antigen is red....
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