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

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CLASS II MOLECULES Class II molecules are composed of two polypeptide chains, both encoded by the D region. These polypeptides (alpha and beta) are about 230 and 240 amino acids long, respectively, and are glycosylated, giving molecular weights of about 33 kDa and 28 kDa. These polypeptides fold into two separate domains; alpha-1 and alpha-2 for the alpha polypeptide, and beta-1 and beta-2 for the beta polypeptide. Between the alpha-1 and beta-1 domains lies a region very similar to that seen on the class I molecule. This region, bounded by a beta-pleated sheet on the
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Unformatted text preview: bottom and two alpha helices on the sides, 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 II MHC as seen schematically, and three dimensionally from the side and from the top (T-cell perspective). The MHC-encoded polypeptides are shown in yellow and green, while the peptide antigen is shown in red....
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