Functions forMHC class I carbohydrates inside and outside the cell

Major histocompatibility complex (MHC) class I heavy chain glycoproteins have an invariant N-linked glycosylation site at Asn86, which is found between two extremely variable protein domains. For human MHC class I molecules, Asn is the only site of glycosylation and the attached oligosaccharides are remarkably uniform. The carbohydrate initiates interactions with calnexin in the endoplasmic reticulum that facilitate the assembly of MHC class I molecules and their delivery to the cell surface. However, recognition of MHC class I molecules by antibodies and T cells is indifferent to the carbohydrate, although lines of circumstantial evidence implicate lectins and carbohydrates in the recognition of MHC class I glycoproteins by natural killer cells.