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Variant surface glycoproteins (VSG) are a type of proteins coating the surface of some infectious microorganisms (e.g. ''Trypanosoma brucei'') and helping them to evade the host's immune system by mean of antigenic variation. The VSG protein is a key molecule for immune escape and parasitic success. Combinatorial processes increase the diversity of variable surface glycoproteins. The parasite is expressing a series of antigenically distinct VSGs from more than 2000 complete and partial (pseudogenes) VSG genes. The genes are located in telomeric and subtelomeric regions and are often activated by the duplicative transposition of a silent basic copy gene into an unlinked telomerically located expression site, producing an active expression-linked copy of that gene. == In ''Trypanosoma brucei'' == In ''Trypanosoma brucei'' (see Trypanosoma_brucei#VSG_coat), the variant surface glycoprotein is a major surface antigen. The cell surface of the bloodstream form features a dense coat of variable surface glycoproteins which is replaced by an equally dense coat of procyclins when the parasite differentiates into the procylic form in the tsetse fly midgut. There is a very fast inhibition of VSG gene transcription which occurs as soon as the temperature is lowered. The VSGs from ''T. brucei'' are attached to the plasma membrane via a glycosyl-phosphatidylinositol (GPI) anchor. The coat is composed of VSG dimers and forms a macromolecular diffusion barrier. Glycoproteins vary in primary amino acid sequence, the number of N-glycosylation sites, and the types of N-linked oligosaccharides and glycosylphosphatidylinositol membrane anchors they contain. VSG MITat.1.5 is glycosylated at all three potential N-glycosylation sites. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「variable surface glycoprotein」の詳細全文を読む スポンサード リンク
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