A glycan-phosphatidylinositol-specific phospholipase D in human serum.
A group of proteins anchored to the cell by phosphatidylinositol (PI) has recently been identified. The significance of this new class of membrane anchor is unknown; one possibility is that it facilitates release of the molecule by phospholipases. In fact, phospholipase C enzymes specific for the complex carboxyl-terminal glycolipids of these proteins have been isolated from African trypanosomes and from hepatocyte plasma membranes. This study reports the discovery of a glycan-PI-specific phospholipase D in human serum that cleaves both the membrane form of the variant surface glycoprotein of African trypanosomes and its glycolipid precursor, but not phosphatidylethanolamine, phosphatidylcholine, or phosphatidylinositol. Decay-accelerating factor, another PI-anchored molecule, is also cleaved by the enzyme and converted from a hydrophobic to a soluble protein. The enzyme is Ca2+-dependent, heat labile, and not affected by the inhibitor of serine proteases, phenylmethylsulfonylfluoride. Its function is not known, but the present findings indicate that it participates in the metabolism of glycolipid-anchored membrane proteins.
D018958:CD55 Antigens; D006017:Glycolipids / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010739:Phospholipase D / Q000037:antagonists & inhibitors / Q000097:blood*; D010740:Phospholipases / Q000097:blood*; D012995:Solubility; D013379:Substrate Specificity; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000378:metabolism
D018958:CD55 Antigens; D006017:Glycolipids; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D014643:Variant Surface Glycoproteins, Trypanosoma; D010740:Phospholipases; D010739:Phospholipase D