Two Naturally Occurring α2,6-Sialyltransferase Forms with a Single Amino Acid Change in the Catalytic Domain Differ in Their Catalytic Activity and Proteolytic Processing

摘要: The alpha2,6-sialyltransferase (ST) is a Golgi glycosyltransferase that adds sialic acid residues to glycoprotein N-linked oligosaccharides. Here we show two forms of are expressed by the liver and encoded different RNAs differ single nucleotide. ST tyr possesses Tyr at amino 123, whereas cys Cys this position. more catalytically active than cys; however, both functional when introduced into tissue culture cells. proteolytic processing turnover proteins dramatically. retained intact in COS-1 cells, rapidly cleaved secreted. Analysis oligosaccharides these demonstrates enter late Golgi. However, differences may be related their localization, because but not low levels on cell surface. possibility post-Golgi compartment supported observation 20 degrees C temperature block, which stops protein transport trans network, blocks cleavage secretion tyr.