Preferential transfer of the complete glycan is determined by the oligosaccharyltransferase complex and not by the catalytic subunit.
Most eukaryotic cells show a strong preference for the transfer in vivo and in vitro of the largest dolichol-P-P-linked glycan (Glc(3)Man(9)GlcNAc(2)) to protein chains over that of biosynthetic intermediates that lack the full complement of glucose units. The oligosaccharyltransferase (OST) is a multimeric complex containing eight different proteins, one of which (Stt3p) is the catalytic subunit. Trypanosomatid protozoa lack an OST complex and express only this last protein. Contrary to the OST complex from most eukaryotic cells, the Stt3p subunit of these parasites transfers in cell-free assays glycans with Man(7-9)GlcNAc(2) and Glc(1-3)Man(9)GlcNAc(2) compositions at the same rate. We have replaced Saccharomyces cerevisiae Stt3p by the Trypanosoma cruzi homologue and found that the complex that is formed preferentially transfers the complete glycan both in vivo and in vitro. Thus, preference for Glc(3)Man(9)GlcNAc(2) is a feature that is determined by the complex and not by the catalytic subunit.
Castro
Olga
O
Laboratory of Glycobiology, Fundación Instituto Leloir, Avenida Patricias Argentinas, 435 C1405 BWE Buenos Aires, Argentina.
Movsichoff
Federico
F
Parodi
Armando J
AJ
D000818:Animals; D020134:Catalytic Domain; D043402:Cathepsin A / Q000378:metabolism; D002474:Cell-Free System; D006031:Glycosylation; D006602:Hexosyltransferases / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014349:Trypanosoma cruzi / Q000201:enzymology*
D008565:Membrane Proteins; D011134:Polysaccharides; D015800:Protozoan Proteins; D029701:Saccharomyces cerevisiae Proteins; D006602:Hexosyltransferases; C096554:STT3 protein, S cerevisiae; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase; D043402:Cathepsin A