The Ktr1p, Ktr3p, and Kre2p/Mnt1p mannosyltransferases participate in the elaboration of yeast O- and N-linked carbohydrate chains.
We have determined a role for Ktr1p and Ktr3p as mannosyltransferases in the synthesis of the carbohydrate chains attached to Saccharomyces cerevisiae O- and N-modified proteins. KTR1 and KTR3 encode related proteins that are highly similar to the Kre2p/Mnt1p Golgi alpha1,2-mannosyltransferase (Lussier, M., Camirand, A., Sdicu, A.-M., and Bussey, H. (1993) Yeast 9, 1057-1063; Mallet, L., Bussereau, F., and Jacquet, M. (1994) Yeast 10, 819-831). Examination of the electrophoretic mobility of a specifically O-linked protein from mutants and an analysis of their total O-linked mannosyl chains demonstrates that Ktr1p, Ktr3p, and Kre2p/Mnt1p have overlapping roles and collectively add most of the second and the third alpha1,2-linked mannose residues on O-linked oligosaccharides. Determination of the mobility of the specifically N-linked glycoprotein invertase in different null strains indicates that Ktr1p, Ktr3p, and Kre2p are also jointly involved in N-linked glycosylation, possibly in establishing some of the outer chain alpha1,2-linkages.
Lussier
M
M
Department of Biology, McGill University, Montréal, Québec, Canada, H3A 1B1.
Sdicu
A M
AM
Bussereau
F
F
Jacquet
M
M
Bussey
H
H
D006031:Glycosylation; D008364:Mannosyltransferases / Q000378:metabolism*; D009844:Oligosaccharides / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism*
D009844:Oligosaccharides; D008364:Mannosyltransferases