O-mannosylation precedes and potentially controls the N-glycosylation of a yeast cell wall glycoprotein.
Secretory proteins in yeast are N- and O-glycosylated while they enter the endoplasmic reticulum. N-glycosylation is initiated by the oligosaccharyl transferase complex and O-mannosylation is initiated by distinct O-mannosyltransferase complexes of the protein mannosyl transferase Pmt1/Pmt2 and Pmt4 families. Using covalently linked cell-wall protein 5 (Ccw5) as a model, we show that the Pmt4 and Pmt1/Pmt2 mannosyltransferases glycosylate different domains of the Ccw5 protein, thereby mannosylating several consecutive serine and threonine residues. In addition, it is shown that O-mannosylation by Pmt4 prevents N-glycosylation by blocking the hydroxy amino acid of the single N-glycosylation site present in Ccw5. These data prove that the O- and N-glycosylation machineries compete for Ccw5; therefore O-mannosylation by Pmt4 precedes N-glycosylation.
Ecker
Margit
M
Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, 93040 Regensburg, Germany.
Mrsa
Vladimir
V
Hagen
Ilja
I
Deutzmann
Rainer
R
Strahl
Sabine
S
Tanner
Widmar
W
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002473:Cell Wall / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D008358:Mannose / Q000737:chemistry*; D008364:Mannosyltransferases / Q000737:chemistry*; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000502:physiology; D017386:Sequence Homology, Amino Acid
C482291:CIS3 protein, S cerevisiae; D005656:Fungal Proteins; D006023:Glycoproteins; D029701:Saccharomyces cerevisiae Proteins; D008364:Mannosyltransferases; D008358:Mannose