engleski

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 complex 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 manosylating several consecutive serine and threonine resiudues. In addition, it is shown that O-mannosylation by Pmt4 prevents N-glycosylation by blocking the hidroxy amino acid of the single N-glycosylation site present in Ccw5. These data prove that the O- and N-glycosylation machineries complete for Ccw5 ; therefore O-mannosylation by Pmt4 precedes N-glycosylation.

Protein glycosylation; Yeast cell wall; Cell wall mannoproteins

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