Pmt-mediated O mannosylation stabilizes an essential component of the secretory apparatus, Sec20p, in Candida albicans.

Sec20p is an essential endoplasmic reticulum (ER) membrane protein in yeasts, functioning as a tSNARE component in retrograde vesicle traffic. We show that Sec20p in the human fungal pathogen Candida albicans is extensively O mannosylated by protein mannosyltransferases (Pmt proteins). Surprisingly, Sec20p occurs at wild-type levels in a pmt6 mutant but at very low levels in pmt1 and pmt4 mutants and also after replacement of specific Ser/Thr residues in the lumenal domain of Sec20p. Pulse-chase experiments revealed rapid degradation of unmodified Sec20p (38.6 kDa) following its biosynthesis, while the stable O-glycosylated form (50 kDa) was not formed in a pmt1 mutant. These results suggest a novel function of O mannosylation in eukaryotes, in that modification by specific Pmt proteins will prevent degradation of ER-resident membrane proteins via ER-associated degradation or a proteasome-independent pathway.

Citation

Yvonne Weber, Stephan K-H Prill, Joachim F Ernst. Pmt-mediated O mannosylation stabilizes an essential component of the secretory apparatus, Sec20p, in Candida albicans. Eukaryotic cell. 2004 Oct;3(5):1164-8

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PMID: 15470244

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