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Glycobiology, 2002, Vol. 12, No. 11 30G-33G
© 2002 Oxford University Press

GLYCO-FORUM SECTION

Letter to the Glyco-Forum

Hypoglycosylation in the alg12{Delta} yeast mutant destabilizes protease A and causes proteolytic loss of external invertase

John F. Cipollo1,3 and Robert B. Trimble2,3,4

3 Department of Biomedical Sciences, State University of New York at Albany School of Public Health, Albany, NY 12201, USA and 4 Wadsworth Center, New York State Department of Health, P.O. Box 509, Albany, NY 12201, USA

Abstract

The Saccharomyces cerevisiae alg12{Delta} mutant accumulates oligosaccharide lipid with a Man7GlcNAc2 oligosaccharide. To determine the N-glycan structures present on S. cerevisiae glycoproteins in the alg12{Delta} strain, we made attempts to purify external invertase, a highly glycosylated secreted protein. These efforts revealed that, in the alg12{Delta} background, external invertase was mildly hypoglycosylated and rapidly destroyed proteolytically. Although secreted alg9{Delta} invertase was more severely hypoglycosylated than the alg12{Delta} form, it was paradoxically stable during purification. The loss of periplasmic invertase was prevented by addition of pepstatin A to the cell cultures, suggesting that aspartyl proteases were active. We found that during overexpression of invertase in alg12{Delta} yeast, sufficient protease A was mistargeted to the periplasmic space, where it hydrolyzed the invertase. Even though alg9{Delta} invertase is underglycosylated in comparison to the alg12{Delta} form, it is more stable because in this genetic background much less protease A is secreted compared to alg12{Delta} cells. These observations may be relevant to studies using other extracellular proteins (e.g., mating factors, {alpha}-glucosidase) as probes when characterizing glycosylation defects in yeast.

Footnotes

1 Present address: Boston University Goldman School of Dental Medicine, Boston, MA 02118–2392, USA

2 To whom correspondence should be addressed; E-mail: trimble@wadsworth.org


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