Proteolytic processing of a secreted glycoprotein and O-glycosylation of mannoproteins are affected in the N-glycosylation mutant Saccharomyces cerevisiae ldb1.
In a previous work [P.I. Mañas, I. Olivero, M. Avalos, L.M. Hernández, Glycobiology, 7 (1997) 487-497], we described the isolation and characterization of the Saccharomyces cerevisiae ldb1 mutant which is affected in several steps of the N-glycosylation of mannoproteins probably due to a malfunction of the Golgi apparatus. Here, we found that two further functions assigned to the Golgi cisternae are also affected in the mutant: proteolytic processing of a secreted protein and O-glycosylation. We found that around 70% of the exoglucanase activity that is secreted into the culture medium by ldb1 bears an extra tetrapeptide in its NH2-terminus due to incomplete proteolytic processing. The O-linked oligosaccharides from ldb1 mnn1 were indistinguishable from those synthesized by the parental strain mnn1. However, when the O-oligosaccharides from the wild type and ldb1 were compared, we found a significant decrease in the tetrasaccharide in the latter, as well as a concomitant increase in the disaccharide, suggesting a defect in the Kre2p/Mnt1p involved in the transfer of the third mannose of these residues.
Mañas
P
P
Department of Microbiology, University of Extremadura, 06071 Badajoz, Spain.
Olivero
I
I
Hernández
L M
LM
D002236:Carbohydrate Conformation; D043326:Glucan 1,3-beta-Glucosidase; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism*; D006031:Glycosylation; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D009844:Oligosaccharides / Q000032:analysis / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D001617:beta-Glucosidase / Q000235:genetics / Q000378:metabolism
D006023:Glycoproteins; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; C025363:mannoproteins; D001617:beta-Glucosidase; D043326:Glucan 1,3-beta-Glucosidase