Isolation of new nonconditional Saccharomyces cerevisiae mutants defective in asparagine-linked glycosylation

Abstract

We describe the isolation and partial characterization of Saccharomyces cerevisiae nonconditional mutants that show defects in N-glycosylation of proteins. The selection method is based on the reduction of affinity for the ion exchanger QAE-Sephadex as a consequence of the decrease in the negative charge of the cell surface. This characteristic reflects a decrease in the incorporation of mannosylphosphate units into the N-linked oligosaccharides of the mannoproteins. The mutants exhibit low affinity for the basic dye alcian blue and for that reason we have called them Idb (low dye binding) mutants. Eight of the complementation groups seem to be new as shown by complementation studies with previously isolated mutants of similar phenotype. Four of the groups showed a significant reduction in the number and/or size of the N-linked oligosaccharides attached to secreted invertase. We have analyzed the N-linked oligosaccharides of Idb1 and Idb2, the mutants that show the most drastic reduction in the affinity for the alcian blue dye. In both cases, the purified endo H-released oligosaccharides from the mannoproteins lacked detectable amounts of phosphate groups as shown by ion exchange chromatography and the 1H NMR spectra. In addition, Ibd1 synthesizes a truncated and unbranched outer chain lacking any alpha (1,2) linked mannoses attached to the alpha (1,6) linear backbone.

MNN5 Encodes an Iron-Regulated α-1,2-Mannosyltransferase Important for Protein Glycosylation, Cell Wall Integrity, Morphogenesis, and Virulence in Candida albicans

“…Since CaMnn5 shares high sequence homology with two S. cerevisiae mannosyltransferases, Mnn5 and Mnn2, we wanted to know whether CaMNN5 can functionally complement an S. cerevisiae mnn2⌬ or mnn5⌬ mutant. Negatively charged mannophosphate units are known to be incorporated into N-linked oligosaccharides of mannoproteins, and thus defects in N-glycosylation are often associated with a decrease in the cell's affinity for the cationic dye Alcian blue (31,34). Both mnn2⌬ and mnn5⌬ mutant strains showed a significant loss of Alcian blue binding ( Fig.…”

Genome-wide expression profile of the mnn2Δ mutant of Saccharomyces cerevisiae

“…We have isolated and characterized several low dye binding (ldb) mutants obtained by random mutagenesis experiments (Man˜as et al 1997(Man˜as et al , 1998Olivero et al 2003;Corbacho et al 2004) and we have also performed a genome-wide screen that allowed us to identify 199 non-essential genes whose deletion resulted in a detectable ldb phenotype (Corbacho et al 2005). We have studied as well the behaviour of some previously isolated mnn mutants related to mannosyl phosphorylation.…”

“…This finding is in contrast to the behaviour of previously isolated mutants with severe reduction in the incorporation of mannosyl phosphate groups, such as mnn4, mnn6, ldb1 and ldb2. None of these strains showed detectable differences in the inhibition of mannosyl phosphate transfer to the two possible acceptor sites in the core (Herna´ndez et al 1989;Man˜as et al 1997). These results pointed towards a link between the function of MNN2 and that of other genes involved in building the N-linked chains of the mannoproteins, in particular, in mannosyl phosphate transfer.…”

A genome-wide screen for Saccharomyces cerevisiae nonessential genes involved in mannosyl phosphate transfer to mannoprotein-linked oligosaccharides

“…Although the function of such groups remains to be established, their location in the outer layer of the cell wall makes them potential ligands to interact with the cells of the host. The availability of the complete collection of deletion strains in S. cerevisiae and of methods to detect defects in mannosyl phosphorylation (Ballou, 1990;Mañas et al, 1997) makes this organism a better model for the study of the process. The phenotype analysis of this collection allows investigation of the potential role of every nonessential gene in the transfer of mannosyl phosphate.…”