The functional role of protein O-mannosylation
Final Report Abstract
Protein O-mannosylation represents a vital post-translational modification that is initiated in the endoplasmic reticulum (ER). In baker´s and fission yeast, the lack of O-mannosylation results in cell death. Phenotypes of conditional viable O-mannosylation mutants indicated that O-mannosylation affects cell wall integrity and cell morphogenesis. However, at the beginning of this project, the molecular basis of these defects was only very poorly defined. Transcriptome analyses showed that defective O-mannosylation predominantly affects ER stress- and cell wall-associated processes. Many cell wall proteins are highly O-mannosylated. Our data indicate that decreased O-mannosylation results in misprocessed cell wall proteins thereby probably inducing ER stress. Consequently, cell wall integrity pathways are activated to buffer the cell against defects in cell wall biosynthesis. Our transcriptome study further identified a new compensatory response between O-mannosylation and N-glycosylation, particularly the formation of high mannose outer chains. Identification of the Schizosaccharomyces pombe mannose polymerase II subunit Mnn10p, which is involved in the extension in N-linked outer chains, as a multicopy suppressor (MCS) of attenuated levels of O-mannosylation further substantiates this finding. Analyses of S. pombe O-mannosylation mutants revealed that defective O-mannosylation significantly affects formation of the septum, especially the balanced levels of cell wall glucans. The identification of the MCS Sup11 gave an explanation for this defect. We could demonstrate that Sup11 is highly O-mannosylated and that a lack of O-mannosylation significantly affected Sup11p stability and/or maturation. We showed further that Sup11+ is an essential gene that is indispensable for ß-1,6-glucan biosynthesis. This lack of ß-1,6-glucan interferes with ß-1,3-glucan homeostasis, thereby causing lethality.
Publications
- (2009) Der Einfluss der Glykosylierung auf Zellwandintegrität und weitere vitale Prozesse in den Modellorganismen Schizosaccharomyces pombe und Saccharomyces cerevisiae. Dissertation, Combined Faculties for the Natural Sciences and for Mathematics, University of Heidelberg
Hutzler
- (2009) Protein O-mannosylation: conserved from bacteria to humans. Glycobiology 19:816-28
Lommel M, Strahl S
- (2011) Functional and genomic analyses of blocked protein O- mannosylation in baker's yeast. Mol Microbiol. 79:1529-46
Arroyo J, Hutzler J, Bermejo C, Ragni E, García-Cantalejo J, Botías P, Piberger H, Schott A, Sanz AB, Strahl S
