title: Membrane association is a determinant for substrate recognition by PMT4 protein O-mannosyltransferases.
abstract: Protein O-mannosylation represents an evolutionarily conserved, essential posttranslational modification with immense impact on a variety of cellular processes. In humans, O-mannosylation defects result in Walker-Warburg syndrome, a severe recessive congenital muscular dystrophy associated with defects in neuronal migration that produce complex brain and eye abnormalities. In mouse and yeasts, loss of O-mannosylation causes lethality. Protein O-mannosyltransferases (PMTs) initiate the assembly of O-mannosyl glycans. The evolutionarily conserved PMT family is classified into PMT1, PMT2, and PMT4 subfamilies, which mannosylate distinct target proteins. In contrast to other types of glycosylation, signal sequences for O-mannosylation have not been identified to date. In the present study, we identified signals that determine PMT4-dependent O-mannosylation. Using specific model proteins, we demonstrate that in yeast Pmt4p mediates O-mannosylation of Ser/Thr-rich membrane-attached proteins. The nature of the membrane-anchoring sequence is nonrelevant, as long as it is flanked by a Ser/Thr-rich domain facing the endoplasmic reticulum lumen. Our work shows that, in contrast to several other types of glycosylation, PMT4 O-mannosylation signals are not just linear protein's primary structure sequences but rather are highly complex. Based on these findings, we performed in silico analyses of the Saccharomyces cerevisiae proteome and identified previously undescribed Pmt4p substrates. This tool for proteome-wide identification of O-mannosylated proteins is of general interest because several of these proteins are major players of a wide variety of cellular processes.
authors.affiliation: Department of Cell Chemistry, Institute of Plant Sciences, University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Hutzler
authors.forename: Maria
authors.initials: M
authors.lastname: Schmid
authors.forename: Thomas
authors.initials: T
authors.lastname: Bernard
authors.forename: Bernard
authors.initials: B
authors.lastname: Henrissat
authors.forename: Sabine
authors.initials: S
authors.lastname: Strahl
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D002462:Cell Membrane / Q000201:enzymology*; D006031:Glycosylation; D017261:Glycosylphosphatidylinositols / Q000502:physiology; D008358:Mannose / Q000378:metabolism; D008364:Mannosyltransferases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data
chemical_list: D017261:Glycosylphosphatidylinositols; D008364:Mannosyltransferases; C082696:protein O-mannosyltransferase; D008358:Mannose