Characterization of O-mannosyltransferase family in Schizosaccharomyces pombe

Abstract Protein O -glycosylation is an essential protein modification in eukaryotic cells. In Saccharomyces cerevisiae , O -mannosylation is initiated in the lumen of the endoplasmic reticulum by O -mannosyltransferase gene products (Pmt1p–7p). A search of the Schizosaccharomyces pombe genome database revealed a total of three O -glycoside mannosyltransferase homologs ( ogm1 + , ogm2 + , and ogm4 + ), closely related to Saccharomyces cerevisiae PMT1 , PMT2 , and PMT4 . Although individual ogm genes were not found to be essential, ogm1 Δ and ogm4 Δ mutants exhibited aberrant morphology and failed to agglutinate during mating. The phenotypes of the ogm4 Δ mutant were not complemented by overexpression of ogm1 + or ogm2 + , suggesting that each of the Ogm proteins does not have overlapping functions. Heterologous expression of a chitinase from S. cerevisiae in the ogm mutants revealed that O -glycosylation of chitinase had decreased in ogm1 Δ cells. A GFP-tagged Fus1p from S. cerevisiae was specifically not glycosylated and accumulated in the Golgi in ogm4 Δ cells. These results indicate that O -glycosylation initiated by Ogm proteins plays crucial physiological roles and can serve as a sorting determinant for protein transport of membrane glycoproteins in S. pombe .