Abstract
In a wide range of organisms, dolichyl phosphate mannose (DPM) synthase is a complex of tree proteins Dpm1, Dpm2, and Dpm3. However, in the yeast Saccharomyces cerevisiae, it is believed to be a single Dpm1 protein. The function of Dpm3 is performed in S. cerevisiae by the C-terminal transmembrane domain of the catalytic subunit Dpm1. Until present, the regulatory Dpm2 protein has not been found in S. cerevisiae. In this study, we show that, in fact, the Yil102c-A protein interacts directly with Dpm1 in S. cerevisiae and influences its DPM synthase activity. Deletion of the YIL102c-A gene is lethal, and this phenotype is reversed by the dpm2 gene from Trichoderma reesei. Functional analysis of Yil102c-A revealed that it also interacts with glucosylphosphatidylinositol-N-acetylglucosaminyl transferase (GPI-GnT), similar to DPM2 in human cells. Taken together, these results show that Yil102c-A is a functional homolog of DPMII from T. reesei and DPM2 from humans.
Highlights
Dolichyl phosphate mannose (DPM) is the donor of four mannosyl residues in the oligosaccharide precursor formed on dolichyl phosphate (DolP) during protein N-glycosylation of the first mannose in O-mannosylation, of all three mannoses in glycosyl phosphatidyl inositols (GPIs) [1,2,3,4,5,6], and of the mannose in C-mannosylation [7].The synthesis of dolichyl phosphate mannose (DPM) is catalyzed by the DPM synthase, which transfers the mannosyl residue from (Guanosine Diphosphate –mannose) GDP-mannose to DolP
Maeda et al [14] reported that the DPM synthase from humans forms a complex of three subunits, DPM1, DPM2 and DPM3, where DPM1 is the catalytic subunit, DPM2 regulates its activity, and DPM3 anchors the complex in the ER membrane
The DPMII protein is a regulatory subunit of DPM synthase in Trichoderma, while in S. cerevisiae, the DPM synthase was reported to be a single fully functional Dpm1 protein [8,12,23] regulated by the DPM synthase was reported to be a single fully functional Dpm1 protein [8,12,23] regulated by phosphorylation/dephosphorylation of serine 141 by cAMP-dependent protein kinase [24]
Summary
Dolichyl phosphate mannose (DPM) is the donor of four mannosyl residues in the oligosaccharide precursor formed on dolichyl phosphate (DolP) during protein N-glycosylation of the first mannose in O-mannosylation, of all three mannoses in glycosyl phosphatidyl inositols (GPIs) [1,2,3,4,5,6], and of the mannose in C-mannosylation [7].The synthesis of DPM is catalyzed by the DPM synthase, which transfers the mannosyl residue from (Guanosine Diphosphate –mannose) GDP-mannose to DolP. The DPM1 gene encoding the DPM synthase in S. cerevisiae and the protein have been characterized [8,9], and homologous genes from Ustilago maydis and Trypanosoma brucei have been reported [10,11]. The homologs from humans, Schizosacchromyces pombe and Trichoderma reesei [12,13], were found to form a separate class of the enzyme lacking the C-terminal transmembrane domain present in S. cerevisiae, U. maydis, and T. brucei synthases (Figure 1). Maeda et al [14] reported that the DPM synthase from humans forms a complex of three subunits, DPM1, DPM2 and DPM3, where DPM1 is the catalytic subunit, DPM2 regulates its activity, and DPM3 anchors the complex in the ER membrane. It has been established that if a Dpm protein lacks a transmembrane domain, it cannot attach to the ER membrane and—to be
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