earticle

영어

Protein O-mannosylation is evolutionarily conserved essential protein modification from bacteria to humans, which is initiated in the ER by protein O-mannosyltransferases (PMTs) that catalyze the transfer of mannose from Dol-P-Man to Ser/Thr residues of secretory proteins. We identified and characterized five PMT subfamily genes, PMT1.1, PMT1.2, PMT2, PMT4 and PMT6 in the thermotolerant methylotrophic yeast Hansenula polymorpha. The hydropathy profile analysis predicts all H. polymorpha Pmt proteins to be integral membrane proteins with multiple transmembrane domains. For confirmation of subcellular localization of HpPmt proteins and characterization of PMT complexes, we constructed a set of HA or FLAG epitope-tagged versions of H. polymorpha Pmt proteins. All the C-terminal epitope-tagged HpPmt proteins were shown to be fully functional in vivo and to localize at the ER/Golgi membrane, except for Pmt6p. The significant sensitivity of Hppmt1.2 strain to the PMT1 inhibitor R3A-1c suggested that HpPMT1.2 might have a minor function redundant with HpPMT1.1. However, co-immunoprecipitation experiments using monoclonal anti-HA or anti-Flag bead revealed the complex formation between HpPmt1.1p and HpPmt2p, but no interaction between HpPmt1.2p and HpPmt2p even in the absence of HpPmt1.1p. The results strongly support the notion that interaction with HpPmt2p is required for the full mannosyltransferase activity of HpPmt1.1p, which plays a major role in O-mannosylation essential for cell wall integrity in H. polymorpha.