O-mannosylation is required for degradation of the endoplasmic reticulum-associated degradation substrate Gas1*p via the ubiquitin/proteasome pathway in Saccharomyces cerevisiae.
In Saccharomyces cerevisiae, protein O-mannosylation, which is executed by protein O-mannosyltransferases, is essential for a variety of biological processes as well as for conferring solubility to misfolded proteins. To determine if O-mannosylation plays an essential role in endoplasmic reticulum-associated degradation (ERAD) of misfolded proteins, we used a model misfolded protein, Gas1*p. The O-mannose content of Gas1*p, which is transferred by protein O-mannosyltransferases, was higher than that of Gas1p. Both Pmt1p and Pmt2p, which do not transfer O-mannose to correctly folded Gas1p, participated in the O-mannosylation of Gas1*p. Furthermore, in a pmt1 Delta pmt2 Delta double-mutant background, degradation of Gas1*p is altered from a primarily proteasome dependent to a vacuolar protease-dependent pathway. This process is in a manner dependent on a Golgi-to-endosome sorting function of the VPS30 complex II. Collectively, our data suggest that O-mannosylation plays an important role for proteasome-dependent degradation of Gas1*p via the ERAD pathway and when O-mannosylation is insufficient, Gas1*p is degraded in the vacuole. Thus, we propose that O-mannosylation by Pmt1p and Pmt2p might be a key step in the targeting of some misfolded proteins for degradation via the proteasome-dependent ERAD pathway.
Hirayama
Hiroto
H
Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
Fujita
Morihisa
M
Yoko-o
Takehiko
T
Jigami
Yoshifumi
Y
D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006868:Hydrolysis; D008358:Mannose / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
C066709:GAS1 protein, S cerevisiae; D008562:Membrane Glycoproteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex; D008358:Mannose