Journal of Biochemistry Advance Access published online on January 7, 2008
Journal of Biochemistry, doi:10.1093/jb/mvm249
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© 2008 The Japanese Biochemical Society
O-mannosylation is required for degradation of the endoplasmic reticulum-associated degradation substrate Gas1*p via the ubiquitin/proteasome pathway in Saccharomyces cerevisiae
1Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8566, Japan
2Graduate School of Life and Environmental Science, University of Tsukuba, Tsukuba, Ibaraki 305-8752, Japan
*To whom correspondence should be addressed: Dr. Yoshifumi Jigami: Tel: +81-29-861-6160, Fax: +81-29-861-6161, E-mail: jigami.yoshi{at}aist.go.jp
Received November 22, 2007; Accepted December 26, 2007
| Abstract |
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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· pmt2· 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.
Key Words: ERAD, Gas1*p, O-mannosylation, PMT, post-ER degradation
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