1. Department of Tumor Immunology, Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113-8613, Japan
2. Department of Molecular Oncology, Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113-8613, Japan
3. CREST, Japan Science and Technology Corporation (JST), Saitama 332-0012, Japan,
4. Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka 545-8585, Japan
5. Kihara Institute for Biological Research, Graduate School of Integrated Science, Yokohama City University, Yokohama, Kanagawa 244-0813, Japan
6. Synthetic Cellular Chemistry Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
7. Chemical Genetics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
8. Department of Functional Materials Science, Saitama University, Saitama, 338-8570, Japan

Correspondence to: Keiji Tanaka^2,3Tadashi Tai¹ Correspondence and requests for materials should be addressed to T.T. (e-mail: Email: tai@rinshoken.or.jp) or K.T. (e-mail: Email: tanakak@rinshoken.or.jp).

Abstract

N-glycosylation of proteins in the endoplasmic reticulum (ER) has a central role in protein quality control^{1, 2, 3}. Here we report that N-glycan serves as a signal for degradation by the Skp1–Cullin1–Fbx2–Roc1 (SCF^Fbx2) ubiquitin ligase complex. The F-box protein Fbx2 (ref. 4) binds specifically to proteins attached to N-linked high-mannose oligosaccharides and subsequently contributes to ubiquitination of N-glycosylated proteins. Pre-integrin 1 is a target of Fbx2; these two proteins interact in the cytosol after inhibition of the proteasome. In addition, expression of the mutant Fbx2F, which lacks the F-box domain that is essential for forming the SCF complex, appreciably blocks degradation of typical substrates of the ER-associated degradation pathway^{5, 6}. Our results indicate that SCF^Fbx2 ubiquitinates N-glycosylated proteins that are translocated from the ER to the cytosol by the quality control mechanism.