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Published online 9 January 2006. doi:10.1083/jcb.200507149
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 172, Number 2, 211-219
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Article

The Png1–Rad23 complex regulates glycoprotein turnover



Ikjin Kim1, Jungmi Ahn1, Chang Liu1, Kaori Tanabe2, Jennifer Apodaca1, Tadashi Suzuki2, and Hai Rao1

1 Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78245
2 Department of Biochemistry and 21st Century Center of Excellence Program, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan

Correspondence to Hai Rao: raoh{at}uthscsa.edu

Misfolded proteins in the endoplasmic reticulum (ER) are destroyed by a pathway termed ER-associated protein degradation (ERAD). Glycans are often removed from glycosylated ERAD substrates in the cytosol before substrate degradation, which maintains the efficiency of the proteasome. Png1, a deglycosylating enzyme, has long been suspected, but not proven, to be crucial in this process. We demonstrate that the efficient degradation of glycosylated ricin A chain requires the Png1–Rad23 complex, suggesting that this complex couples protein deglycosylation and degradation. Rad23 is a ubiquitin (Ub) binding protein involved in the transfer of ubiquitylated substrates to the proteasome. How Rad23 achieves its substrate specificity is unknown. We show that Rad23 binds various regulators of proteolysis to facilitate the degradation of distinct substrates. We propose that the substrate specificity of Rad23 and other Ub binding proteins is determined by their interactions with various cofactors involved in specific degradation pathways.

Abbreviations used in this paper: CPY, carboxypeptidase Y; EndoH, endoglycosidase H; ERAD, ER-associated protein degradation; MHC, myosin heavy chain; RTA, ricin A chain; Ub, ubiquitin; UBA, Ub-associated; UBL, Ub-like; XPCB, XPC binding; UFD, Ub fusion degradation.


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