tailieunhanh - Báo cáo khóa học: NUB1-mediated targeting of the ubiquitin precursor UbC1 for its C-terminal hydrolysis

NEDD8 is a ubiquitin-like protein that controls vital bio-logical events through its conjugation to target proteins. Previously, we identifieda negative regulator oftheNEDD8 conjugation system, NEDD8 ultimate buster-1 (NUB1), that recruits NEDD8 and its conjugates to the proteasome for degradation. Recently, we performed yeast two-hybrid screening with NUB1 as bait and isolated a ubiquitin pre-cursor UbC1 that is composed ofnine tandem repeats of a ubiquitin unit through a-peptide bonds. | Eur. J. Biochem. 271 972-982 2004 FEBS 2004 doi NUB1-mediated targeting of the ubiquitin precursor UbC1 for its C-terminal hydrolysis Tomoaki Tanaka Edward T. H. Yeh and Tetsu Kamitani Department of Cardiology University of Texas M. D. Anderson Cancer Center and Institute of Molecular Medicine University of Texas-Houston Health Science Center Houston Texas USA NEDD8 is a ubiquitin-like protein that controls vital biological events through its conjugation to target proteins. Previously we identified a negative regulator of the NEDD8 conjugation system NEDD8 ultimate buster-1 NUB1 that recruits NEDD8 and its conjugates to the proteasome for degradation. Recently we performed yeast two-hybrid screening with NUB1 as bait and isolated a ubiquitin precursor UbC1 that is composed of nine tandem repeass of a ubiquitin unit through a-peptide bonds. Interestingly NUB1 interacted with UbC1 through its UBA domain. Further study revealed that the UBA domain interacted with a-peptide bond-linked polyubiquitin but not with isopeptide bond-linked polyubiquitin indicating that the UBA domain ofNUB1 is a specific acceptor ofr the linear ubiquitin precursor. A functional study revealed that an unidentified protein that was immunoprecipitated with NUB1 served as a ubiquitin C-terminal hydrolase for UbC1. Thus NUB1 seems to form a protein complex with the unidentified ubiquitin C-terminal hydrolase and recruit UbC1 to this complex. This might allow the ubiquitin C-terminal hydrolase to hydrolyze UbC1 in order to generate ubiquitin monomers. Northern blot analysis showed that the mRNAs ofboth NUB1 and UbC1 were enriched in the testis. Furthermore in situ hybridization showed that both mRNAs were strongly expressed in seminiferous tubules ofthe testis. These results may imply that the UbC1 hydrolysis mediated by NUB1 is involved in cellular functions in the seminiferous tubules such as spermatogenesis. Keywords NUB1 ubiquitin UBA ubiquitin C-terminal .