Moorthy Anu K, Savinova Olga V, Ho Jessica Q, Wang Vivien Ya-Fan, Vu Don, Ghosh Gourisankar
Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, 92093, USA.
EMBO J. 2006 May 3;25(9):1945-56. doi: 10.1038/sj.emboj.7601081. Epub 2006 Apr 13.
The NF-kappaB p50 is the N-terminal processed product of the precursor, p105. It has been suggested that p50 is generated not from full-length p105 but cotranslationally from incompletely synthesized molecules by the proteasome. We show that the 20S proteasome endoproteolytically cleaves the fully synthesized p105 and selectively degrades the C-terminus of p105, leading to p50 generation in a ubiquitin-independent manner. As small as 25 residues C-terminus to the site of processing are sufficient to promote processing in vivo. However, any p105 mutant that lacks complete ankyrin repeat domain (ARD) is processed aberrantly, suggesting that native processing must occur from a precursor, which extends beyond the ARD. Remarkably, the mutant p105 that lacks the internal region including the glycine-rich region (GRR) is completely degraded by 20S proteasome in vitro. This suggests that the GRR impedes the complete degradation of the p105 precursor, thus contributing to p50 generation.
核因子κB p50是前体p105的N端加工产物。有人提出，p50不是由全长p105产生的，而是由蛋白酶体从未完全合成的分子中进行共翻译产生的。我们发现，20S蛋白酶体以内切蛋白酶的方式切割完全合成的p105，并选择性地降解p105的C端，从而以不依赖泛素的方式产生p50。加工位点C端小至25个残基就足以促进体内加工。然而，任何缺乏完整锚蛋白重复结构域（ARD）的p105突变体都会发生异常加工，这表明天然加工必须从前体发生，该前体延伸至ARD之外。值得注意的是，缺乏包括富含甘氨酸区域（GRR）在内的内部区域的突变体p105在体外被20S蛋白酶体完全降解。这表明GRR阻碍了p105前体的完全降解，从而有助于p50的产生。
