期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：33
页码：12136-12141
DOI：10.1073/pnas.0404733101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The ssrA-degradation tag sequence contains contiguous binding sites for the SspB adaptor and the ClpX component of the ClpXP protease. Although SspB normally enhances ClpXP degradation of ssrA-tagged substrates, it inhibits proteolysis under conditions that prevent tethering to ClpX. By increasing the spacing between the protease and adaptor-binding determinants in the ssrA tag, substrates were obtained that displayed improved SspB-mediated binding to and degradation by ClpXP. These extended-tag substrates also showed significantly reduced conditional inhibition but bound SspB normally. Both wild-type and mutant tags showed highly dynamic SspB interactions. Together, these results strongly support delivery models in which SspB and ClpX bind concurrently to the ssrA tag, but also suggest that clashes between SspB and ClpX weaken simultaneous binding. During substrate delivery, this signal masking is overcome by tethering SspB to ClpX, which ensures local concentrations high enough to drive tag engagement. This obstruct-then-stimulate mechanism may have evolved to allow additional levels of regulation and could be a common trait of adaptor-mediated protein degradation.
