Binding with intent to destroy : RssB adaptor function in Clp-XP-mediated proteolysis of sigmaS

Severe stress results in global changes in the bacterial proteome. To respond effectively, new proteins must be synthesized, others destroyed. Coordinated changes in protein synthesis often result from the engagement of an alternate a subunit with the RNA core polymerase. The as subunit of the RNA polymerase is a master stress response regulator in E. coli. Under satisfactory growth conditions, proteolysis keeps the levels of as low; upon stress, various mechanisms converge to raise the levels as. In this work we focus on the facilitated delivery of as to the ClpXP protease. Proteolysis of as by ClpXP requires the accessory factor RssB. RssB is a two-component response regulator. Not surprisingly, its activity is positively regulated by phosphorylation of a conserved aspartate in its receiver domain. Whereas most response regulators are transcription factors, however, RssB is an adaptor protein. RssB binds to as, promoting a conformational change in as that exposes its N-terminal ClpX recognition motif. RssB also contacts ClpXP itself, enabling the formation of a quaternary degradative complex. Following the degradation of as, RssB is released. This work addresses two outstanding questions regarding RssB-mediated proteolysis of [sigma]s: 1) the requirement of RssB phosphorylation for [sigma]s degradation; and 2) the mechanism of RssB interaction with ClpXP. Previous studies have shown that phosphorylation of RssB increases its affinity for [sigma]s. Initially, phosphorylation of RssB was thought to be a pre-requisite for [sigma]s binding; more recently this has come under some debate. Our data demonstrate that phosphorylation is not strictly required for RssB function.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Ebrahim, Shamsah

Advisor dc:contributor.advisor

• Tania A. Baker.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/40959

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/40959