Characterization of the interaction between RssB and the anti-adaptor proteins in Escherichia coli

Wednesday, October 26, 2011 — Poster Session IV
2:00 p.m. – 4:00 p.m.	Natcher Conference Center	NCI	VIROL/MICRO-4

* FARE Award Winner

Authors

• A Battesti
• P Milanesio
• JR Hoskins
• S Wickner
• S Gottesman

Abstract

RpoS is a highly regulated sigma factor in E. coli. In favorable growth conditions, RpoS interacts with the adaptor protein RssB that allows its degradation by the ClpXP protease. RssB can be phosphorylated, but the role of its phosphorylation is unclear. Under stress conditions, RpoS degradation is prevented by the titration of RssB by proteins called “anti-adaptors”. Although these proteins share a common function, we show here that they use distinct mechanisms to protect RpoS from degradation. Indeed, IraP and IraD interact with the RssB N-terminal domain whereas IraM interacts with its C-terminal part. Moreover, RssB mutants impaired in their ability to be phosphorylated do not interact with IraP but still interact with IraD and IraM, suggesting that the anti-adaptors interact with different forms of RssB. Finally, by screening a library of RssB random mutants for those unable to bind IraP, two functional regions of RssB were defined. The first region, in the RssB N-terminal domain, confirms the involvement of phosphorylation in IraP interaction. The second region, in the RssB C-terminal, is involved in allosteric changes allowing RssB to deliver RpoS to the protease. These experiments have uncovered unexpected complexity in the ways in which the anti-adaptors modulate RssB activity.

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