Rhomboid protease AarA mediates quorum-sensing in Providencia stuartii by activating TatA of the twin-arginine translocase

doi:10.1073/pnas.0608140104

Rhomboid protease AarA mediates quorum-sensing in Providencia stuartii by activating TatA of the twin-arginine translocase

*Department of Microbiology and Immunology, Emory University School of Medicine, 1510 Clifton Road NE, Atlanta, GA 30322;
^†Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom; and
^‡Research Service, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30033

Edited by Bonnie L. Bassler, Princeton University, Princeton, NJ, and approved November 20, 2006 (received for review September 15, 2006)

Abstract

The Providencia stuartii AarA protein is a member of the rhomboid family of intramembrane serine proteases and is required for the production of an unknown quorum-sensing molecule. In a screen to identify rhomboid-encoding genes from Proteus mirabilis, tatA was identified as a multicopy suppressor and restored extracellular signal production as well as complementing all other phenotypes of a Prov. stuartii aarA mutant. TatA is a component of the twin-arginine translocase (Tat) protein secretion pathway and likely forms a secretion pore. By contrast, the native tatA gene of Prov. stuartii in multicopy did not suppress an aarA mutation. We find that TatA in Prov. stuartii has a short N-terminal extension that was atypical of TatA proteins from most other bacteria. This extension was proteolytically removed by AarA both in vivo and in vitro. A Prov. stuartii TatA protein missing the first 7 aa restored the ability to rescue the aarA-dependent phenotypes. To verify that loss of the Tat system was responsible for the various phenotypes exhibited by an aarA mutant, a tatC-null allele was constructed. The tatC mutant exhibited the same phenotypes as an aarA mutant and was epistatic to aarA. These data provide a molecular explanation for the requirement of AarA in quorum-sensing and uncover a function for the Tat protein export system in the production of secreted signaling molecules. Finally, TatA represents a validated natural substrate for a prokaryotic rhomboid protease.

Footnotes

^§To whom correspondence should be addressed. E-mail: prather{at}emory.edu
Author contributions: L.G.S., K.S., and P.N.R. designed research; L.G.S., K.S., K.M.C., and S.B. performed research; M.F. and P.N.R. analyzed data; and M.F. and P.N.R. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. DQ989793).
Abbreviations:

CM,

conditioned media;

DDM,

n-dodecyl-β-d-maltoside;

Tat,

twin-arginine translocase;

TMAO,

trimethylamine-N-oxide.