Structure of the heterotrimeric complex that regulates type III secretion needle formation

doi:10.1073/pnas.0610098104

Structure of the heterotrimeric complex that regulates type III secretion needle formation

*Institut de Biologie Structurale Jean-Pierre Ebel, 41 Rue Jules Horowitz, Unité Mixte de Recherche 5075, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Université Joseph Fourier, 38027 Grenoble, France; and
^†Institut de Recherches en Technologie et Sciences pour le Vivant, Unité Mixte de Recherche 5092, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Université Joseph Fourier, 38054 Grenoble, France

Edited by John Kuriyan, University of California, Berkeley, CA, and approved March 21, 2007 (received for review November 14, 2006)

Abstract

Type III secretion systems (T3SS), found in several Gram-negative pathogens, are nanomachines involved in the transport of virulence effectors directly into the cytoplasm of target cells. T3SS are essentially composed of basal membrane-embedded ring-like structures and a hollow needle formed by a single polymerized protein. Within the bacterial cytoplasm, the T3SS needle protein requires two distinct chaperones for stabilization before its secretion, without which the entire T3SS is nonfunctional. The 2.0-Å x-ray crystal structure of the PscE-PscF^55–85-PscG heterotrimeric complex from Pseudomonas aeruginosa reveals that the C terminus of the needle protein PscF is engulfed within the hydrophobic groove of the tetratricopeptide-like molecule PscG, indicating that the macromolecular scaffold necessary to stabilize the T3SS needle is totally distinct from chaperoned complexes between pilus- or flagellum-forming molecules. Disruption of specific PscG–PscF interactions leads to impairment of bacterial cytotoxicity toward macrophages, indicating that this essential heterotrimer, which possesses homologs in a wide variety of pathogens, is a unique attractive target for the development of novel antibacterials.

Footnotes

^‡To whom correspondence may be addressed. E-mail: ina.attree-delic{at}cea.fr or andrea.dessen{at}ibs.fr
Author contributions: I.A. and A.D. designed research; M.Q., S.P., V.J., C.C.-M., J.-P.S., I.A., and A.D. performed research; M.Q., V.J., I.A., and A.D. analyzed data; and A.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The atomic coordinates listed in this paper have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 2UWJ).
This article contains supporting information online at www.pnas.org/cgi/content/full/0610098104/DC1.
Abbreviations:

T3SS,

type III secretion systems;

TPR,

tetratricopeptide.