This Article Full Text Full Text (PDF) Other Versions of this Article: JB.00513-07v1 189/18/6626    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Haft, R. J. F. Articles by Traxler, B. Search for Related Content PubMed PubMed Citation Articles by Haft, R. J. F. Articles by Traxler, B.

In Vivo Oligomerization of the F Conjugative Coupling Protein TraD

Rembrandt J. F. Haft,¹ Eliora G. Gachelet,¹ Tran Nguyen,¹ Luttrell Toussaint,¹ Dylan Chivian,^2, and Beth Traxler^1*

Department of Microbiology, University of Washington, Seattle, Washington 98195,¹ Department of Biochemistry, University of Washington, Seattle, Washington 98195²

Received 3 April 2007/ Accepted 5 July 2007

Type IV secretory systems are a group of bacterial transporters responsible for the transport of proteins and nucleic acids directly into recipient cells. Such systems play key roles in the virulence of some pathogenic organisms and in conjugation-mediated horizontal gene transfer. Many type IV systems require conserved "coupling proteins," transmembrane polypeptides that are critical for transporting secreted substrates across the cytoplasmic membrane of the bacterium. In vitro evidence suggests that the functional form of coupling proteins is a homohexameric, ring-shaped complex. Using a library of tagged mutants, we investigated the structural and functional organization of the F plasmid conjugative coupling protein TraD by coimmunoprecipitation, cross-linking, and genetic means. We present direct evidence that coupling proteins form stable oligomeric complexes in the membranes of bacteria and that the formation of some of these complexes requires other F-encoded functions. Our data also show that different regions of TraD play distinct roles in the oligomerization process. We postulate a model for in vivo oligomerization and discuss the probable participation of individual domains of TraD in each step.

Published ahead of print on 13 July 2007.

Present address: Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720.