macromolecular transport processes during pathogenesis

Translocation of macromolecules between cells is a major area of biomedical interest. The focus of study in this laboratory is a type IV secretion (T4S) system of Agrobacterium tumefaciens. This system is ancestrally related and functionally similar to bacterial conjugation systems, as well as recently described protein translocation systems used by bacterial pathogens during the course of infection This T4S system mediates transfer of diverse substrates including oncogenic DNA and other DNA in the form of nucleoprotein particles, and of protein monomers across the A. tumefaciens cell envelope. These substrates are delivered to a variety of phylogenetically-diverse target bacterial or eukaryotic cells through a process dependent on direct cell-to-cell contact. This T4S system, assembled from VirD4 and 11 VirB subunits, is an especially attractive system for detailed mechanistic studies of macromolecular transport because of the ease of manipulation of A. tumefaciens, the large numbers of strains, constructs, and other molecular tools at hand, and the wealth of information about it and closely related transfer systems. We also are developing studies of other T4S systems of Gram-negative and Gram-positive bacterial pathogens.

The overall goal of work in this laboratory is to describe in detailed mechanistic terms the dynamic processes required for biogenesis and function of T4S systems during infection. We use powerful in vivo technologies developed in this laboratory and other state-of-the art biochemical and structure-based approaches to define how DNA and protein substrates are recruited to and translocated through the T4S channels.

Questions of particular interest at this time include:
1. How do three ATPase subunits energize machine assembly or function?
2. How are substrates recruited to the secretion channel?
3. What is the route of substrate transfer through the secretory apparatus?
4. How do bacterial cells establish contact with bacterial or eukaryotic target cells to mediate intercellular substrate transfer?
5. What are the cellular consequences of substrate trafficking in the host cell?

SELECTED PUBLICATIONS:

Christie PJ, Atmakuri K, Jakubowski S, Krishnamoorthy V, and Cascales E (2005). Biogenesis, architecture, and function of bacterial type IV secretion systems. Annu. Rev. Microbiol.59:451-485

Jakubowski S, Cascales E, Krishnamoorthy V, and Christie PJ (2005). Agrobacterium tumefaciens VirB9, an outer-membrane-associated component of a type IV secretion system, regulates substrate selection and T-pilus biogenesis J. Bacteriol.187:3486-3495 [abstract]

Christie PJ and E. Cascales E. (2005). Structural and dynamic properties of bacterial type IV secretion systems. Molecular Membrane Biology (Thematic Issue on Translocation of Proteins across Membranes). 22:51-61 [abstract]

Cascales E, and Christie PJ. (2004). Definition of a bacterial type IV secretion pathway for a DNA substrate. Science 304:1170-1173. [abstract]

Christie PJ, and Covacci A. (2004). Bacterial type IV secretion systems: DNA conjugation machines for export of virulence factors. In P. Cossart, P. Boquet, S. Normark, R. Rappuoli (eds.), Cellular Microbiology 2nd edition, ASM Press, pp. 393-408.

Christie PJ (2004). The Agrobacterium Ti plasmids. In Funnell B and Phillips G (eds.). Ch. 22. pp. 455-472. The Biology of Plasmids, ASM Press, 2004.

Jakubowski SS, Cascales E, and Christie PJ (2004). Agrobacterium tumefaciens VirB6 domains direct the ordered export of a DNA substrate through a type IV secretion system. J. Mol. Biol. 341:961-977. [abstract]

Atmakuri K, Cascales E, and Christie PJ (2004). Energetic components VirD4, VirB11 and VirB4 mediate early DNA transfer reactions required for bacterial type IV secretion. Mol. Microbiol. 54:1199-1211. [abstract]

Cascales E, and Christie PJ (2004). Agrobacterium VirB10, an ATP energy sensor required for type IV secretion. Proc. Natl. Acad. Sci. USA 101:17228-17233. [abstract]

Christie PJ (2004). Type IV secretion: the Agrobacterium virB/D4 and related conjugation systems. Biochem. Biophys. Acta. 1694:219-234 (Thematic Issue on Protein Export/Secretion in Bacteria). [abstract]

Cascales E, and Christie PJ (2003). The versatile bacterial type IV secretion systems. Nat. Rev. Microbiol. 1:137-150. [abstract]

Ding Z, Atmakuri K, and Christie PJ (2003). The outs and ins of bacterial type IV secretion substrates. Trends Microbiol. 11:527-535. [abstract]

Atmakuri K, Ding Z, and Christie PJ (2003). VirE2, a type IV secretion substrate, interacts with the VirD4 transfer protein at cell poles of Agrobacterium tumefaciens. Mol. Microbiol. 49:1699-1713. [abstract]

Ding Z, and Christie PJ (2003). Agrobacterium tumefaciens twin-arginine-dependent translocation is important for virulence, flagellation, and chemotaxis but not type IV secretion. J. Bacteriol. 185:760-771. [abstract]

[compete list of publications on PubMed]