Andrew N. Binns
Carolyn Hoff Lynch Term Professor

Microbiology, Virology and Parasitology Program

Address

204D Carolyn Lynch Labs
433 S. University Ave
Philadelphia, PA 19104-6018

Office tel.: 215 898-8684
Lab tel.: 215 898-6875
Fax: 215 898-8780
E-mail: abinns@sas.upenn.edu

Link(s)

Dr. Binns's Biology Faculty Profile

Education

Lawrence University: BA (Biology), 1971.

Princeton University: PhD (Developmental Biology and Genetics), 1979.

Rockefeller University: Postdoctoral Research (Plant/Pathogen Interactions), 1978-1980.

Research Interests

• Type IV secretion systems
• Macromolecular transport from bacteria to bacteria and bacteria to plants
• Regulation of gene expression in bacteria by two component systems.

Key words: Type IV secretion system, conjugation, two component regulatory systems, Agrobacterium tumefaciens.

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Description of Research

Agrobacterium tumefaciens is a gram-negative soil bacterium that has the unique capacity to transfer DNA from its resident Ti (tumor-inducing) plasmid, and proteins encoded by this plasmid, into plant cells. The transferred DNA (the T-DNA) is ultimately moved into the nucleus, integrated into the chromosomal DNA and expressed. T-DNA expression results in the production of growth factors that cause uncontrolled cell proliferation. Intriguingly, transport of the T-DNA and virulence proteins is mediated by the paradigm Type IV secretion system, the VirB complex. Related Type IV systems are involved in conjugal plasmid transfer between bacteria and transfer of virulence factors from a wide variety of both plant and animal pathogens to host cells. The research in our laboratory focuses on the following questions:

• How are the transported DNA and protein molecules moved out of Agrobacterium and into the plant cell? In these studies we are focusing on genetic and physical analysis of the VirB complex and the domains of the virulence proteins, such as VirE2, that are necessary for transport by the complex.
• What are the features of recipient cells that are involved in Type IV mediated transport? This question is particularly relevant in conjugal plasmid transfer, where only limited information is available despite the importance of such transfer in the spread of antibiotic resistance. Our studies to date have identified ways in which virB-mediated conjugal transfer between A. tumefaciens strains can be either drastically increased or drastically reduced. We are now studying recently identified genes that are required for the capacity of a cell to serve as a recipient. In addition, we are carrying out similar investigations on recipient E. coli in conjugal transfer mediated by wide host range type plasmids, such as RK2.
• How are plant derived signals recognized and how does this recognition activate the expression of the virulence genes? Initiation of plant transformation by Agrobacterium occurs when the virulence (vir) genes of the Ti plasmid are activated. This occurs as a result of the activities of a classic two component regulatory system. The sensor kinase (VirA), a membrane bound dimeric histidine kinase responds to plant derived compounds (certain sugars, phenolics and low pH) by phosphorylating the response regulator (VirG) which, in turn, activates transcription of the vir genes. We are particularly interested in how the different signals are recognized by and stimulate the capacity of the VirA sensor kinase to phosphorylate VirG.

Recent Publications

Liu, Z. and A. N. Binns. 2003. Functional subsets of the VirB Type IV transport complex proteins of Agrobacterium tumefaciens. J. Bacteriol. 185:3259-3269

Nair, G., Z. Liu and A. N. Binns. 2003. Re-examining the role of the accessory plasmid pAtC58 in the virulence of Agrobacterium tumefaciens strain C58. Plant Physiol. 133:989-999

Wise, A. A., L. Voinov, and A. N. Binns. 2005. Intersubunit complementation of sugar signal transduction in VirA heterodimers and post-translational regulation of VirA activity in Agrobacterium tumefaciens. J. Bacteriol. 187:213-223

Cascales, E., K. Atmakuri, Z. Liu A. N. Binns and P. J. Christie. 2005. Agrobacterium tumefaciens oncogenic suppressors inhibit T-DNA and VirE2 protein substrate binding to the VirD4 coupling protein. Mol. Microbiol. 58:565-579

McCullen, C. A. and A. N. Binns. 2006. Interactions between Agrobacterium tumefaciens and plant cells required for interkingdom macromolecular transfer. Ann. Rev. Cell and Devel. Biol. 22:101-127

Lab

Rotation Projects for 2006-2007

• Examine the “response character” (i.e. on/off vs. graded response) of the VirA sensor kinase to various signals and determine how signal integration by VirA may affect this phenotype.
• Utilize fluorescence microscopy to examine the activation of signal inducible GFP constructs within the plant in order to map a distribution of the various signals that activate vir gene expression.
• Characterize the physical interaction between a periplasmic protein (ChvE) that binds sugars and the periplasmic domain of VirA, which responds to sugars in a ChvE-mediated fashion.
• Utilize the yeast two hybrid system to search for chromosomally encoded proteins that interact with the VirB Type IV secretion system and use genetic methods to characterize their importance in the transport process.

Lab personnel:

Gauri Nair (Graduate Student, Biology)
Dr. Arlene Wise (Research Associate)
Dr. Zhenying Liu (Research Associate)
Fanglian He (Graduate Student, Biology)