Gary Roberts
Professor of Bacteriology
- Address:
- 5155 Microbial Sciences Building
- Telephone:
- 262-3567
- Email:
- groberts@bact.wisc.edu
- Research Fields:
- Gene Expression
- Microbial Genetics
Ph.D., Univ. of California-Berkeley, 1978
Postdoctoral Research: University of Wisconsin-Madison
Research Interests
Our laboratory studies two different regulatory processes that are both involved in the central metabolism of the bacterium Rhodospirillum rubrum.
Research Description
The first project concerns CooA, a dimeric bacterial heme protein that binds carbon monoxide (CO) and, in response, undergoes a conformational change that allows it to bind specific DNA sequences and activate transcription of genes whose products are involved in the oxidation of CO. CooA is very interesting for a variety of reasons: (i) It is a specific sensor of CO in that it either fails to bind other small molecule effectors or fails to undergo the proper conformational change upon binding. (ii) CooA is also a redox sensor in that it only binds CO when its heme is reduced; the redox sensing involves a highly unusual switch in the protein ligands to the heme. This mechanism of redox sensing is unique among examined proteins (iii) The structure of reduced (but CO-free) CooA has been solved by the Poulos group at UC-Irvine and it reveals that the N-terminal proline of the other protein monomer serves as a ligand to each heme; proline has never before been seen as a heme ligand. (iv) CooA is a homolog of CRP, the E. coli protein that binds cAMP and regulates expression of genes whose products are involved in carbon utilization. Only the structure of the cAMP-bound form of CRP has been known and the CO-free structure of CooA therefore provides an insight into the conformational change in both proteins upon activation. We are employing a combination of genetics, protein biochemistry, spectroscopy and crystallography to understand these processes at the molecular level.
The second project involves PII, one of the most broadly distributed regulatory protein in nature. It is involved in central nitrogen regulation in almost all known prokaryotes and has been shown to be present in the chloroplasts of plants and algae. PII appears to exert its regulatory properties by binding ATP and 2-ketoglutarate and the interacting with different proteins and affecting their activity. The exact basis for these protein-protein interactions remains unknown, nor is it understood why there are different PII homologs, with somewhat different functions, in many prokaryotes. R. rubrum has three such homologs and we are dissecting the molecular basis for their different properties using genetics, physiology and biochemical assays; this work is all informed by the structural analysis of the Ollis group in Australia.
Representative Publications
- Youn, H., Kerby, R.L., Conrad, M. and Roberts, G.P. 2006. Study of highly constitutively active mutants suggests how cAMP activates cAMP receptor protein. J. Biol. Chem. In press.
- Clark, R.W., Lanz, N.D., Lee, A.J., Kerby, R.L., Roberts, G.P. and Burstyn, J.N. 2006. Unexpected NO-dependent DNA Binding by the CooA Homolog from C. hydrogenoformans. Proc. Natl. Acad Sci. USA. In press.
- Zhu, Y., Conrad,M.C., Zhang, Y., and Roberts, G.P. 2006. Identification of Rhodospirillum rubrum GlnB variants that are altered in their ability to interact with different targets in response to nitrogen-status signals. J. Bacteriol. In press.
- Zhang, Y., Pohlmann, E.L. and Roberts, G.P. 2005. GlnD is essential for NifA activation, NtrB/NtrC-regulated gene expression and the posttranslational regulation of nitrogenase activity in photosynthetic, nitrogen-fixing bacterium Rhodospirillum rubrum. J. Bacteriol. 187:1254-1265.
- Youn, H., Thorsteinsson, M.V., Kerby, R.L., Conrad, M. and Roberts, G.P. 2005. Dual roles of an E-helix residue, Glu167, in the transcriptional activator function of CooA. J. Bacteriol. 187:2573-2581.