Assistant Professor

Biology Department
Chemistry and Biological Chemistry Department

Education and Training

Ph.D. National University of Mexico
Biochemistry

Postdoctoral Training: University of Illinois at Urbana-Champaign, University of Helsinki.

Contact

E-mail: barqub@rpi.edu
Phone: (518) 276-3861
Fax: (518) 276-2851

Office: Center for Biotechnology and Interdisciplinary Studies Rm. 2239
Lab: Center for Biotechnology and Interdisciplinary Studies Rm. 2444

Rensselaer Polytechnic Institute
110 8th Street,
Troy, NY 12180

Research Interests

Bioenergetics, Biochemistry, Biophysics, Membrane proteins, Bacterial physiology.

The main emphasis of the research in my laboratory approaches Na⁺ bioenergetics in bacteria on a number of levels, from global gene expression studies and bacterial physiology to biochemistry and mechanistic enzymology. We are initially focusing on Vibrio cholerae, which is an important pathogen and it is congenial to genetic manipulation.

1. Mechanistic enzymology of primary sodium pumps. We focus on two enzymes that create sodium gradient: the Na⁺ translocating NADH:quinone oxidoreductase, (Na⁺-NQR) and the Na⁺ translocating NADH:ferredoxin oxidoreductase (Rnf). Na⁺-NQR is the entry point for electrons into the respiratory chain in many pathogens including Vibrio cholerae and Yersinia pestis. We aim to elucidate the mechanism by which redox reactions are harnessed to drive the translocation of sodium in Na⁺-NQR. To this end, we are studying both the redox processes and the mechanism of sodium transport by an approach that combines site-directed mutagenesis with kinetics and other biophysical methods. Rnf belongs to a diverse family of membrane proteins widely distributed among bacteria that share homology to Na⁺-NQR. Although little is known about their mechanism, the enzymes in this group appear to function as energy transducers and likely, some of Rnf’s are redox driven sodium transporters. Furthermore, Rnf appears to be an essential enzyme in some bacteria, making it a potential drug target.  By studying these two enzymes, Na⁺-NQR and Rnf in parallel, we expect that their similarities and differences will help to elucidate a general mechanism of redox driven sodium translocation, and to understand the physiological role of these enzymes.

2. The role of sodium and proton gradients in the bioenergetics of Vibrio cholerae and Yersinia pestis: adaptation at the chemiosmotic level. Most organisms use proton gradients, generated by aerobic respiration, as the main bioenergetic currency. However, in some bacteria sodium gradients seem to play an important role in energy transduction. Vibrio cholerae and Yersinia pestis are two examples of bacteria where both proton and sodium gradients appear to be used, either under different growth conditions or for different functions in the cell. We are measuring the internal and external ion concentrations (H⁺, Na⁺, etc.) as well as the electrical component of the membrane potentials in cells grown in different conditions. We hope to obtain a more complete picture of how sodium and proton gradients interact in bacterial bioenergetics.

Selected Publications

Duffy, E.B., and *Barquera, B. 2006. Membrane topology mapping of the Na⁺-pumping NADH:quinone oxidoreductase from Vibrio cholerae by PhoA/GFP fusion analysis.Journal of Bacteriology. 188:8343-8351.

Barquera, B., Ramirez-Silva, L.,*Morgan, J.E., and Nilges, M.J. 2006. A new flavin radical signal in the Na⁺-pumping NADH:quinone oxidoreductase from Vibrio cholerae: An EPR/ENDOR investigation of the role of the covalently bound flavins in subunits B and C. Journal of Biological Chemistry. 281:36482-36491.

Friedrich, T., Stolpe, S., Schneider, D., Barquera, B., and Hellwig, P. (2005) Ion translocation by the Escherichia coli NADH:ubiquinone oxidoreductase (complex I). Biochem Soc Trans. 33:836-839.

Tziatzios, C., Schubert, D., Schuck, P., Lancaster, C.R.D., Gennis, R.B., and Barquera, B. (2004) The state of association of the Na⁺-translocating reduced nicotinamide adenine dinucleotide:quinone oxidoreductase in detergent solution- an ultracentrifugation study. Progr.Colloid. Polym Sci. 127:48-53. -Barquera, B., Nilges, M. J., Morgan, J.E., Ramirez-Silva, L., Zhou, W., and Gennis, R.B. (2004) Mutagenesis study of the 2Fe-2S center and the FAD binding site of the  Na⁺-translocating NADH:ubiquinone oxidoreductase from Vibrio cholerae. Biochemistry. 43: 12322 -12330.

Barquera, B., Morgan, J.E., Lukoyanov, D., Scholes, C.P., Gennis, R.B., and Nilges, M.J. (2003). X- and W-band EPR and Q-band ENDOR studies of the flavin radical in the Na⁺-translocating NADH:quinone oxidoreductase from Vibrio cholerae. Journal of American Chemical Society. 125: 265-275.