Chemistry and Biological Chemistry Department
Education and Training
Ph.D. National University of Mexico
Postdoctoral Training: University of Illinois at Urbana-Champaign, University of Helsinki.
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
Sodium bioenergetics in pathogenic bacteria. Mechanistic enzymology of respiratory proteins and ion transporters. Membrane proteins. Bacterial physiology.
Ion gradients are important throughout all biology. In many pathogenic bacteria, essential functions such as energy production, homeostasis, adaptation to different environments and important mechanisms of antibiotic resistance, all rely on transport of Na+ across the cell membrane. Thus, sodium metabolism is a key to understanding how pathogens proliferate and spread disease.
The research in my laboratory focuses on Na+ metabolism: from the mechanistic enzymology of proteins that generate sodium gradients to the physiological of role of the processes driven by this gradient.
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 Pseudomonas aeruginosa. 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 Pseudomonas aeruginosa: 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 Pseudomonas aeruginosa 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.
Neehaul, Y., Juarez, O., Barquera, B. Hellwig, P. 2013. Infrared spectroscopy evidence of a redox-dependent conformational change involving in binding residue NqrB-D397 in the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. Biochemistry. 52:3085-30-93.
Juárez O, Neehaul Y, Turk E, Chahboun N, Demicco JM, Hellwig P, Barquera B. 2012. The Role of Glycine Residues 140 and 141 of Subunit B in the Functional Ubiquinone Binding Site of the Na+-pumping NADH:quinone Oxidoreductase from Vibrio cholerae. J Biol Chem. 287:25678-85.
Neehaul Y, Juárez O, Barquera B, Hellwig P. 2012. Thermodynamic contribution to the regulation of electron transfer in the Na(+)-pumping NADH:quinone oxidoreductase from Vibrio cholerae. Biochemistry. 51:4072-4077.
Juárez O, Barquera B. 2012. Insights into the mechanism of electron transfer and sodium translocation of the Na(+)-pumping NADH:quinone oxidoreductase. Biochim Biophys Acta. 1817:1823-32.
Juárez, O., Shea, M.E., Makhatadze, G.I., and Barquera, B. 2011. The Role and Specificity of the Catalytic and Regulatory Cation-binding Sites of the Na+-pumping NADH:Quinone Oxidoreductase from Vibrio cholerae. J. Biol. Chem. 286: 26383-26390.
Juárez, O., Morgan, J.E., Nilges, M.J. and Barquera, B. 2010. Energy transducing redox steps of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. PNAS 107:12505-12510.
Juárez, O., Athearn, K., Gillespie, P., Barquera, B. 2009. Acid residues in the transmembrane helices of the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae involved in sodium translocation. Biochemistry 48:9516-9524.
Juárez, O., Morgan, J.E., and Barquera, B. 2009. The electron transfer pathway of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. J Biol Chem 284: 8963ˆ8972.
Juárez, O., Nilges, M. J., Gillespie, P., Cotton, J., and Barquera, B. 2008. Riboflavin is an active redox cofactor in the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae. J Biol Chem 283:33162-33167.
Backiel, J., Juarez, O., Zagorevski, D. V., Wang, Z., Nilges, M. J., Barquera, B. (2008). "Covalent Binding of Flavins to RnfG and RnfD in the Rnf Complex from Vibrio cholerae." Biochemistry 47(43): 11273-84.
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.