Center for Membrane Biology
Department of Biochemistry and Molecular Biology
Program in Biochemistry and Molecular Biology
University of Texas-Houston Medical School
P.O. Box 20708 - Houston, Texas 77225
Tel: 713-500-6083 Fax: 713-500-0545
Ph.D, University of Berne, Switzerland
Postdoctoral Fellow, Paul Scherrer Institute, Villigen, Switzerland
Structural biology of membrane proteins
Maintaining ion homeostasis across the cell membrane is fundamental to normal cell function. The research of our lab focuses on structure, function and regulation of ion transport proteins by using a combination of biochemical and biophysical approaches, primarily X-ray crystallography.
Ammonium transport proteins
Ammonium ubiquitously exists in biological fluids. In bacteria, ammonium movement across the cell membrane is a dynamic process synchronized with global nitrogen metabolism. Recently our high resolution crystal structures of the ammonium transport protein AmtB from E.coli (see figure) have shed light on the mechanism of ammonium conduction, in which a pair of histidine residues in the hydrophobic pore is suggested to play a critical role in substrate selectivity and permeation. However, in eukaryotic systems, the members of the ammonium transport protein family, the Rhesus proteins, have diversified functions. In red blood cells, these Rh blood antigens appear to serve as primary components in a giant CO2 metabolon on the cell membrane and are believed to facilitate CO2/O2 exchange in blood; while in kidney, Rhesus proteins have been suggested to act as ammonium carriers to prevent fluid acidosis. The major focus of my lab is to study the functional and structural features conferring substrate specificity to this protein family and their mechanisms of permease activity by using biochemical and structural biology approaches.
Calcium ion, the most abundant cation in the human body, serves as a universal secondary messenger to modulate a broad array of biological processes from cardiac contraction to neuronal transmission. Calcium/sodium exchanger proteins extrude calcium ions by trading them for sodium ions imported into the cytosol, an important step in calcium signaling pathways. In cardiac myocytes, dysfunction of this protein prevents the relaxation step in each cardiac cycle. Conversely, overexpression of this molecule in vascular membranes results in salt-dependent hypertension. Calcium ion homeostasis through the calcium/sodium exchanger is fine-tuned in the sub-micromolar range with a sophisticated self-regulation mechanism on its cytosolic surface. Our interest is to understand how this protein selects calcium and sodium ions oppositely and then mediates their exchange across the channel, as well as its self-regulation mechanism. Our ongoing structural investigation should greatly accelerate the understanding of calcium signaling processes.
Permeation of an ammonium ion through a trimeric AmtB protein on the inner membrane.
Javelle, A., Lupo, D., Zheng, L., Li, X.-D., Winkler, F.K., Merrick, M. (2006) An unusual twin-His arrangement in the pore of ammonia channels is essential for substrate conductance. J Biol Chem. 2006 Oct 12.
Li X.D., Lupo D., Zheng L., Winkler F. (2006) Structural and functional insights into the AmtB/Mep/Rh protein family. Transfus Clin Biol. 13(1-2):65-9.
Zheng L., Manetsch R., Woggon W.-R., Baumann U., Reymond J.-L. (2005) Mechanistic study of proton transfer in catalytic antibody 16E7 by site-directed mutagenesis and homology modeling. Bioorg Med Chem. 13(4):1021-9.
Zheng, L., Kostrewa, D., Berneche, S., Winkler, F.K. and Li X.-D. (2004) The mechanism of ammonia transport based on the crystal structure of AmtB of E.coli. Proc Natl Acad Sci U S A. 101(49):17090-95.
Zheng, L., Baumann, U., Reymond, J.-L. (2004) Molecular mechanism of enantioselective proton transfer to carbon in catalytic antibody 14D9. Proc Natl Acad Sci U S A. 101(10):3387-92.
Zheng, L., Baumann U., Reymond J.-L. (2004) An efficient one-step site-directed and site-saturation mutagenesis protocol. Nucleic Acids Res. 32(14):e115.
Zheng L., Goddard J.-P., Baumann U., Reymond J.-L. (2004) Expression improvement and mechanistic study of the retro-diels-alderase catalytic antibody 10F11 by site-directed mutagenesis. J Mol Biol. 341(3):807-14.
Manetsch R., Zheng L., Reymond M.T., Woggon W.D., Reymond J.-L. (2004) A catalytic antibody against a tocopherol cyclase inhibitor. Chemistry. 10(10):2487-2506.
Zheng L., Baumann U., Reymond J.-L. (2003) Production of a functional catalytic antibody ScFv-NusA fusion protein in bacterial cytoplasm. J Biochem. (Tokyo) 133(5):577-81.