Dax Fu

Brookhaven National Laboratory
Bldg. 463 - P.O. Box 5000
Upton, NY 11973-5000

Research Interests

The challenge:  Recent advances in our understanding of zinc biology have placed this once obscure metal in the center stage, rivaling the biological importance of calcium. Zinc transporters utilize the transmembrane electrochemical potential to move zinc ions across the membrane barrier. Our biochemical studies have shown that the binding affinity of a zinc transporter is much lower than expected for effective Zn(II) equilibrium binding in vivo, while the timescale of Zn(II) transport is millisecond, vastly faster than most metalloproteins that typically take hours or even days to release bound Zn(II). It is not clear how this remarkable thermodynamic-kinetic capacity is built into zinc transporter structures, which support Zn(II) acquisition against steep thermodynamic gradients, rapid Zn(II) mobility across membranes, and yet extraordinary Zn(II)-selectivity over similar divalent cations several orders of magnitude more abundant in vivo.

The goal:   We seek to understand chemical principles governing selective binding and energized movement of zinc ions in membrane transporters. Our fundamental research will facilitate drug discovery efforts targeting human zinc transporters. The human zinc transporter-8 (ZnT-8 or SLC308A) is exclusively expressed in insulin-producing beta-cells, where its activity is required for insulin packing and secretion. ZnT-8 is a major risk factor for type-2 diabetes, an obesity-related disease that is expected to affect 30% of the American population born in 2000. The druggability of ZnT-8 has been established recently. We have filed a patent application on homology modeling of ZnT-8 and its virtual docking of potential drugs.

The approaches:  We have used stopped-flow fluorometry to show how Zn(II) binding to a metal transporter triggers transmembrane movements of bound Zn(II) (8). Binding competition analysis has confirmed that the active binding site is indeed highly selective for Zn(II) over similar divalent cations (5). The Zn(II) binding reaction has been studied directly by titration calorimetry (7), and coordination residues have been identified by mutation-function analysis (3). The transporter structure has been characterized by light-scattering photometry (6), and determined in atomic detail by x-ray crystallography (1). Zinc binding sites revealed in the crystal structure provide insights into the mechanism of Zn(II) binding and transport. Another complementary ongoing study is to understand the structural basis of substrate selectivity in the membrane channel of aquaporins. We have determined the crystal structure of a glycerol-conducting channel GlpF (9), and a homologous water-conducting channel AqpZ (4). The structural mechanism of water/glycerol selectivity has been reviewed recently (2).

The structures of GlpF and YiiP have been solved by MIR/AS/AD phasing at 2.2 and 3.8 Å resolution respectively, while AqpZ was solved by molecular replacement at 3.2 Å resolution.

Selected Publications

• Lu M. and Fu D.
  Structure of the zinc transport YiiP.
  Science, 317:1746-8 (2007).  PubMed  Full Text
  See also: Science Perspective by DH Nies: Science 317:1695-1696 (2007).
• Fu D. and Lu M.
  The structural basis of water permeation and proton exclusion in aquaporins (Review).
  Mol Membr Biol., 24(5):366-374 (2007).  PubMed  Full Text
• Wei Y. and Fu D.
  Binding and transport of metal ions at the dimer interface of the Escherichia coli metal transporter YiiP.
  J Biol Chem., 281(33):23492-23502 (2006).  PubMed  Full Text
• Jiang J., Daniels B.V. and Fu D.
  Crystal structure of AqpZ tetramer reveals two distinct Arg-189 conformations associated with water permeation through the narrowest constriction of the water-conducting channel.
  J Biol Chem., 281(1):454-460 (2006).  PubMed  Full Text  PDB file: 2ABM  Jmol viewer
• Wei Y. and Fu D.
  Selective metal binding to a membrane-embedded aspartate in the Escherichia coli metal transporter YiiP (FieF).
  J Biol Chem., 280(40):33716-33724 (2005).  PubMed  Full Text
• Wei Y., Li H. and Fu D.
  Oligomeric state of the Escherichia coli metal transporter YiiP.
  J Biol Chem., 279(38):39251-39259 (2004).  PubMed  Full Text
• Chao Y. and Fu D.
  Thermodynamic studies of the mechanism of metal binding to the Escherichia coli zinc transporter YiiP.
  J Biol Chem., 279(17):17173-17180(2004).  PubMed  Full Text
• Chao Y and Fu D.
  Kinetic study of the antiport mechanism of an Escherichia coli zinc transporter, ZitB.
  J Biol Chem., 279(13):12043-12050 (2004).  PubMed  Full Text 
• Fu D., Libson A., Miercke L.J., Weitzman C., Nollert P., Krucinski J. and Stroud R.M.
  Structure of a glycerol-conducting channel and the basis for its selectivity.
  Science, 290:481-486 (2000).  PubMed  Full Text  PDB file: 1FX8  Jmol viewer

Last Modified: October 22, 2009
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One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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