Article

A 3D structure model of the melibiose permease of Escherichia coli represents a distinctive fold for Na+ symporters

Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 09/2009; 106(36):15291-6. DOI: 10.1073/pnas.0905516106
Source: PubMed

ABSTRACT The melibiose permease of Escherichia coli (MelB) catalyzes the coupled stoichiometric symport of a galactoside with a cation (either Na(+), Li(+), or H(+)), using free energy from the downhill translocation of one cosubstrate to catalyze the accumulation of the other. Here, we present a 3D structure model of MelB threaded through a crystal structure of the lactose permease of E. coli (LacY), manually adjusted, and energetically minimized. The model contains 442 consecutive residues ( approximately 94% of the polypeptide), including all 12 transmembrane helices and connecting loops, with no steric clashes and superimposes well with the template structure. The electrostatic surface potential calculated from the model is typical for a membrane protein and exhibits a characteristic ring of positive charges around the periphery of the cytoplasmic side. The 3D model indicates that MelB consists of two pseudosymmetrical 6-helix bundles lining an internal hydrophilic cavity, which faces the cytoplasmic side of the membrane. Both sugar and cation binding sites are proposed to lie within the internal cavity. The model is consistent with numerous previous mutational, biochemical/biophysical characterizations as well as low-resolution structural data. Thus, an alternating access mechanism with sequential binding is discussed. The proposed overall fold of MelB is different from the available crystal structures of other Na(+)-coupled transporters, suggesting a distinctive fold for Na(+) symporters.

Download full-text

Full-text

Available from: Lan Guan, Aug 29, 2015
0 Followers
 · 
127 Views
  • Source
    • "The proximity of Gly117 to the binding site of the cation is suggested by the observation that in the double mutant D55S/G117D, a carboxyl group at position 117 can partially compensate for the loss of the carboxyl group at position 55 [31]. This result indicated that in the 3- dimensional structure of the protein position 117 in helix IV is close to position 55 in helix II in agreement with the structural model [15]. Furthermore, helix IV seems to have a role in connecting the sugar and cation binding sites [24]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Replacement of the glycine at position 117 by a cysteine in the melibiose permease creates an interesting phenotype: while the mutant transporter shows still transport activity comparable to the wild type its pre steady-state kinetic properties are drastically altered. The transient charge displacements after substrate concentration jumps are strongly reduced and the fluorescence changes disappear. Together with its maintained transport activity this indicates that substrate translocation in G117C melibiose permease is not impaired but that the initial conformation of the mutant transporter differs from that of the wild type permease. A kinetic model for the G117C melibiose permease based on a rapid dynamic equilibrium of the substrate free transporter is proposed. Implications of the kinetic model for the transport mechanism of the wild type permease are discussed.
    Biochimica et Biophysica Acta 10/2011; 1808(10):2508-16. DOI:10.1016/j.bbamem.2011.07.017 · 4.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The procedure of the Pt/(CeO2–TiO2) catalyst preparation is crucial for the microstructure and catalytic properties in CO oxidation. Impregnation of ceria doped TiO2 with platinum nitrate solution followed heating in air at 500°C leads to the formation of ultra fine platinum particles 0.5–0.6nm in size stabilized at interblock boundaries of the support formed by irregularly intergrown anatase particles. Calcination of the catalyst in hydrogen at 250°C leads to the formation of the platinum particles with 2–5nm in size. The catalyst containing ultra fine platinum particles is much more active than the catalyst with particles of 2–5nm in size. Infrared spectra of CO adsorbed on Pt revealed that high CO oxidation activity is exhibited by ultra fine Pt particles due to the high concentration of weakly bonded Pt0-CO complexes.
    Studies in surface science and catalysis 01/2010; 175:369-372. DOI:10.1016/S0167-2991(10)75062-X
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: All cells must traffic proteins into and across their membranes. In bacteria, several pathways have evolved to enable protein transfer across the inner membrane, the periplasm, and the outer membrane. The major route of protein translocation in and across the cytoplasmic membrane is the general secretion pathway (Sec-pathway). The biogenesis of membrane proteins not only requires protein translocation but also coordinated targeting to the membrane beforehand and folding and assembly into their protein complexes afterwards to function properly in the cell. All these processes are responsible for the biogenesis of membrane proteins that mediate essential functions of the cell such as selective transport, energy conversion, cell division, extracellular signal sensing, and motility. This review will highlight the most recent developments on the structure and function of bacterial membrane proteins, focusing on the journey that integral membrane proteins take to find their final destination in the inner membrane.
    Cellular and Molecular Life Sciences CMLS 03/2010; 67(14):2343-62. DOI:10.1007/s00018-010-0303-0 · 5.86 Impact Factor
Show more