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Structure-based mechanism for Na+/melibiose symport by MelB

Author

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  • Abdul S. Ethayathulla

    (Center for Membrane Protein Research, Texas Tech University Health Sciences Center)

  • Mohammad S. Yousef

    (Center for Membrane Protein Research, Texas Tech University Health Sciences Center
    Present address: Department of Physics, College of Arts and Sciences, Southern Illinois University, Edwardsville, Illinois 62026-1654, USA (on leave from: Biophysics Department, Faculty of Science, Cairo University, Egypt))

  • Anowarul Amin

    (Center for Membrane Protein Research, Texas Tech University Health Sciences Center)

  • Gérard Leblanc

    (University of California
    Present address: CEA-DSV-Fontenay aux Roses, Cross Division of Toxicology, 92 265 Fontenay aux Roses BP 6, France)

  • H. Ronald Kaback

    (University of California)

  • Lan Guan

    (Center for Membrane Protein Research, Texas Tech University Health Sciences Center)

Abstract

The bacterial melibiose permease (MelB) belongs to the glycoside–pentoside–hexuronide:cation symporter family, a part of the major facilitator superfamily (MFS). Structural information regarding glycoside–pentoside–hexuronide:cation symporter family transporters and other Na+-coupled permeases within MFS has been lacking, although a wealth of biochemical and biophysical data are available. Here we present the three-dimensional crystal structures of Salmonella typhimurium MelBSt in two conformations, representing an outward partially occluded and an outward inactive state of MelBSt. MelB adopts a typical MFS fold and contains a previously unidentified cation-binding motif. Three conserved acidic residues form a pyramidal-shaped cation-binding site for Na+, Li+ or H+, which is in close proximity to the sugar-binding site. Both cosubstrate-binding sites are mainly contributed by the residues from the amino-terminal domain. These two structures and the functional data presented here provide mechanistic insights into Na+/melibiose symport. We also postulate a structural foundation for the conformational cycling necessary for transport catalysed by MFS permeases in general.

Suggested Citation

  • Abdul S. Ethayathulla & Mohammad S. Yousef & Anowarul Amin & Gérard Leblanc & H. Ronald Kaback & Lan Guan, 2014. "Structure-based mechanism for Na+/melibiose symport by MelB," Nature Communications, Nature, vol. 5(1), pages 1-11, May.
    • Handle: RePEc:nat:natcom:v:5:y:2014:i:1:d:10.1038_ncomms4009
    DOI: 10.1038/ncomms4009
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    Cited by:

    1. Victoria C. Young & Hanayo Nakanishi & Dylan J. Meyer & Tomohiro Nishizawa & Atsunori Oshima & Pablo Artigas & Kazuhiro Abe, 2022. "Structure and function of H+/K+ pump mutants reveal Na+/K+ pump mechanisms," Nature Communications, Nature, vol. 13(1), pages 1-15, December.

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