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Published Online October 16, 2008
Science DOI: 10.1126/science.1164440

Research Articles

Submitted on August 8, 2008
Accepted on September 26, 2008

Structure and Molecular Mechanism of a Nucleobase-Cation-Symport-1 Family Transporter

Simone Weyand 1{dagger}, Tatsuro Shimamura 2{dagger}, Shunsuke Yajima 3*, Shun’ichi Suzuki 4*, Osman Mirza 5*, Kuakarun Krusong 6, Elisabeth P. Carpenter 7, Nicholas G. Rutherford 8, Jonathan M. Hadden 8, John O’Reilly 8, Pikyee Ma 8, Massoud Saidijam 9, Simon G. Patching 8, Ryan J. Hope 8, Halina T. Norbertczak 8, Peter C. J. Roach 8, So Iwata 10*, Peter J. F. Henderson 8*, Alexander D. Cameron 1

1 Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0DE, UK.; Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Human Receptor Crystallography Project, ERATO, Japan Science and Technology Agency, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
2 Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Human Receptor Crystallography Project, ERATO, Japan Science and Technology Agency, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.; Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-Ku, Kyoto 606-8501, Japan.
3 Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Human Receptor Crystallography Project, ERATO, Japan Science and Technology Agency, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.; Present address: Department of Bioscience, Tokyo University of Agriculture, Sakuragaoka 1-1-1, Setagaya-ku, Tokyo 156-8502, Japan
4 Astbury Centre for Structural Molecular Biology, Institute for Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK.; Present address: Aminosciences Laboratories, Ajinomoto Co. Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa 210-8681, Japan.
5 Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Present address: Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100, Denmark.
6 Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Present address: Department of Biochemistry, Faculty of Science, Chulalongkorn University, Phyathai Road, Patumwan, Bangkok 10330, Thailand.
7 Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0DE, UK.; Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.
8 Astbury Centre for Structural Molecular Biology, Institute for Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK.
9 Astbury Centre for Structural Molecular Biology, Institute for Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK.; School of Medicine, Hamedan University of Medical Sciences, Hamedan, Iran.
10 Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0DE, UK.; Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.; Human Receptor Crystallography Project, ERATO, Japan Science and Technology Agency, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.; Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-Ku, Kyoto 606-8501, Japan.; Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho Tsurumi-ku, Yokohama 230-0045 Japan.

* To whom correspondence should be addressed.
So Iwata , E-mail: s.iwata{at}imperial.ac.uk
Peter J. F. Henderson , E-mail: p.j.f.henderson{at}leeds.ac.uk

{dagger}These authors contributed equally to this work.

The ‘Nucleobase-Cation-Symport-1’, NCS1, transporters are essential components of salvage pathways for nucleobases and related metabolites. Here, we report the 2.85 Å resolution structure of the NCS1 benzyl-hydantoin transporter, Mhp1, from Microbacterium liquefaciens. Mhp1 contains 12 transmembrane helices, 10 of which are arranged in two inverted repeats of 5 helices. The structures of the outward-facing open and substrate-bound occluded conformations were solved, showing how the outward-facing cavity closes upon binding of substrate. Comparisons with the leucine (LeuTAa) and the galactose (vSGLT) transporters reveal that the outward- and inward-facing cavities are symmetrically arranged on opposite sides of the membrane. The reciprocal opening and closing of these cavities is synchronised by the inverted repeat helices 3 and 8, providing the structural basis of the ‘alternating access’ model for membrane transport.


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