Border control: study shows how proteins permit entry to a cell

The means by which proteins provide a ‘border control’ service, allowing cells to take up chemicals and substances from their surroundings, whilst keeping others out, is revealed in unprecedented molecular detail for the first time today (16 October) in Science Express.

The scientists behind the new study have visualised the structure of a protein called Microbacterium hydantoin permease, or ‘Mph1’, which lives in the oily membrane that surrounds bacteria cells. It belongs to a group of proteins known as ‘transporters’ which help cells take up certain substances from the environment around them. This is the first time scientists have been able to show how a transporter protein opens and closes to allow molecules across the membrane and into the cell by accurate analysis of its molecular structure in different states.

Professor So Iwata from Imperial College London’s Department of Life Sciences, one of the authors of the new study, explains that solving the structure of the Mph1 bacterial transporter protein is very important because hundreds of similar transporters are found in the membranes of human cells:

"Transporter proteins play an important role in the human body – they are responsible for letting different substances, including salts, sugars and amino acids, into our cells and are targets for a large number of drugs. Understanding the details of how this transport mechanism works may help researchers to design new, more effective, drugs in the future."

Part of the protein structure

The group’s research into this protein began in 2000 with a joint project with the Ajinomoto Company from Japan. This company work with a bacterium called Microbacterium liquefaciens which has the Mph1 protein in its cell membranes. The project revealed that Mph1 helps the uptake of amino acid-like molecules called hydantoins across the otherwise impermeable cell membrane.

Professor Peter Henderson from the University of Leeds, co-author of the study, adds: "The major problem was to produce enough protein for the structural studies. We developed methods for the amplified expression of the Mhp1 protein in a genetically-engineered host organism, Escherichia coli, and procedures for the subsequent efficient purification of the protein from the cell membranes. We could then maintain a ‘pipeline’ to supply an exceptional amount of the membranes containing the excess Mhp1 protein to our colleagues at Imperial".

Professor Iwata and his colleagues analysed the structure of Mph1 using the facilities at the Membrane Protein Laboratory (MPL), which is an Imperial College outstation at the Diamond Light Source national synchrotron facility in Oxfordshire. They used the MPL, which is a dedicated facility for membrane protein structural studies, to build an accurate picture of the Mph1 protein binding to hydantoin.

The researchers analysed the structure of Mph1 before and after it had taken in a hydantoin molecule from outside the cell, and also used the structure of a related transporter, vSGLT, for insight into the latter stages of the take-up process. These three structures revealed new molecular-level detail of how Mhp1 transports a hydantoin molecule across the cell membrane.

The researchers saw that the Mph1 protein opens up on its outer-facing side, allowing the hydantoin molecule to move inside. Once the hydantoin is bound, the ‘door’ to the outside world closes behind it, ensuring that no other substances have been let in. Then the gate on the inward-facing side opens to release the hydantoin into the cell.

Professor Iwata comments on the significance of the discovery, saying: "Our research has revealed the detailed molecular function of an important membrane protein. We now know how the protein facilitates the movement hydantoin across the cell membrane without letting any other substances through at the same time. This mechanism is likely to be shared by many of cell membrane proteins, including those in the human body, so this is an important step forward in our understanding of the fundamental processes which occur in our cells."

Professor Iwata leads an international team of scientists at the Membrane Protein Laboratory (MPL) at the Diamond Light Source. The MPL is a joint venture between Imperial College London and Diamond Light Source, with funding from the Wellcome Trust and the Japan Science and Technology Agency.

Professor Henderson is Scientific Director of the EU-funded European Membrane Protein consortium, ‘EMeP’, which promotes collaborative research on membrane proteins between 18 European Institutions.

The Science Express research out today was carried out by researchers from Imperial College and the University of Leeds in the UK, in collaboration with scientists from Japan and Iran. The work was funded in the UK by the BBSRC, the Japan Science and Technology Agency, the EU, the Wellcome Trust and Ajinomoto Co.

 -Ends-

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Danielle Reeves, Imperial College London press office
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Notes to Editors:

 1. The structural data used in the paper was gathered at the European Synchrotron Radiation Facility (ESRF) in Grenoble and the Swiss Light Source.

 2. ‘Structure and molecular mechanism of a nucleobase-cation symport-1 family transporter’ Science Express, Thursday 16 October 2008. Simone Weyand (1, 2, 3) Tatsuro Shimamura (2, 3, 4) Shunsuke Yajima (2, 3) Shunichi Suzuki (5), Osman Mirza (2), Kuakarun Krusong (2), Elisabeth P. Carpenter (1, 2), Nicholas G. Rutherford (5), Jonathan M. Hadden (5), John O’Reilly (5), Pikyee Ma (5), Massoud Saidijam (5, 6), Simon G. Patching (5), Ryan J. Hope (5), Halina T. Norbertczak (5), Peter C.J. Roach (5), So Iwata (1,2,3,4,7), Peter J. F. Henderson (5) and Alexander D. Cameron (1,2,3).

 (1) Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0DE, UK.

(2) Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College, London SW7 2AZ, UK.

(3) Human Receptor Crystallography Project, ERATO, Japan Science and Technology Agency, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.

(4) Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-Ku, Kyoto 606-8501, Japan.

(5). Astbury Centre for Structural Molecular Biology, Institute for Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK.

(6) School of Medicine, Hamedan University of Medical Sciences, Hamedan, Iran

(7) Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho Tsurumi-ku, Yokohama 230-0045 Japan

 3. About Diamond Light Source

Diamond generates extremely intense pin-point beams of synchrotron light of exceptional quality ranging from x-rays, ultra-violet and infrared. For example Diamond’s x-rays are around 100 billion times brighter than a standard hospital X-ray machine or 10 billion times brighter than the sun.

Many of our everyday commodities that we take for granted, from food manufacturing to cosmetics, from revolutionary drugs to surgical tools, from computers to mobile phones, have all been developed or improved using synchrotron light.

·         Diamond will bring benefits to:

•  Biology and medicine. For example, the fight against illnesses such as Parkinson's, Alzheimer's, osteoporosis and many cancers will benefit from the new research techniques available at Diamond.

 

 The physical and chemical sciences. For example, in the near future, engineers will be able to image their structure down to an atomic scale, helping them to understand the way impurities and defects behave and how they can be controlled.

• The Environmental and Earth sciences. For example, Diamond will help researchers to identify organisms that target specific types of contaminant in the environment which can potentially lead to identifying cheap and effective ways for cleaning polluted land.
• 4. About Imperial College London

Imperial College London - rated the world’s fifth best university in the 2007 Times Higher Education Supplement University Rankings - is a science-based institution with a reputation for excellence in teaching and research that attracts 12,000 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Website: www.imperial.ac.uk

5. The University of Leeds is one of the largest higher education institutions in the UK with more than 30,000 students from 130 countries. With a turnover of £450m, Leeds is one of the top ten research universities in the UK, and a member of the Russell Group of research-intensive universities.