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UK team reveals all three structures of single transporter protein

UK team reveals all three structures of single transporter protein

A team of researchers from the Universities of Leeds, Oxford and Imperial College London have captured the 3D atomic models of a single transporter protein in each of its three main structural states.

An achievement that has been a goal of researchers from around the world for over 25 years.   

The discovery offers remarkable insight into the function of one of the body's most fundamental processes - the movement of essential chemicals into cells of the body - and creates the opportunity to develop brand new drugs.

Biologists have surmised that transporter proteins of this type, which sit in the cell membrane, carry molecules through the otherwise impermeable membrane by shifting between at least three distinct structural states, controlled by ion gradients.

In the first state, there is an outward-facing cavity. A compound will enter this cavity and attach to a binding site whereupon the protein will move to a second state with the cargo locked inside. The third state is formed when the protein opens up a cavity on the inward-facing side to release the compound into the cell.  The switch between outward and inward-facing sides works rather like a 'kissing gate' in which the cavity is either on one side or the other but there is never a direct channel through the protein.

However, until now, scientists had never observed the structural details of these three states in a single protein and theories about how the mechanism worked in detail were based on stitching together their observations from different transporters.

"Previous models gave us a broad understanding of the mechanism involved, but this could never really be usefully applied for drug development," says Professor Peter Henderson of the University of Leeds. "The goal for researchers in this area has always been to observe the entire mechanism in a single protein."

The research, published today in Science, reports the mapping of the inward-facing structure of the bacterial Mhp1 transporter protein, the third structural state that they have determined for this protein.  The team has been studying Mhp1 for more than ten years and their observations of the first two structures were published in Science in October 2008.

The protein was produced in Leeds; the structures were determined by X-ray crystallography and analysed at Imperial College and the Imperial College Membrane Protein Laboratory (MPL) located at Diamond Light Source. To further investigate the transitions between the three states of the protein dynamic molecular simulations were carried out at Oxford University.  

"This third structure completes the picture and we can now understand Mhp1's 'alternating access' mechanism in great detail," said Dr Alexander Cameron, from the Division of Molecular Biosciences at Imperial College London. "We also unexpectedly found that the structures are similar across many transporter proteins previously thought to be different, so we're expecting our model to help achieve some rapid progress in the research of colleagues around the world."

The detailed knowledge of the mechanism could unlock new drug developments in several ways, says Professor Henderson. "Altering the delivery of compounds into a cell is one potential benefit for treating illness. For example this could be useful in treating conditions where certain chemicals are lacking and need boosting permanently - such as serotonin for those suffering from depression and glucose for those with diabetes."

The mechanism's detail is already being used by chemists in the EU-funded European Drug Initiative on Channels and Transporters consortium (EDICT), which Professor Henderson leads. "We've found around 20 compounds that match Mhp1's binding site, and of these, three have been shown to bind. I think we are entering an exciting period of discovery." 

"It's taken a long time to get to this point - over ten years - but then difficult science takes time.  This is the point at which blue skies research evolves into useful applications," says Professor Henderson. "It's the best thing I've been involved in during my academic career."

Funded by the Biotechnology and Biological Sciences Research Council (BBSRC), the EU, the Japanese Science and Technology Agency and the Wellcome Trust, the research team comprises: Professor Henderson and colleagues from Leeds, who expressed and purified the Mhp1 protein; Professor So Iwata, Dr Alex Cameron and colleagues from Imperial College London and the MPL who imaged the crystals and combined all the information to propose a mechanism for the alternating access model; and Professor Mark Sansom and Dr Oliver Beckstein from the University of Oxford who authenticated the plausibility of the transitions between the three states.

Professor Henderson says that the next step is to investigate what triggers the protein to change between the states and the team has secured further funding from BBSRC and the EDICT consortium to pursue this.

For further information:

Please contact the University of Leeds Press Office on +44 (0)113 343 4031 or email pressoffice@leeds.ac.uk

Lucy Goodchild, Imperial College London press office: Tel +44 (0)20 7594 6702 or email lucy.goodchild@imperial.ac.uk

Notes to editors

  1. The paper, Molecular Basis of Alternating Access Membrane Transport by the Sodium-Hydantoin Transporter Mhp1 is published in Science, on Friday, 23 April 2010. A copy of the embargoed paper is available on request from the AAAS Office of Public Programs. Please contact the press team on +1-202-326-6440 or scipak@aaas.org
  2. Transporter proteins are notoriously difficult to work with as they denature in water, so their purification and crystallisation is fraught with technical challenges. Even when crystals of the protein are successfully produced at good enough resolution to image, deduction of the structure can take months to process. There are probably thousands of different transporter proteins in the human body.
  3. The function of Mhp1 (Microbacterium hydantoin permease) is to transport the molecules called hydantoins into cells, where they are converted into useful amino acids. These amino acids are commercially important as they are used to make several food and drink supplements and are potentially feedstocks for pharmaceutical drugs. The function of Mhp1 was initially discovered at Leeds in 2000, during a two year visit to Leeds by Japanese researcher, Dr Shun'ichi Suzuki, from Ajinomoto Inc. This earlier work was patented in Japan and the USA.
  4. Peter Henderson is Professor of Biochemistry and Molecular Biology at the Astbury Centre for Structural Molecular Biology in the Faculty of Biological Sciences, University of Leeds (http://www.astbury.leeds.ac.uk/).  He also co-ordinates the European Drug Initiative for Transporters and Channels (EDICT), involving 27 academic and industrial partners in 12 countries led by the University of Leeds (http://www.edict-project.eu/). 
  5. The Faculty of Biological Sciences at the University of Leeds is one of the largest in the UK, with over 150 academic staff and over 400 postdoctoral fellows and postgraduate students. The Faculty is ranked 4th in the UK (Nature Journal, 457 (2009) doi :10.1038/457013a) based on results of the 2008 Research Assessment Exercise (RAE). The RAE feedback noted that "virtually all outputs were assessed as being recognized internationally, with many (60%) being internationally excellent or world-leading" in quality. The Faculty's research grant portfolio totals some £60M and funders include charities, research councils, the European Union and industry. http://www.fbs.leeds.ac.uk/
  6. Professor So Iwata leads an international team of scientists including Dr Alex Cameron in the Membrane Protein Laboratory (MPL) at the Diamond Light Source in Oxfordshire. 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.
  7. About Imperial College London
    Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 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. Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve health in the UK and globally, tackle climate change and develop clean and sustainable sources of energy. http://www.imperial.ac.uk/
  8. Professor Mark Sansom leads the Structural Bioinformatics and Computational Biochemistry Unit specializing in membrane proteins at the University of Oxford. His colleague, Dr Oliver Beckstein, is a Research Fellow there funded by EDICT.  http://sbcb.bioch.ox.ac.uk/
  9. Oxford University's Medical Sciences Division is one of the largest biomedical research centres in Europe. It represents almost one-third of Oxford University's income and expenditure, and two-thirds of its external research income. Oxford's world-renowned global health programme is a leader in the fight against infectious diseases (such as malaria, HIV/AIDS, tuberculosis and avian flu) and other prevalent diseases (such as cancer, stroke, heart disease and diabetes). Key to its success is a long-standing network of dedicated Wellcome Trust-funded research units in Asia (Thailand, Laos and Vietnam) and Kenya, and work at the MRC Unit in The Gambia. Long-term studies of patients around the world are supported by basic science at Oxford and have led to many exciting developments, including potential vaccines for tuberculosis, malaria and HIV, which are in clinical trials.
  10. The Biotechnology and Biological Sciences Research Council (BBSRC)
    BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £450 million in a wide range of research that makes a significant contribution to the quality of life in the UK and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors. http://www.bbsrc.ac.uk%20/

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