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Details of Grant 

EPSRC Reference: EP/J015318/1
Title: Electron transfer in engineered single protein molecules
Principal Investigator: Elliott, Dr M
Other Investigators:
Macdonald, Professor JE Jones, Professor D
Researcher Co-Investigators:
Project Partners:
Science Made Simple Ltd Technical University of Denmark University of Exeter
Department: School of Physics and Astronomy
Organisation: Cardiff University
Scheme: Standard Research
Starts: 01 October 2012 Ends: 31 March 2016 Value (£): 455,618
EPSRC Research Topic Classifications:
Materials Characterisation Surfaces & Interfaces
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
18 Apr 2012 EPSRC Physical Sciences Materials - April Announced
Summary on Grant Application Form
All living organisms contain proteins - nanoscale molecular machines which have a myriad of functions. A large fraction of these proteins are "electron transfer" proteins which, as the name suggests, are capable of moving electrical charge from one place to another - either within the protein or between proteins. Such proteins are absolutely essential to the physics of life, controlling biological processes as varied as respiration, photosynthesis and the creation of organic molecules from basic elements (hydrogen, carbon, nitrogen, oxygen, etc.).

Although they actually function at essentially the single molecule level, most of our understanding of electron transfer (ET) proteins comes from experiments performed on large assemblies of protein molecules, not individual molecules. This is perhaps not surprising since it is usually difficult to locate a single molecule, or to obtain a measurable signal from just one molecule. Many traditional measurements therefore look at the optical properties of an assembly of molecules in solution. Others measure the electrical properties of metal surfaces covered in a layer of molecules.

The aim of our project is to develop a new way to measure individual ET protein molecules, and use these measurements to gain a better understanding of the ET process (directly relevant to theorists and a prerequisite for any biolectronic applications). To do this we first make two electrical contacts to the protein, and then incorporate it as part of an electrical circuit. By measuring how easy it is to pass current through the circuit, we can examine just how the protein functions to transfer electrons. We can also change other properties of the protein (such as a metal centre which is common in ET proteins) to examine their role in the ET process.

The first problem is how to make a reliable electrical contact to a single molecule. Fortunately, the methods already developed in protein engineering allow this to be done: it is possible to modify the protein surface to introduce specific chemical groups which strongly attach the molecule to a metal surface. This is achieved by altering the genetic material encoding the protein, so that the required chemical groups can be placed at precisely known positions in the protein. Multiple identical copies of the modified protein are produced in this way.

The second problem is how to examine just a single molecule. This has become possible over the past few years following the invention of the scanning tunnelling microscope or STM. This instrument allows an almost atomically-sharp metal tip to be brought close to a (sufficiently flat) metal surface; if the distance between tip and surface is small enough (around one nanometre - a millionth of a millimetre - or so) electrons in the tip can pass to the surface when a voltage is applied between them. The tip and surface don't have to touch, but the electrons pass because of the quantum mechanical "tunnelling" effect. By scanning the tip across the metal surface under computer control, it is possible to measure exactly how flat the surface is, and even form an image of individual metal atoms. If our protein molecules are sprinkled on the surface, it is possible to use the STM to see exactly where they have adhered, and to put the tip in contact with them. This completes our electrical circuit.

Measuring electron transfer through proteins in this way has not previously been done, and lets us explore the protein with a high degree of control. But it is not interesting simply for its own sake - it means we can better understand just how ET proteins operate at the level of a single molecule. Also, development of bioelectronic components using ET proteins, which is a subject of rapidly growing interest, ultimately depends on our ability to study them at the single molecule level and with electrical contacts.

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