Electron transfer in engineered single protein molecules

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.

The impact on academic beneficiaries, including our collaborators, is described under the section "Academic Beneficiaries".

Science Made Simple (SMS) will be a core partner in the development of suitable outreach activity for us. They have a proven track of over eight years of engaging end-users (schools or public event beneficiaries) with contemporary research. They also have wide experience in training researchers in public engagement using a range of innovative formats such as performance skills, science busking and theatre production skills. Through training our research groups, they plan to create a legacy of skills amongst the research team that can be used for years to come as individual careers develop - benefiting especially the PDRA. SMS will also give advice in setting up web pages aimed at benefiting schools and the wider public. These pages will provide advice and offers of talks to schools.

SMS has provided a statement of support describing the benefits of this activity to them, and will also provide around £1.5k of work in kind (marketing and consultancy advice on targeting schools and other audiences, advice for PDRA and engagement events). SMS will benefit especially through the opportunity to work with cutting edge researchers to expand their knowledge around this area, which will benefit their outreach work with students and the public.

Communication by the applicants with the wider community has already been established through numerous talks to schools audiences and scientific societies. Cardiff University runs an open day every year and our research will be showcased in this forum. The School of Physics and Astronomy runs an annual 6th form conference where we shall continue to give presentations of our current research. The local Science Cafe in Cardiff, which any interested members of the local community may attend, will provide a valuable opportunity for public engagement.

One tool used in this project, synthetic biology, has been much debated amongst politicians and the wider public. Policy makers need to know the worth, benefits and pitfalls (including public perception) in order to regulate the area; one of us (DDJ) recently (2009) reported to Defra on synthetic biology for policy makers. We also aim to interact with policy makers through the EPSRC, BBSRC or other research councils.

Staff employed on the grant will be trained in state-of-the-art technologies in (i) synthetic biology and (ii) single molecule studies. This will make them valuable to both the academic and private sector. Cardiff University runs an extensive staff development program with a wide variety of courses, ranging from research-related development to project management to leadership skills, which the PDRA will attend. Costs are covered by the Schools. The applicants will participate in the training in scientific methodology, outreach through SMS, and encourage the development of ideas and promote the PDRA's progression as an independent scientist.

The planned research is not directed at immediate technological application, but integration of protein molecules with graphene has a clear longer-term potential for novel routes to bioelectronic sensors, or even electronic control of biological events. We shall therefore actively explore avenues to apply the findings of our programme in this area. The procedures in place at Cardiff University ensure that research is constantly reviewed with the aim of identifying areas that merit patent protection. This works via the University's Research and Commercial Development (RACD) division who operate a Commercial Advisory Panel and who are are prepared to meet the costs involved. Commercial exploitation of our work would be of benefit to the researchers, Cardiff University and the UK technology base as a whole.