Nanoscale patterning of engineered light harvesting complexes.

Lead Research Organisation: University of Sheffield
Department Name: Molecular Biology and Biotechnology


Nature makes tiny machines / membranes and protein complexes - that are up to ten times smaller than the smallest object our chip making technology can make, but it builds them up from many smaller pieces / amino acids / which is a much more efficient process. In order to make devices from Nature's machines we need to adopt a similar approach and build them from individual proteins. Our work examines a particular type of protein, a light-harvesting complex (LHC), that can capture light and pass it along a network of identical LHCs to a specialised protein, the reaction centre (RC). The RC protein converts the light energy to chemical energy in the form of a proton gradient / akin to charging up a biological battery. We will use the LHC as a model system, one which we can test our ideas upon, before attempting similar experiments with larger more complex proteins. The LHC captures light, so it is easy to discover whether anything that we have done to the LHC has damaged it, simply by shining light on it and measuring if it is still able to capture the light. We are attempting to join the LHC to an electronic chip, not to make something we need right now but to show that we can make a hybrid system from biological and non-biological components. Why should we be attempting this ? Until very recently electronic chips contained only inorganic materials but now there is a growing interest in using proteins that nature has already designed for a specific job, eg to detect a precise smell, to do the same for us on a chip. Unfortunately proteins are very fragile and cannot easily be placed exactly where they are needed on a chip as they are too small to physically pick up. We need to find ways of 'telling' the protein where we want it to be so that it does the work for us and binds to the right point on the chip. Nature has developed ways of telling a protein what it should attach itself to and what it should not attach itself to, therefore we must learn how this is done so that we can make a 'smart' material that 'tells' the protein 'attach yourself here'. Our research will use the LHCs to help us learn these natural direction instructions and we will know when we have succeeded because the LHC will act as a tiny beacon when we shine light upon it, effectively saying 'here I am, right where you wanted me to be'. Once we have this knowledge it can then be applied in more practical ways, for example to make hybrid chips that make use of proteins to detect poisons or pollutants at levels far lower than conventional detectors can.

Technical Summary

This work is aimed at acquiring fundamental knowledge about how membrane proteins interact with chemically defined substrates and conductive surfaces. The work is to be conducted in 3 complementary streams:- 1. Protein Patterning on Defined Substrates:- Self Assembled Monolayers (SAM) 2. Tripartite Protein Patterning 3. Electronic Properties of Proteins Most of the basic knowledge of membrane protein interactions with defined surfaces is expected to flow from Streams 1 & 3 where we will be examining methods of directed association of the purple bacterial light-harvesting (LH) and reaction centre (RC) membrane proteins with surfaces of defined chemical nature (Stream 1). We will use atomic force and fluorescence microscopy (AFFM) to establish both the presence and activity of the LH complexes attached to the SAMs. The induced vectorial flow of electrons through the LH and RC that are attached to a conductive gold surface, at the single molecule level, will be measured by scanning tunnelling microscopy (STM) under physiological conditions to maintain LH complex function (Stream 3). Stream 2 should realise generally applicable protocols for the precision attachment of the LH and other membrane proteins to patterned SAMs. The work will utilise knowledge from Stream 1 to choose the most effective surface chemistries to allow up to three different proteins to be patterned adjacent to each other. The close physical contact of the proteins will be tested using the transfer of excitation energy which can only occur if the proteins are less than a nanometre apart. A second patterning regime which exposes the gold substrate sequentially by photolithography in order to bind mutant versions of up to three proteins will also be attempted and tested by excitation energy transfer. The results of these two trials at the microscale will determine which patterning strategy to use in attempting a nanoscale tripartite protein patterning.


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