Silicon transport proteins: from membrane protein biophysics to bionanoscience

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Nanotechnology will change the world by ushering in a new era of high-performance materials with applications in healthcare, agriculture, energy, biotechnology, computing, environmental technology and more. One of the central pillars of this revolution will be organic and inorganic materials with dimensions on the order of 1-100 nanometres. These nano-sized particles, or nanoparticles, behave differently to bulk materials because of their high surface-to-volume ratio and size-dependent quantum effects. Many nanoparticles have novel or enhanced optical, physicochemical and magnetic properties and will either improve existing products or provide a platform for new technologies as sensors, optical tools, biomarkers, therapeutics, catalysts and electronic components. These advances will depend upon synthetic methods that can generate particles of a defined size, shape and composition that are stable and do not aggregate. However, fulfilling all of these criteria remains a challenging technical goal and new synthetic routes will be critical in realising the full promise of nanoparticle technology. Intriguingly, biology - which can be considered to be the living embodiment of functional nanotechnology - provides numerous examples of nanomaterials that are assembled very precisely from simple precursors under mild synthetic conditions. This leads to the hypothesis: can we learn new tricks from biology to develop fresh prospects in nanoparticle synthesis? The proposal will address this hypothesis by using silica transport proteins as novel devices in nanoscale fabrication. The silica transporters (SITs) are a unique family of integral membrane proteins that are able to bind a soluble form of silica, silicic acid, with high affinity and transport it across the cell membrane into the cell. This activity is used by microscopic single-celled organisms to help build 'glass houses' around themselves. However, the precise details of silica transport are currently not well understood. The proposal aims to (i) discover the molecular basis for silica recognition and transport by the SITs and (ii) apply that understanding in the synthesis of silica nanoparticles. The first of these aims will be addressed by in vitro studies of SIT structure and function. This classical biochemical approach will provide an unprecedented insight into the only high-affinity protein-silica interaction found in nature. The second aim will be met by reconstituting SIT proteins into spherical lipid vesicles and transporting silica into the vesicle interior, so that the vesicles become nanoscale reaction chambers for the preparation of silica nanoparticles. These nanoreactors will have the advantages of exquisite kinetic control over substrate delivery to the growing nanoparticle and stringent regulation of particle composition and the synthetic environment. This latter benefit will be particularly useful for the controlled synthesis of composite or functionalized nanoparticles. The proposal thus presents one of the first examples of combining membrane protein science with inorganic chemistry and offers new horizons in biological nanoscience. It will provide a platform for a range of further developments in this area.