Designing new materials that have small-scale (nanometre) structures and combine multiple components is expected to lead to the development of new technology in areas of sensing, electronics, catalysis and medicine. These materials can be difficult to synthesise, and a new approach is to use large biological molecules known as proteins as an active component. Proteins are made up of long chains of amino acids that fold upon themselves to form complex 3D structures. In the body, proteins perform a wide variety of tasks (or functions) from the binding of oxygen in muscles (which is performed by the protein myoglobin), to the storage of iron in the blood (ferritin), and it would be advantageous if these properties could be transferred to a synthetic material. Proteins are most commonly found either as dispersions in aqueous solutions or as dry powders, and it is fascinating to note that till recently, proteins in the pure liquid phase did not exist, i.e. heating a dry protein powder will not cause it to melt. In essence, this means that there was a missing phase of biological matter that was yet to be discovered.
The absence of a pure liquid protein phase results from the relatively large molecular dimensions (nanoscale) of the protein molecule, and is an intriguing phenomenon that is also seen with nanoparticles. The situation arises because the liquid phase of a material is stabilized by attractive inter-molecular forces that act over distances that are considerably larger than the size of the individual molecules. This is not the case for proteins however, as their structures are large compared with the range of the forces between them. In essence, the protein molecules are so firmly held together in the solid phase that heating would not make them melt, but rather, would destroy their molecular structure, resulting in decomposition.
The aim of my research is to design a universal approach to access the missing liquid phase of proteins by increasing the range of the attractive protein-protein interactions. To do this I will attach artificial (synthetic) polymer surfactant molecules to the proteins' surfaces to produce protein molecules with long tendrils that can interact with other protein molecules over longer distances. These polymer surfactant molecules are negatively charged, and only attach to positively charged groups on the protein surface. Hence it will be necessary to first chemically alter the surface of the protein molecules to make them more positively charged, so that enough of the polymer surfactant molecules can be attached. In my preliminary studies I used this approach to produce liquids of ferritin and myoglobin, which contained no water and melted near room temperature. What was truly astounding is that even though the protein molecules have evolved to operate in aqueous environments, their structures in the pure liquid phase appeared not to have changed, and in the case of myoglobin, the protein could still bind oxygen.
My proposed work allows me to apply my knowledge of biochemistry, materials science and physical chemistry to develop a new class of hybrid biological liquids, and I intend to develop this new approach to produce a wide range of liquid proteins with different functions. In each case I will investigate the molecular structure of the liquids, as well as their composition and properties such as viscosity, and I will also test the protein for function. This will not only provide a range of new active liquids, but will aid in the understanding of how important water is for protein structure and function. Finally, once I understand how these systems work, then I will use the results to develop new types of materials based on liquid proteins. For example, I intend to develop new biological sensors for the detection of toxic gases such as carbon monoxide, or active wound dressings that supply oxygen to the wound during healing.
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