Chemical and biophysical studies of ionic protein fluids

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When heated, many pure substances, for example metals, will melt and form liquids. One of the reasons that melting occurs is because the metal atoms are of a similar size to the distance over which the forces between them act. For large biological molecules like proteins however, heating the dry protein powder results in decomposition and the formation of a gas, i.e. there is no liquid phase. Polymers however, are also large molecules that do melt when heated (like melting plastic), and this is due in part to the greater distances over which the forces between the polymer molecules act. In the research proposed here, we wish to attach polymers to the surface of proteins so that proteins can form liquids with no water. The method for attaching the polymer to the protein involves the chemical modification of the protein surface to make it highly charged. The polymers are oppositely charged and as a result they bind electrostatically to the protein surface. Effectively, the polymers at the surface behave as a fluidization region and these molecules need to be selected carefully so that the modified proteins behave as a single entity and can be classified as true liquids. In recent studies we have achieved this by modifying the protein to give a highly positively charged surface, and then adding a negatively charged polymer surfactant. We then remove the unbound surfactant, freeze the sample, and carefully remove all the water by freeze-drying to produce a powder that melts at around 29 C, producing a liquid protein. We now wish to extend this method to produce a wide range of liquid proteins with different properties. We will study both the internal structure and the fluid properties of each protein liquid formed. The information gained about the internal structure will be used to help determine if the natural properties of the proteins are still present in the liquid state. After we understand the structure and how and why these liquid proteins form, we will use this information to develop new types of smart' materials using liquid proteins, e.g. for biosensors and for new types of wound dressing materials.