Physics of Life - Noise, Information and Evolution in Protein Binding

How does order emerge from chaos? As if the 'miracle of life' in all its complexity were not enough to astonish us, the molecular story of how the information and energy flows occur within living cells and organisms tells an even stranger tale. For at the dimensions of life's molecular building blocks - the long protein molecules that fold up perfectly into functional forms, the even longer DNA that codes for the structure of its organisms, the cell membranes that marshal biochemical traffic between the cell and its surroundings - all these are subject to continual, rapid random fluctuation. The thermal jostling of every component seems, at first, to fight against the appearance of the order and structure that are the emergent signs of life. However, recent interdisciplinary collaborations between physicists and biologists have begun to discover just how deeply life has evolved to work with the noisy fluctuations rather than to fight them. This project will devote 5 years of focussed research to explore in detail three fundamental ways in which randomness and noise are recruited in biology, bringing the experience of the proposed Fellow, two post-doctoral research fellows and an extensive community of collaborators, to bear. The first example is right at the heart of information-processing in cells. 'Allostery' is the effect by which a protein molecule binds to another molecule (either a smaller species, or a giant molecule like DNA) if and only if a second 'signalling' molecule is also bound to it, at a different site. The presence of the signalling molecule is felt 'at a distance' at the other binding site. We will develop theoretical and computational tools to explore how the background of thermal fluctuations can be used to carry the signal, and learn from biology about the physics of fluctuating elastic matter. The second example continues the theme of protein-binding, but now to other proteins. The outstanding properties of spider and silkworm silk are even more outstanding when we discover how the fibres are made in nature. Somehow the molecular 'stickiness' of silk proteins is just enough to trigger their assembly into fibres when just the right flow conditions apply (at the spinneret). Working closely with experimental colleagues, we will develop theories of assembly in flow to help find out what makes silk, and its processing, so remarkable. A third stream of work takes the idea of random motion but now at the higher level of evolution itself. The search for the protein structures that deliver the binding properties of signalling and silk takes place in an unimaginably vast space of possibilities coded by the organism's genome. Random jumps in this space, like the random motions of the proteins themselves, somehow serve to find solutions, rather than frustrate them. We have an exciting opportunity to use the methods of 'noisy physics' at the molecular level to explore the physics of evolution itself, asking the question. 'How does nature search for, and find solutions?'. Completing the circle of the project, we will construct theories for the evolution of the sticky proteins themselves.