Engineering principles of chemotaxis signalling pathways

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A vast amount of biological data has been accumulated over the last few decades focusing on properties of single molecules and qualitative changes in cell morphology due to genetic manipulation. However, very little is known about the engineering principles of the underlying biological pathways inside cells, i.e. how complete pathways work, what types of signals they process, how they deal with noise, and what they are optimized for. The chemotaxis pathways are a model for how cells process information about their environments to sense and move towards chemicals. In particular, the chemotaxis pathway in the bacterium E. coli is one of the very few fully characterized signalling pathways in any organism. We have begun to develop the computational tools for understanding how the complete pathway processes the signals by modelling experimental data of the cell's 'output' to a well-defined 'input', e.g. to a change of a chemical in the environment. Much less is known about the chemotaxis pathways in higher single-cell organisms and cells of our immune system. However, it is well established that cells are able to respond to tiny changes of chemicals in their environment. From a theoretical standpoint the distribution of chemoreceptors on the cell surface is crucial for this high sensitivity. These receptor distributions are qualitatively known for various organisms based on new high-resolution imaging techniques. We have begun developing a theory of how accurately chemicals can be measured by cell-surface receptors. We will extend this method to obtain the optimal receptor distribution for the most accurate measurement of chemicals.