A novel biophysical method for the study of tethered signalling reactions

Many signalling reactions depend on the signalling protein first localising near its substrate before catalysing a reaction. A common example is the binding of cytosolic enzymes to the unstructured cytoplasmic tails of immune receptors. The tethering (binding) of these enzymes to the tails of immune receptors influences the local concentration of substrate that they experience. In contrast to cytosolic reactions, we currently do not have experimental tools to study tethered signalling reactions. In this work-in-progress talk, I will present an experimental assay that we have been using to study tethered signalling. I will show that the PDE model fails to fit the data (which is averaged over moles of protein) whereas the equivalent stochastic simulation can fit the data. We derived a modified PDE model based on a pair density formalism that can fit the data and the stochastic simulation. Ultimately, we are able to recover 4 parameters that characterise a tethered signalling reaction from the data: binding rates, catalytic rate, and a parameter that determines the properties of the tether.