Combining NMR docking data with EPR distances and in silico calculations for a more complete model of colicin protein-protein interactions

<p>Traditional methods of atomic resolution structure determination are commonly restricted to X-ray crystallography or NMR. Development of the fields have yielded more and better structures , yet many proteins remain unable to crystallise or unsuitable for NMR. In the pursuit of biologically relevant mechanistic function it is becoming more important to not only know the lone structure of a protein but how proteins interact and combine into complexes.</p> <p>The site directed spin labelling of proteins in combination with electron paramagnetic resonance (EPR) allows for further determination of protein-protein as well as protein-membrane interactions. Power saturation studies give the spin labels accessibility to water and phospholipid environments, whilst pulsed electron double resonance (PELDOR) studies give precise measurements of intra and intermolecular distances. Spin labelling at several sites within a complex allows for a complex three dimensional model to be built which can be combined with classical structural methods for comprehensive docking models.</p> <p>Here we use the well-characterised system of colicin E9 and its cognate inhibitor, Im9 to develop modelling methods to enhance existing docking models before application to previously untested non-cognate inhibitors to colicin E9.</p> <p> </p>