Protein-protein interactions of the BCL-2 family

The BCL-2 family of proteins are important regulators of mitochondrial apoptosis, comprising both pro- and anti-apoptotic members that interact with one another at the mitochondrial outer membrane to determine cellular fate. Dysregulation of their activities in the cell is implicated in many forms of cancer; the development of molecules able to mimic and modulate their interactions is thus highly desirable and has been the subject of a great deal of research effort. The use of techniques including structure based design and peptidomimetic approaches has produced some notable successes in this area, but few have successfully transitioned from laboratory to clinic, and the search for more and better ways to develop such molecules continues. In this thesis, I present a novel approach to identifying binding partners for BCL-2 proteins, which uses phage display experiments and the production of non-antibody scaffold proteins called Affimers. Five BCL-2 family proteins were selected as targets for study, comprising a good cross section of proand anti-apoptotic members. In the following chapters, I first describe the work undertaken to purify and characterise these target proteins, then detail the work done to identify and purify Affimer binding partners for each of them. Finally, I report on structural studies carried out to explore the mechanism by which BAX, a pro-apoptotic family member, forms death inducing oligomers. Taken together, the results of this project lay the foundations for further structural studies of BAX oligomerisation, and demonstrate that the use of phage display to generate selectively binding non-antibody scaffold proteins can provide useful additions to the existing array of BCL2 family interacting molecules.