Complex Reconstitution from Individual Protein Modules.

Cellular function relies on protein complexes that work as nano-machines. The structure and function of protein complexes is an outcome of the specific combination of protein subunits, or modules, within the complex. A major focus of molecular biology is thus to understand how protein subunits assemble to form complexes with distinct biological function. To this end, in vitro reconstitution of complexes from individual subunits to study their assembly, structure and activity is of central importance. With purified individual subunits and sub-modules at hand one can systematically dissect the hierarchical assembly of larger complexes using direct protein-protein interaction assays. Furthermore, activity assays can be carried out with individual subunits or smaller sub-complexes and compared to those of the fully assembled complex to precisely map functional sites and provide a molecular basis for in vivo observations. In this chapter we review methods for protein complex assembly from individual subunits and provide examples of advantages and potential pitfalls to this approach.