Structures of Heterotrimeric G Proteins and their Complexes

This chapter describes the three-dimensional structures of many of the components of the signal transduction cycle in several functionally relevant states. These structures provide insight into the molecular mechanics of G protein-mediated signal transduction. It discusses the molecular processes that constitute the signaling pathway. This area of research has been extensively reviewed. Heterotrimeric G proteins comprise two functional components: Gα subunits are GTP binding proteins and, when bound to GTP, preferentially interact with effectors. Crystal structures are determined for at least one representative of each class of Gα subunits, in some cases in both GTP-bound (with the use of non-hydrolyzible analogs) and GDP-bound states. Structures of several Gα proteins have been determined bound to the complex of GDP, tetrafluoroaluminate (AlF), and magnesium ion, which together mimic the transition state for GTP hydrolysis in which the phosphate is pentacoordinate.