G-Protein Activation State-Selective Binding Peptides as New Tools for Probing Heterotrimeric G-protein Subunit Signaling Dynamics
- Pp. 219-247 (29)Christopher A. Johnston, Francis S. Willard, Kevin Ramer, Rainer Blaesius, Natalia Roques and David P. Siderovski
Heterotrimeric G-proteins, comprising G&#945;, G&#946;, and G&#947; subunits, are molecular switches that regulate numerous signaling pathways involved in cellular physiology. This characteristic is achieved by the adoption of two principal states: an inactive state in which GDP-bound G&#945; is complexed with the G&#946;&#947; dimer, and an active state in which GTP-bound G&#945; is freed of its G&#946;&#947; binding partner. Structural studies have illustrated the basis for the distinct conformations of these states which are regulated by alterations in three precise ‘switch regions’ of the G&#945; subunit. Discrete differences in conformation between GDP- and GTP-bound G&#945; underlie its nucleotide-dependent protein-protein interactions (e.g., with G&#946;&#947;/receptor and effectors, respectively) that are critical for maintaining their proper nucleotide cycling and signaling properties. Recently, several screening approaches have been used to identify peptide sequences capable of interacting with G&#945; (and free G&#946;&#947;) in nucleotidedependent fashions. These peptides have demonstrated applications in direct modulation of the nucleotide cycle, assessing the structural basis for aspects of G&#945; and G&#946;&#947; signaling, and serving as biosensor tools in assays for G&#945; activation including high-throughput drug screening. In this review, we highlight some of the methods used for such discoveries and discuss the insights that can be gleaned from application of these identified peptides.