Mechanisms of dominant negative G-protein alpha subunits.

G-protein-coupled receptors (GPCRs) represent the largest class of membrane proteins and are the targets of 25-50% of drugs currently on the market. Dominant negative mutant Galpha subunits of heterotrimeric G-proteins have been extensively utilized to delineate G-protein signaling pathways and represent a promising new tool to study GPCR-dependent signaling in the CNS. There are different regions in various types of Galpha subunits in which mutations can give rise to a dominant negative phenotype. Such a mutant Galpha would compete with wild-type Galpha for binding to other proteins involved in the G-protein cycle and either block or reduce the response caused by wild-type Galpha. To date, there are three different mechanisms described for dominant negative Galpha subunits: sequestration of the Gbetagamma subunits, sequestration of the activated GPCR by the heterotrimeric complex, and sequestration of the activated GPCR by nucleotide-free Galpha. This review focuses on the development of dominant negative Galpha subunits, the different mechanisms used by various mutant Galpha subunits, and potential structural changes underlying the dominant negative effects. (c) 2007 Wiley-Liss, Inc.