Biochemical analyses of the Wrch atypical Rho family GTPases.

The Rho family of GTPases comprises a major branch of the Ras superfamily of small GTPases. To date, at least 22 human members have been identified. However, most of our knowledge of Rho GTPase function comes from the study of the three classical Rho GTPases, RhoA, Rac1, and Cdc42. These Rho GTPases function as GDP/GTP-related binary switches that are activated by diverse extracellular signal-mediated stimuli. The activated GTPases then interact with downstream effectors to regulate cytoplasmic signaling networks that in turn regulate actin organization, cell cycle progression, and gene expression. Recently, studies have begun to explore the regulation and function of some of the lesser-known members of the Rho GTPase family. Wrch-1 (Wnt-regulated Cdc42 homolog-1) and the closely related Chp (Cdc42 homologous protein)/Wrch-2 protein comprise a distinct branch of the mammalian Rho GTPase family. Although both share significant sequence and functional similarities with Cdc42, Wrch proteins possess additional N- and C-terminal sequences that distinguish them from the classical Rho GTPases (Cdc42, RhoA, and Rac1). We have determined that Wrch-1 and Wrch2 exhibit unusual GDP/GTP binding properties and undergo posttranslational lipid modifications distinct from those of the classical Rho GTPases. In this chapter, we summarize our experimental approaches used to characterize the biochemical properties of these atypical Rho GTPases.