A Built-in Arginine Finger Triggers the Self-stimulatory GTPase-activating Activity of Rho Family GTPases

Abstract

Signal transduction through the Rho family GTPases requires regulated cycling of the GTPases between the active GTP-bound state and the inactive GDP-bound state. Rho family members containing an arginine residue at position 186 in the C-terminal polybasic region were found to possess a self-stimulatory GTPase-activating protein (GAP) activity through homophilic interaction, resulting in significantly enhanced intrinsic GTPase activities. This arginine residue functions effectively as an "arginine finger" in the GTPase activating reaction to confer the catalytic GAP activity but is not essential for the homophilic binding interactions of Rho family proteins. The arginine 186-mediated negative regulation seems to be absent from Cdc42, a Rho family member important for cell-division cycle regulation, of lower eukaryotes, yet appears to be a part of the turn-off machinery of Cdc42 from higher eukaryotes. Introduction of the arginine 186 mutation into S. cerevisiae CDC42 led to phenotypes consistent with down-regulated CDC42 function. Thus, specific Rho family GTPases may utilize a built-in arginine finger, in addition to RhoGAPs, for negative regulation.

The Trans-autostimulatory Activity of Rad27 Suppresses dna2 Defects in Okazaki Fragment Processing

“…To date, only a few examples of self-stimulatory enzymes have been reported. One example is the self-stimulatory GTPase-activating activity of RhoC, Cdc42Hs, and Rac2, the Rho family GTPases (45,46). The rate of GTP hydrolysis by RhoC was increased significantly by increasing levels of GTP-bound RhoC, whereas RhoA and RhoB, despite their high sequence homology with RhoC, have a slow constant rate of GTP hydrolysis in a dose-independent manner (46).…”

Rho GTPase activity zones and transient contractile arrays

“…(7) Rac-GTP promotes actin assembly by activation of the WAVE complex and other targets, (8) while Cdc42-GTP binds and activates N-WASP, which activates the Arp2/3 complex, thereby promoting formation of branched actin filament networks. (9) Because the Rho GTPases are intrinsically inefficient enzymes, hydrolyzing a single GTP every 5-50 minutes, (10) most of the regulation of the Rho GTPase cycle depends on several classes of regulatory proteins: (1) guanine nucleotide exchange factors (GEFs) promote the exchange of GDP for GTP, (2) GTPase activating proteins (GAPs) promote GTP hydrolysis, and (3) guanine nucleotide dissociation inhibitors (GDIs) stabilize the GDP-bound state and mask the lipid moeity, facilitating cytoplasmic solubility for GTPases. (11,12) The standard view of the role of Rho regulators is that a given actin-dependent process is initiated primarily by GEF-dependent Rho GTPase activation and eventually terminated by GAPdependent Rho GTPase inactivation, with GDIs passively converting inactivated Rho GTPases to a soluble form (Fig.…”

The arginine finger of bacteriophage T7 gene 4 helicase: Role in energy coupling

“…The arginine can reside on a distinct activator protein, as in the case of GAP-Ras (20,21), an adjacent subunit of an oligomeric protein such as the F 1 -ATPase (17), or a distinct domain within the protein itself (22). Arginine fingers contribute to NTP hydrolysis through stabilization of the transition state of the reaction and as a trigger for conformational changes after hydrolysis of dTTP (19,23,24).…”