Taxonomic distribution of proteins containing RhoGAP domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing RhoGAP domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Oligophrenin-1 encodes a rhoGAP protein involved in X-linked mental retardation.

Billuart P, Bienvenu T, Ronce N, desPortes V, Vinet MC, Zemni R, RoestCrollius H, Carrie A, Fauchereau F, Cherry M, Briault S, Hamel B, Fryns JP, Beldjord C, Kahn A, Moraine C, Chelly J
Nature. 1998; 392: 923-6

Primary or nonspecific X-linked mental retardation (MRX) is a heterogeneous condition in which affected patients do not have any distinctive clinical or biochemical features in common apart from cognitive impairment. Although it is present in approximately 0.15-0.3% of males, most of the genetic defects associated with MRX, which may involve more than ten different genes, remain unknown. Here we report the characterization of a new gene on the long arm of the X-chromosome (position Xq12) and the identification in unrelated individuals of different mutations that are predicted to cause a loss of function. This gene is highly expressed in fetal brain and encodes a protein of relative molecular mass 91K, named oligophrenin-1, which contains a domain typical of a Rho-GTPase-activating protein (rhoGAP). By enhancing their GTPase activity, GAP proteins inactivate small Rho and Ras proteins, so inactivation of rhoGAP proteins might cause constitutive activation of their GTPase targets. Such activation is known to affect cell migration and outgrowth of axons and dendrites in vivo. Our results demonstrate an association between cognitive impairment and a defect in a signalling pathway that depends on a Ras-like GTPase.

The structure of the GTPase-activating domain from p50rhoGAP.

Barrett T, Xiao B, Dodson EJ, Dodson G, Ludbrook SB, Nurmahomed K, Gamblin SJ, Musacchio A, Smerdon SJ, Eccleston JF
Nature. 1997; 385: 458-61

Members of the Rho family of small G proteins transduce signals from plasma-membrane receptors and control cell adhesion, motility and shape by actin cytoskeleton formation. They also activate other kinase cascades. Like all other GTPases, Rho proteins act as molecular switches, with an active GTP-bound form and an inactive GDP-bound form. The active conformation is promoted by guanine-nucleotide exchange factors, and the inactive state by GTPase-activating proteins (GAPs) which stimulate the intrinsic GTPase activity of small G proteins. Rho-specific GAP domains are found in a wide variety of large, multi-functional proteins. Here we report the crystal structure of an active 242-residue C-terminal fragment of human p50rhoGAP. The structure is an unusual arrangement of nine alpha-helices, the core of which includes a four-helix bundle. Residues conserved across the rhoGAP family are largely confined to one face of this bundle, which may be an interaction site for target G proteins. In particular, we propose that Arg 85 and Asn 194 are involved in binding G proteins and enhancing GTPase activity.

Structural determinants required for the interaction between Rho GTPase and the GTPase-activating domain of p190.

Li R, Zhang B, Zheng Y
J Biol Chem. 1997; 272: 32830-5

The Rho family small GTP-binding proteins are subjected to regulation by Rho GTPase-activating proteins (GAPs) in the course of transmitting diverse intracellular signals. To understand the mechanism of GAP-catalyzed GTP hydrolysis of Rho GTPases, we have studied the interaction between RhoA and p190, the RasGAP binding phosphoprotein which has been implicated as a Rho-specific GAP, by delineating the structural determinants of RhoA and p190 GAP domain (p190GD) that are involved in their functional coupling. Besides the conserved residues Tyr34, Thr37, and Phe39 in the switch I region of RhoA which are required for p190GD interaction, chimeras made between RhoA and Cdc42, a close relative of RhoA with which p190GD interacts 50-fold less efficiently, revealed that residues outside the switch I and neighboring regions of RhoA, residues 85-122 in particular, contain the major p190GD-specifying determinant(s). Mutation of the unique Asp90 of RhoA in this region mostly abolished p190GD stimulation, whereas the corresponding reverse mutation of Cdc42 (S88D) was able to respond to p190GD-catalysis similarly as RhoA. Further kinetic analysis of these mutants provided evidence that Asp90 of RhoA contributes primarily to the specific binding interaction with p190GD. On the other hand, two charged residues of p190GD, Arg1283 and Lys1321, which are located in the putative G-protein binding helix pocket of GAP domain, were found to be involved in different aspects of interaction with RhoA. The R1283L mutant of p190GD lost GAP activity but retained the ability to bind to RhoA, while K1321A failed to stimulate and to bind to RhoA. These results indicate that residue Asp90 constitutes the second GAP-interactive site in RhoA which is mostly responsible for conferring p190GD-specificity, and suggest that the role of p190GD in the GTPase reaction of RhoA is in part to supply active site residue Arg1283 for efficient catalysis.

Structure at 1.65 A of RhoA and its GTPase-activating protein in complex with a transition-state analogue.

Rittinger K, Walker PA, Eccleston JF, Smerdon SJ, Gamblin SJ
Nature. 1997; 389: 758-62

Small G proteins of the Rho family, which includes Rho, Rac and Cdc42Hs, regulate phosphorylation pathways that control a range of biological functions including cytoskeleton formation and cell proliferation. They operate as molecular switches, cycling between the biologically active GTP-bound form and the inactive GDP-bound state. Their rate of hydrolysis of GTP to GDP by virtue of their intrinsic GTPase activity is slow, but can be accelerated by up to 10(5)-fold through interaction with rhoGAP, a GTPase-activating protein that stimulates Rho-family proteins. As such, rhoGAP plays a crucial role in regulating Rho-mediated signalling pathways. Here we report the crystal structure of RhoA and rhoGAP complexed with the transition-state analogue GDP.AlF4- at 1.65 A resolution. There is a rotation of 20 degrees between the Rho and rhoGAP proteins in this complex when compared with the ground-state complex Cdc42Hs.GMPPNP/rhoGAP, in which Cdc42Hs is bound to the non-hydrolysable GTP analogue GMPPNP. Consequently, in the transition state complex but not in the ground state, the rhoGAP domain contributes a residue, Arg85(GAP) directly into the active site of the G protein. We propose that this residue acts to stabilize the transition state of the GTPase reaction. RhoGAP also appears to function by stabilizing several regions of RhoA that are important in signalling the hydrolysis of GTP.

Crystal structure of a small G protein in complex with the GTPase-activating protein rhoGAP.

Rittinger K, Walker PA, Eccleston JF, Nurmahomed K, Owen D, Laue E, Gamblin SJ, Smerdon SJ
Nature. 1997; 388: 693-7

Small G proteins transduce signals from plasma-membrane receptors to control a wide range of cellular functions. These proteins are clustered into distinct families but all act as molecular switches, active in their GTP-bound form but inactive when GDP-bound. The Rho family of G proteins, which includes Cdc42Hs, activate effectors involved in the regulation of cytoskeleton formation, cell proliferation and the JNK signalling pathway. G proteins generally have a low intrinsic GTPase hydrolytic activity but there are family-specific groups of GTPase-activating proteins (GAPs) that enhance the rate of GTP hydrolysis by up to 10(5) times. We report here the crystal structure of Cdc42Hs, with the non-hydrolysable GTP analogue GMPPNP, in complex with the GAP domain of p50rhoGAP at 2.7A resolution. In the complex Cdc42Hs interacts, mainly through its switch I and II regions, with a shallow pocket on rhoGAP which is lined with conserved residues. Arg 85 of rhoGAP interacts with the P-loop of Cdc42Hs, but from biochemical data and by analogy with the G-protein subunit G(i alpha1), we propose that it adopts a different conformation during the catalytic cycle which enables it to stabilize the transition state of the GTP-hydrolysis reaction.

A novel GTPase-activating protein for Rho interacts with a PDZ domain of the protein-tyrosine phosphatase PTPL1.

Saras J, Franzen P, Aspenstrom P, Hellman U, Gonez LJ, Heldin CH
J Biol Chem. 1997; 272: 24333-8

PTPL1 is an intracellular protein-tyrosine phosphatase that contains five PDZ domains. Here, we present the cloning of a novel 150-kDa protein, the four most C-terminal amino acid residues of which specifically interact with the fourth PDZ domain of PTPL1. The molecule contains a GTPase-activating protein (GAP) domain, a cysteine-rich, putative Zn2+- and diacylglycerol-binding domain, and a region of sequence homology to the product of the Caenorhabditis elegans gene ZK669.1a. The GAP domain is active on Rho, Rac, and Cdc42 in vitro but with a clear preference for Rho; we refer to the molecule as PTPL1-associated RhoGAP 1, PARG1. Rho is inactivated by GAPs, and protein-tyrosine phosphorylation has been implicated in Rho signaling. Therefore, a complex between PTPL1 and PARG1 may function as a powerful negative regulator of Rho signaling, acting both on Rho itself and on tyrosine phosphorylated components in the Rho signal transduction pathway.

Crystal structure of the breakpoint cluster region-homology domain from phosphoinositide 3-kinase p85 alpha subunit.

Musacchio A, Cantley LC, Harrison SC
Proc Natl Acad Sci U S A. 1996; 93: 14373-8

Proteins such as the product of the break-point cluster region, chimaerin, and the Src homology 3-binding protein 3BP1, are GTPase activating proteins (GAPs) for members of the Rho subfamily of small GTP-binding proteins (G proteins or GTPases). A 200-residue region, named the breakpoint cluster region-homology (BH) domain, is responsible for the GAP activity. We describe here the crystal structure of the BH domain from the p85 subunit of phosphatidylinositol 3-kinase at 2.0 A resolution. The domain is composed of seven helices, having a previously unobserved arrangement. A core of four helices contains most residues that are conserved in the BH family. Their packing suggests the location of a G-protein binding site. This structure of a GAP-like domain for small GTP-binding proteins provides a framework for analyzing the function of this class of molecules.

Proteins regulating Ras and its relatives.

Boguski MS, McCormick F
Nature. 1993; 366: 643-54

GTPases of the Ras superfamily regulate many aspects of cell growth, differentiation and action. Their functions depend on their ability to alternate between inactive and active forms, and on their cellular localization. Numerous proteins affecting the GTPase activity, nucleotide exchange rates and membrane localization of Ras superfamily members have now been identified. Many of these proteins are much larger and more complex than their targets, containing multiple domains capable of interacting with an intricate network of cellular enzymes and structures.

Characterization of two 85 kd proteins that associate with receptor tyrosine kinases, middle-T/pp60c-src complexes, and PI3-kinase.

Otsu M, Hiles I, Gout I, Fry MJ, Ruiz-Larrea F, Panayotou G, Thompson A, Dhand R, Hsuan J, Totty N, etal.
Cell. 1991; 65: 91-104

Affinity-purified bovine brain phosphatidylinositol 3-kinase (PI3-kinase) contains two major proteins of 85 and 110 kd. Amino acid sequence analysis and cDNA cloning reveals two related 85 kd proteins (p85 alpha and p85 beta), which both contain one SH3 and two SH2 regions (src homology regions). When expressed, these 85 kd proteins bind to and are substrates for tyrosine-phosphorylated receptor kinases and the polyoma virus middle-T antigen/pp60c-src complex, but lack PI3-kinase activity. However, an antiserum raised against p85 beta immunoprecipitates PI3-kinase activity. The active PI3-kinase complex containing p85 alpha or p85 beta and the 110 kd protein binds to PDGF but not EGF receptors. p85 alpha and p85 beta may mediate specific PI3-kinase interactions with a subset of tyrosine kinases.