title: GAP1 family members constitute bifunctional Ras and Rap GTPase-activating proteins.
abstract: GAP1(IP4BP) is a member of the GAP1 family of Ras GTPase-activating proteins (Ras GAPs) that includes GAP1(m), CAPRI, and RASAL. Composed of a central Ras GAP domain, surrounded by amino-terminal C(2) domains and a carboxyl-terminal pleckstrin homology/Bruton's tyrosine kinase domain, GAP1(IP4BP) has previously been shown to possess an unexpected GAP activity on the Ras-related protein Rap, besides the predicted Ras GAP activity (Cullen, P. J., Hsuan, J. J., Truong, O., Letcher, A. J., Jackson, T. R., Dawson, A. P., and Irvine, R. F. (1995) Nature 376, 527-530). Here we have shown that GAP1(IP4BP) is indeed an efficient Ras/Rap GAP, having K(m)s of 213 and 42 microm and estimated k(cat)s of 48 and 16 s(-1) for Ras and Rap, respectively. For this dual activity, regions outside the Ras GAP domain are required, as the isolated domain (residues 291-569) retains a pronounced Ras GAP activity yet has very low activity toward Rap. Interestingly, mutagenesis of the Ras GAP arginine finger, and surrounding residues important in Ras binding, inhibit both Ras and Rap GAP activity of GAP1(IP4BP). Although the precise details by which GAP1(IP4BP) can function as a Rap GAP remain to be determined, these data are consistent with Rap associating with GAP1(IP4BP) through the Ras-binding site within the Ras GAP domain. Finally, we have established that such dual Ras/Rap GAP activity is not restricted to GAP1(IP4BP). Although GAP1(m) appears to constitute a specific Ras GAP, CAPRI and RASAL display dual activity. For CAPRI, its Rap GAP activity is modulated upon its Ca(2+)-induced association with the plasma membrane.
authors.affiliation: Henry Wellcome Integrated Signaling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Sabine
authors.initials: S
authors.lastname: Kupzig
authors.forename: Delia
authors.initials: D
authors.lastname: Deaconescu
authors.forename: Dalila
authors.initials: D
authors.lastname: Bouyoucef
authors.forename: Simon A
authors.initials: SA
authors.lastname: Walker
authors.forename: Qing
authors.initials: Q
authors.lastname: Liu
authors.forename: Christian L
authors.initials: CL
authors.lastname: Polte
authors.forename: Oliver
authors.initials: O
authors.lastname: Daumke
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Ishizaki
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lockyer
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cullen
mesh_terms: D000818:Animals; D001120:Arginine / Q000737:chemistry; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D066298:In Vitro Techniques; D007700:Kinetics; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D009711:Nucleotides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000502:physiology*; D014162:Transfection; D020703:ras GTPase-Activating Proteins / Q000378:metabolism
chemical_list: D009711:Nucleotides; D018160:Receptors, Cytoplasmic and Nuclear; C061107:inositol-1,3,4,5-tetrakisphosphate receptor; D020703:ras GTPase-Activating Proteins; D001120:Arginine; D002118:Calcium