title: Tuberous sclerosis tumor suppressor complex-like complexes act as GTPase-activating proteins for Ral GTPases.
abstract: The small GTPases RalA and RalB are multifunctional proteins regulating a variety of cellular processes. Like other GTPases, the activity of Ral is regulated by the opposing effects of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Although several RalGEFs have been identified and characterized, the molecular identity of RalGAP remains unknown. Here, we report the first molecular identification of RalGAPs, which we have named RalGAP1 and RalGAP2. They are large heterodimeric complexes, each consisting of a catalytic alpha1 or alpha2 subunit and a common beta subunit. These RalGAP complexes share structural and catalytic similarities with the tuberous sclerosis tumor suppressor complex, which acts as a GAP for Rheb. In vitro GTPase assays revealed that recombinant RalGAP1 accelerates the GTP hydrolysis rate of RalA by 280,000-fold. Heterodimerization was required for this GAP activity. In PC12 cells, knockdown of the beta subunit led to sustained Ral activation upon epidermal growth factor stimulation, indicating that the RalGAPs identified here are critical for efficient termination of Ral activation induced by extracellular stimuli. Our identification of RalGAPs will enable further understanding of Ral signaling in many biological and pathological processes.
authors.affiliation: Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Shirakawa
authors.forename: Shuya
authors.initials: S
authors.lastname: Fukai
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Kawato
authors.forename: Tomohito
authors.initials: T
authors.lastname: Higashi
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kondo
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Ikeda
authors.forename: Ei
authors.initials: E
authors.lastname: Nakayama
authors.forename: Katsuya
authors.initials: K
authors.lastname: Okawa
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kimura
authors.forename: Toru
authors.initials: T
authors.lastname: Kita
authors.forename: Hisanori
authors.initials: H
authors.lastname: Horiuchi
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002384:Catalysis; D003600:Cytosol / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D008969:Molecular Sequence Data; D016716:PC12 Cells; D051381:Rats; D013552:Swine; D014018:Tissue Distribution; D014402:Tuberous Sclerosis / Q000378:metabolism*; D020725:ral GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; D020558:GTP Phosphohydrolases; D020725:ral GTP-Binding Proteins