Tuberous sclerosis tumor suppressor complex-like complexes act as GTPase-activating proteins for Ral GTPases.
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.
Shirakawa
Ryutaro
R
Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
Fukai
Shuya
S
Kawato
Mitsunori
M
Higashi
Tomohito
T
Kondo
Hirokazu
H
Ikeda
Tomoyuki
T
Nakayama
Ei
E
Okawa
Katsuya
K
Nureki
Osamu
O
Kimura
Takeshi
T
Kita
Toru
T
Horiuchi
Hisanori
H
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*
D020690:GTPase-Activating Proteins; D020558:GTP Phosphohydrolases; D020725:ral GTP-Binding Proteins