The structure of an Arf-ArfGAP complex reveals a Ca2+ regulatory mechanism.
Arfs are small G proteins that have a key role in vesicle trafficking and cytoskeletal remodeling. ArfGAP proteins stimulate Arf intrinsic GTP hydrolysis by a mechanism that is still unresolved. Using a fusion construct we solved the structure of the ArfGAP ASAP3 in complex with Arf6 in the transition state. This structure clarifies the ArfGAP catalytic mechanism and shows a glutamine((Arf6)) and an arginine finger((ASAP3)) as the important catalytic residues. Unexpectedly the structure shows a calcium ion, liganded by both proteins in the complex interface, stabilizing the interaction and orienting the catalytic machinery. Calcium stimulates the GAP activity of ASAPs, but not other members of the ArfGAP family. This type of regulation is unique for GAPs and any other calcium-regulated processes and hints at a crosstalk between Ca(2+) and Arf signaling.
Ismail
Shehab A
SA
Department of Structural Biology, Max-Planck-Institute für Molekulare Physiologie, Dortmund 44227, Germany.
Vetter
Ingrid R
IR
Sot
Begona
B
Wittinghofer
Alfred
A
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D020690:GTPase-Activating Proteins / Q000737:chemistry* / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D054730:Protein Interaction Domains and Motifs; D016415:Sequence Alignment
D000089982:ADP-Ribosylation Factor 6; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate; C488555:ASAP3 protein, human; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; D002118:Calcium