Structure of the GTPase-binding domain of Sec5 and elucidation of its Ral binding site.
The exocyst complex is involved in the final stages of exocytosis, when vesicles are targeted to the plasma membrane and dock. The regulation of exocytosis is vital for a number of processes, for example, cell polarity, embryogenesis, and neuronal growth formation. Regulation of the exocyst complex in mammals was recently shown to be dependent upon binding of the small G protein, Ral, to Sec5, a central component of the exocyst. This interaction is thought to be necessary for anchoring the exocyst to secretory vesicles. We have determined the structure of the Ral-binding domain of Sec5 and shown that it adopts a fold that has not been observed in a G protein effector before. This fold belongs to the immunoglobulin superfamily in a subclass known as IPT domains. We have mapped the Ral binding site on this domain and found that it overlaps with protein-protein interaction sites on other IPT domains but that it is completely different from the G protein-geranyl-geranyl interaction face of the Ig-like domain of the Rho guanine nucleotide dissociation inhibitor. This mapping, along with available site-directed mutagenesis data, allows us to predict how Ral and Sec5 may interact.
Mott
Helen R
HR
Department of Biochemistry, University of Cambridge, 80, Tennis Court Road, Cambridge CB2 1GA, United Kingdom. mott@bio.cam.ac.uk
Nietlispach
Daniel
D
Hopkins
Louise J
LJ
Mirey
Gladys
G
Camonis
Jacques H
JH
Owen
Darerca
D
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004926:Escherichia coli; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D033921:Vesicular Transport Proteins; D020725:ral GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
C511409:Exoc2 protein, mouse; D008565:Membrane Proteins; D033921:Vesicular Transport Proteins; D020558:GTP Phosphohydrolases; D020725:ral GTP-Binding Proteins