Structure of the GTPase-binding Domain of Sec5 and Elucidation of its Ral Binding Site

Abstract

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. 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. Ral-binding protein 1 immunoglobulin Ig-like, plexins, transcription factors guanine nucleotide dissociation inhibitor nuclear magnetic resonance heteronuclear single quantum correlation nuclear Overhauser effect spectroscopy total correlation spectroscopy 3-(N-morpholino)propanesulfonic acid Spatial regulation of exocytosis is crucial for a variety of cellular processes, including embryogenesis, establishment and maintenance of cell polarity, and neuronal growth cone formation (reviewed in Ref. 1Hsu S.C. Hazuka C.D. Foletti D.L. Scheller R.H. Trends Cell Biol. 1999; 9: 150-153Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). The exocyst complex is involved in the final stage of exocytosis, when post-Golgi vesicles are targeted and dock to the plasma membrane. The exocyst consists of an assembly of eight proteins: Sec3, -5, -6, -8, -10, and 15, and Exo70 and -84, which form a complex localized to sites of vesicle docking to the plasma membrane during exocytosis.In Saccharomyces cerevisiae the exocyst directs vectorial targeting of secretory vesicles to sites of membrane expansion, such as bud sites. It appears that Sec3p, which is always localized to the plasma membrane, forms a targeting patch and is the spatial landmark for polarized exocytosis (reviewed in Ref. 1Hsu S.C. Hazuka C.D. Foletti D.L. Scheller R.H. Trends Cell Biol. 1999; 9: 150-153Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). A subcomplex of Sec15p and Sec10p is localized to secretory vesicles (2Guo W. Roth D. Walch-Solimena C. Novick P. EMBO J. 1999; 18: 1071-1080Crossref PubMed Scopus (496) Google Scholar) and a network of protein-protein interactions among the exocyst components bridges Sec15p-Sec10p to the targeting patch made by Sec3p (3Guo W. Grant A. Novick P. J. Biol. Chem. 1999; 274: 23558-23564Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar).In mammals the exocyst is involved in the targeting of Golgi-derived vesicles to the basolateral membrane of polarized epithelia. The regulation of the exocyst seems to be somewhat different in higher eukaryotes, because Sec3 does not have the same role. Rather, in polarized epithelial cells, Exo70 is localized to the plasma membrane (4Matern H.T. Yeaman C. Nelson W.J. Scheller R.H. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 9648-9653Crossref PubMed Scopus (95) Google Scholar), whereas the other components of the exocyst remain that exocyst assembly the membrane is dependent upon Sec3 as in of the superfamily are involved in the regulation of a variety of cellular processes, including nuclear and vesicle of exocytosis, it was that small a in exocyst regulation P. W. Trends Cell Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). a of Sec15p to secretory vesicles (2Guo W. Roth D. Walch-Solimena C. Novick P. EMBO J. 1999; 18: 1071-1080Crossref PubMed Scopus (496) Google Scholar). The exocyst is to the plasma membrane the interaction of Sec3p with W. Novick P. Cell Biol. 2001; PubMed Scopus Google Scholar). Sec3p has been shown to to of the Rho Novick P. W. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). it was shown that with the plasma membrane J. A. Biol. 1999; PubMed Google Scholar). The of the Rho which the in exocyst regulation a of with exocytosis.In cells, the exocyst components not to with Rho Rather, it was recently shown that the exocyst is by S. C. Cell Biol. PubMed Scopus Google S. A. Cell Biol. PubMed Scopus Google A. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google A. Biol. PubMed Scopus Google Scholar). Ral is a small G protein that is not in S. Ral and Ral polarized exocytosis in epithelial cells, it is necessary for the to the and forms to vesicle Ral, is localized to secretory vesicles and the plasma membrane, but the exocyst component for with was found to be is the of the exocyst the subcomplex to the of the exocyst interactions with Sec3p, and (3Guo W. Grant A. Novick P. J. Biol. Chem. 1999; 274: 23558-23564Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar). Sec5 may have a different in the small are of the superfamily of small G in and membrane effector for Ral Ral which the of Ral on C. A. J. Cell Sci. PubMed Google S. S. A. S. A. EMBO J. 1999; 18: PubMed Scopus Google Scholar) and interactions with the Rho S. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), an protein, and which is involved in vesicle P. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The that Ral is involved in regulation of exocytosis a secretory and exocyst was found to to A. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). of small G that is to the of the nucleotide is the effector which with The effector does not to Sec5 and has been shown to of to the basolateral in polarized epithelial S. C. Cell Biol. PubMed Scopus Google of Sec5 for Ral binding was and the S. A. Cell Biol. PubMed Scopus Google Scholar). The of Sec5 a the IPT P. Trends Sci. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), which is found in such as and and in transcription it is for A domain of this has not been found in a G protein effector and it is not to predict how it with the of the domain of the is and forms a fold C. A. A. PubMed Scopus Google S. C. A. 1999; PubMed Scopus Google Biol. PubMed Scopus Google Scholar). It is of to how the Ral of with is for protein A guanine nucleotide dissociation inhibitor for Rho an structure in complex with and has been Full Text Full Text PDF PubMed Scopus Google D. P. Biol. PubMed Scopus Google D. C. PubMed Scopus Google have the structure of the Ral-binding domain of Sec5 and that it forms an IPT We have mapped the binding of to this domain and found that the of Sec5 that with Ral is to that in other IPT domains for protein-protein this is different from that in the Rho domain for the Rho and Ral may to the IPT domain of Sec5 be and with other G and the are the Sec5 domain is to the to and of the domains is the and is a a single of a the of and which is in Sec5 and the and is and does not and is The other and the transcription factors is that is a in the in the This is in the because the from the in involved in in the transcription factors to of the from and and shown in This is in to such as the the interaction is on the of the and is of in and J. A. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The involved in are bridges are found in the are not in Sec5 are involved in is in Sec5, which is not in and is to in This is on the of the Sec5 it is it is not that Sec5 the IPT domain in a to the transcription the correlation of this determined from the of in is not which is with a protein of this Ral binding on the Sec5 IPT domain be with the of the IPT domains involved in interactions with other and shown in The IPT domain the same face to other domains the same protein S. 1999; PubMed Scopus (130) Google Scholar). and the other the same face for other IPT domains and for other domains the same protein S. PubMed Scopus Google S.C. PubMed Scopus Google PubMed Scopus Google S. Biol. PubMed Scopus Google C. A. Biol. 9: PubMed Scopus Google A. S.C. PubMed Scopus Google S.C. Full Text Full Text PDF PubMed Scopus Google S. Full Text Full Text PDF PubMed Scopus Google P. EMBO J. PubMed Google Scholar). The in IPT domains are to the protein-protein interaction but the other Ig-like domain that has been found to G that from Rho the face to the Rho Full Text Full Text PDF PubMed Scopus Google D. P. Biol. PubMed Scopus Google D. C. PubMed Scopus Google Scholar). It is not that this in binding the and Sec5, because the domain is it has of which is involved in G protein binding and the it with the G protein, the of with the that is to the of the Rho number of G complex have been and have shown that the that G G the effector effector The Sec5 domain with the effector because of of Ral interaction with Sec5 S. C. Cell Biol. PubMed Scopus Google Scholar). other G the that with the effector it is not to predict which of Sec5 may be this of for the C. A. A. PubMed Scopus Google S. C. A. 1999; PubMed Scopus Google Biol. PubMed Scopus Google Scholar) and the effector D. D. 1999; PubMed Scopus Google A. 1999; PubMed Scopus Google A. D. D. Biol. PubMed Scopus Google Scholar), an is by an interaction the of the G protein and a from the the of Sec5, it is to that a be in this effector because of the in binding to the Ral are and an is in this it a of the Sec5 IPT that is available to The that this and on Ral binding is this involved in an have to be of the Sec5 because is not and the single of in the to of the G protein other Ral effector that has been in is Ral The Ral-binding domain of this protein has been and S. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). is structure available for this protein, structure that is and that the Ral-binding domain overlaps a the interaction Ral and is to be different from that Ral and are other G the effector domain is S. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), C. 2001; PubMed Scopus Google Scholar), and C. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), but the and interactions are the IPT fold in the IPT domain of Sec5 seems to with Ral in S. cerevisiae Ral does not Sec5 the S. cerevisiae the exocyst components that to G not with to the IPT it is that Ral is the small the exocyst that an The other Ral effector Ral and not an IPT It to be other Ral are that an IPT to interaction with exocytosis is crucial to the regulation of cellular to the of regulation of exocytosis is the of small G in of the components of the exocyst We have the structure of the Ral-binding domain of the exocyst protein, This is the structure of a Ral effector domain and the G protein effector that an IPT fold to the We have shown that the Sec5 Ral-binding domain forms an IPT domain that is to to the transcription factors such as of the Ral binding site in the Sec5 domain the of IPT a is for protein-protein interactions and that this is not the same as that for with of the Ral-binding of Sec5 with the of that with Rho G that the and are A of the that Sec5 with Ral of the structure of the The be to that be to the of the interaction in exocyst assembly the plasma membrane. Spatial regulation of exocytosis is crucial for a variety of cellular processes, including embryogenesis, establishment and maintenance of cell polarity, and neuronal growth cone formation (reviewed in Ref. 1Hsu S.C. Hazuka C.D. Foletti D.L. Scheller R.H. Trends Cell Biol. 1999; 9: 150-153Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). The exocyst complex is involved in the final stage of exocytosis, when post-Golgi vesicles are targeted and dock to the plasma membrane. The exocyst consists of an assembly of eight proteins: Sec3, -5, -6, -8, -10, and 15, and Exo70 and -84, which form a complex localized to sites of vesicle docking to the plasma membrane during Saccharomyces cerevisiae the exocyst directs vectorial targeting of secretory vesicles to sites of membrane expansion, such as bud sites. It appears that Sec3p, which is always localized to the plasma membrane, forms a targeting patch and is the spatial landmark for polarized exocytosis (reviewed in Ref. 1Hsu S.C. Hazuka C.D. Foletti D.L. Scheller R.H. Trends Cell Biol. 1999; 9: 150-153Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). A subcomplex of Sec15p and Sec10p is localized to secretory vesicles (2Guo W. Roth D. Walch-Solimena C. Novick P. EMBO J. 1999; 18: 1071-1080Crossref PubMed Scopus (496) Google Scholar) and a network of protein-protein interactions among the exocyst components bridges Sec15p-Sec10p to the targeting patch made by Sec3p (3Guo W. Grant A. Novick P. J. Biol. Chem. 1999; 274: 23558-23564Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar). mammals the exocyst is involved in the targeting of Golgi-derived vesicles to the basolateral membrane of polarized epithelia. The regulation of the exocyst seems to be somewhat different in higher eukaryotes, because Sec3 does not have the same role. Rather, in polarized epithelial cells, Exo70 is localized to the plasma membrane (4Matern H.T. Yeaman C. Nelson W.J. Scheller R.H. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 9648-9653Crossref PubMed Scopus (95) Google Scholar), whereas the other components of the exocyst remain that exocyst assembly the membrane is dependent upon Sec3 as in of the superfamily are involved in the regulation of a variety of cellular processes, including nuclear and vesicle of exocytosis, it was that small a in exocyst regulation P. W. Trends Cell Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). a of Sec15p to secretory vesicles (2Guo W. Roth D. Walch-Solimena C. Novick P. EMBO J. 1999; 18: 1071-1080Crossref PubMed Scopus (496) Google Scholar). The exocyst is to the plasma membrane the interaction of Sec3p with W. Novick P. Cell Biol. 2001; PubMed Scopus Google Scholar). Sec3p has been shown to to of the Rho Novick P. W. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). it was shown that with the plasma membrane J. A. Biol. 1999; PubMed Google Scholar). The of the Rho which the in exocyst regulation a of with cells, the exocyst components not to with Rho Rather, it was recently shown that the exocyst is by S. C. Cell Biol. PubMed Scopus Google S. A. Cell Biol. PubMed Scopus Google A. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google A. Biol. PubMed Scopus Google Scholar). Ral is a small G protein that is not in S. Ral and Ral polarized exocytosis in epithelial cells, it is necessary for the to the and forms to vesicle Ral, is localized to secretory vesicles and the plasma membrane, but the exocyst component for with was found to be is the of the exocyst the subcomplex to the of the exocyst interactions with Sec3p, and (3Guo W. Grant A. Novick P. J. Biol. Chem. 1999; 274: 23558-23564Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar). Sec5 may have a different in the exocyst. Ral small are of the superfamily of small G in and membrane effector for Ral Ral which the of Ral on C. A. J. Cell Sci. PubMed Google S. S. A. S. A. EMBO J. 1999; 18: PubMed Scopus Google Scholar) and interactions with the Rho S. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), an protein, and which is involved in vesicle P. J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The that Ral is involved in regulation of exocytosis a secretory and The exocyst was found to to A. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). of small G that is to the of the nucleotide is the effector which with The effector does not to Sec5 and has been shown to of to the basolateral in polarized epithelial S. C. Cell Biol. PubMed Scopus Google Scholar). The of Sec5 for Ral binding was and the S. A. Cell Biol. PubMed Scopus Google Scholar). The of Sec5 a the IPT P. Trends Sci. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), which is found in such as and and in transcription it is for A domain of this has not been found in a G protein effector and it is not to predict how it with the of the domain of the is and forms a fold C. A. A. PubMed Scopus Google S. C. A. 1999; PubMed Scopus Google Biol. PubMed Scopus Google Scholar). It is of to how the Ral of with is for protein A guanine nucleotide dissociation inhibitor for Rho an structure in complex with and has been Full Text Full Text PDF PubMed Scopus Google D. P. Biol. PubMed Scopus Google D. C. PubMed Scopus Google Scholar). We have the structure of the Ral-binding domain of Sec5 and that it forms an IPT We have mapped the binding of to this domain and found that the of Sec5 that with Ral is to that in other IPT domains for protein-protein this is different from that in the Rho domain for the Rho and Ral may to the IPT domain of Sec5 be and with other G and the are the Sec5 domain is to the to and of the domains is the and is a a single of a the of and which is in Sec5 and the and is and does not and is The other and the transcription factors is that is a in the in the This is in the because the from the in involved in in the transcription factors to of the from and and shown in This is in to such as the the interaction is on the of the and is of in and J. A. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The involved in are bridges are found in the are not in Sec5 are involved in is in Sec5, which is not in and is to in This is on the of the Sec5 it is it is not that Sec5 the IPT domain in a to the transcription the correlation of this determined from the of in is not which is with a protein of this Ral binding on the Sec5 IPT domain be with the of the IPT domains involved in interactions with other and shown in The IPT domain the same face to other domains the same protein S. 1999; PubMed Scopus (130) Google Scholar). and the other the same face for other IPT domains and for other domains the same protein S. PubMed Scopus Google S.C. PubMed Scopus Google PubMed Scopus Google S. Biol. PubMed Scopus Google C. A. Biol. 9: PubMed Scopus Google A. S.C. PubMed Scopus Google S.C. Full Text Full Text PDF PubMed Scopus Google S. Full Text Full Text PDF PubMed Scopus Google P. EMBO J. PubMed Google Scholar). The in IPT domains are to the protein-protein interaction but the other Ig-like domain that has been found to G that from Rho the face to the Rho Full Text Full Text PDF PubMed Scopus Google D. P. Biol. PubMed Scopus Google D. C. PubMed Scopus Google Scholar). It is not that this in binding the and Sec5, because the domain is it has of which is involved in G protein binding and the it with the G protein, the of with the that is to the of the Rho number of G complex have been and have shown that the that G G the effector effector The Sec5 domain with the effector because of of Ral interaction with Sec5 S. C. Cell Biol. PubMed Scopus Google Scholar). other G the that with the effector it is not to predict which of Sec5 may be this of for the C. A. A. PubMed Scopus Google S. C. A. 1999; PubMed Scopus Google Biol. PubMed Scopus Google Scholar) and the effector D. D. 1999; PubMed Scopus Google A. 1999; PubMed Scopus Google A. D. D. Biol. PubMed Scopus Google Scholar), an is by an interaction the of the G protein and a from the the of Sec5, it is to that a be in this effector because of the in binding to the Ral are and an is in this it a of the Sec5 IPT that is available to The that this and on Ral binding is this involved in an have to be of the Sec5 because is not and the single of in the to of the G protein other Ral effector that has been in is Ral The Ral-binding domain of this protein has been and S. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). is structure available for this protein, structure that is and that the Ral-binding domain overlaps a the interaction Ral and is to be different from that Ral and are other G the effector domain is S. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), C. 2001; PubMed Scopus Google Scholar), and C. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), but the and interactions are the IPT fold in the IPT domain of Sec5 seems to with Ral in S. cerevisiae Ral does not Sec5 the S. cerevisiae the exocyst components that to G not with to the IPT it is that Ral is the small the exocyst that an The other Ral effector Ral and not an IPT It to be other Ral are that an IPT to interaction with exocytosis is crucial to the regulation of cellular to the of regulation of exocytosis is the of small G in of the components of the exocyst We have the structure of the Ral-binding domain of the exocyst protein, This is the structure of a Ral effector domain and the G protein effector that an IPT fold to the We have shown that the Sec5 Ral-binding domain forms an IPT domain that is to to the transcription factors such as of the Ral binding site in the Sec5 domain the of IPT a is for protein-protein interactions and that this is not the same as that for with of the Ral-binding of Sec5 with the of that with Rho G that the and are A of the that Sec5 with Ral of the structure of the The be to that be to the of the interaction in exocyst assembly the plasma membrane. The and the are the Sec5 domain is to the to and of the domains is the and is a a single of a the of and which is in Sec5 and the and is and does not and is The other and the transcription factors is that is a in the in the This is in the because the from the in The involved in in the transcription factors to of the from and and shown in This is in to such as the the interaction is on the of the and is of in and J. A. J. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The involved in are bridges are found in the are not in Sec5 are involved in is in Sec5, which is not in and is to in This is on the of the Sec5 it is it is not that Sec5 the IPT domain in a to the transcription the correlation of this determined from the of in is not which is with a protein of this The Ral binding on the Sec5 IPT domain be with the of the IPT domains involved in interactions with other and shown in The IPT domain the same face to other domains the same protein S. 1999; PubMed Scopus (130) Google Scholar). and the other the same face for other IPT domains and for other domains the same protein S. PubMed Scopus Google S.C. PubMed Scopus Google PubMed Scopus Google S. Biol. PubMed Scopus Google C. A. Biol. 9: PubMed Scopus Google A. S.C. PubMed Scopus Google S.C. Full Text Full Text PDF PubMed Scopus Google S. Full Text Full Text PDF PubMed Scopus Google P. EMBO J. PubMed Google Scholar). The in IPT domains are to the protein-protein interaction but the other Ig-like domain that has been found to G that from Rho the face to the Rho Full Text Full Text PDF PubMed Scopus Google D. P. Biol. PubMed Scopus Google D. C. PubMed Scopus Google Scholar). It is not that this in binding the and Sec5, because the domain is it has of which is involved in G protein binding and the it with the G protein, the of with the that is to the of the Rho A number of G complex have been and have shown that the that G G the effector effector The Sec5 domain with the effector because of of Ral interaction with Sec5 S. C. Cell Biol. PubMed Scopus Google Scholar). other G the that with the effector it is not to predict which of Sec5 may be this of for the C. A. A. PubMed Scopus Google S. C. A. 1999; PubMed Scopus Google Biol. PubMed Scopus Google Scholar) and the effector D. D. 1999; PubMed Scopus Google A. 1999; PubMed Scopus Google A. D. D. Biol. PubMed Scopus Google Scholar), an is by an interaction the of the G protein and a from the the of Sec5, it is to that a be in this effector because of the in binding to the Ral are and an is in this it a of the Sec5 IPT that is available to The that this and on Ral binding is this involved in an have to be of the Sec5 because is not and the single of in the to of the G protein The other Ral effector that has been in is Ral The Ral-binding domain of this protein has been and S. A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). is structure available for this protein, structure that is and that the Ral-binding domain overlaps a the interaction Ral and is to be different from that Ral and are other G the effector domain is S. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), C. 2001; PubMed Scopus Google Scholar), and C. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), but the and interactions are the IPT fold in the IPT domain of Sec5 seems to with Ral in S. cerevisiae Ral does not Sec5 the S. cerevisiae the exocyst components that to G not with to the IPT it is that Ral is the small the exocyst that an The other Ral effector Ral and not an IPT It to be other Ral are that an IPT to interaction with exocytosis is crucial to the regulation of cellular to the of regulation of exocytosis is the of small G in of the components of the exocyst We have the structure of the Ral-binding domain of the exocyst protein, This is the structure of a Ral effector domain and the G protein effector that an IPT fold to the We have shown that the Sec5 Ral-binding domain forms an IPT domain that is to to the transcription factors such as of the Ral binding site in the Sec5 domain the of IPT a is for protein-protein interactions and that this is not the same as that for with of the Ral-binding of Sec5 with the of that with Rho G that the and are A of the that Sec5 with Ral of the structure of the The be to that be to the of the interaction in exocyst assembly the plasma membrane. We for and