An Important Functional Role of the N Terminus Domain of Type VI Adenylyl Cyclase in Gαi-mediated Inhibition

We show herein that removal of the first 86 amino acids (aa) of the N terminus (designated N) of type VI adenylyl cyclase (ACVI) caused the resultant ACVI mutant (ACVI-ΔA87) to be more greatly inhibited by a Gαi-coupled receptor or activated Gαi protein. Moreover, invitro binding of the full-length N and C1a domain (designated C1a), which interacts with Gαi, was detected. A truncated N terminus (aa 1–86) also interacted with C1a, suggesting that the C1a-interacting region is located within aa 1–86. Mutation analyses further revealed that N might interact with C1a in the region (aa 434–505) where Gαi is bound. Mutations of two residues (Leu-472 and Val-476) located in this N-binding region of C1a suppressed the interaction between recombinant N and C1a and markedly reduced Gαi-mediated inhibition of ACVI-ΔA87. Further biochemical analyses of the effect of internal mutations of Leu-472/Val-476 on Gαi-mediated inhibition of wild-type ACVI and ACVI-ΔA87 suggested that N modulates the Gαi-mediated inhibition of ACVI via binding to C1a when the level of Gαi is low (i.e. around the IC50 value) and that a more complicated interfering mode results when the level of Gαi is high (i.e. ∼10- to 20-fold of the IC50 value). Collectively, data presented herein suggest a novel function of the N terminus of ACVI in Gαi-mediated regulation. We show herein that removal of the first 86 amino acids (aa) of the N terminus (designated N) of type VI adenylyl cyclase (ACVI) caused the resultant ACVI mutant (ACVI-ΔA87) to be more greatly inhibited by a Gαi-coupled receptor or activated Gαi protein. Moreover, invitro binding of the full-length N and C1a domain (designated C1a), which interacts with Gαi, was detected. A truncated N terminus (aa 1–86) also interacted with C1a, suggesting that the C1a-interacting region is located within aa 1–86. Mutation analyses further revealed that N might interact with C1a in the region (aa 434–505) where Gαi is bound. Mutations of two residues (Leu-472 and Val-476) located in this N-binding region of C1a suppressed the interaction between recombinant N and C1a and markedly reduced Gαi-mediated inhibition of ACVI-ΔA87. Further biochemical analyses of the effect of internal mutations of Leu-472/Val-476 on Gαi-mediated inhibition of wild-type ACVI and ACVI-ΔA87 suggested that N modulates the Gαi-mediated inhibition of ACVI via binding to C1a when the level of Gαi is low (i.e. around the IC50 value) and that a more complicated interfering mode results when the level of Gαi is high (i.e. ∼10- to 20-fold of the IC50 value). Collectively, data presented herein suggest a novel function of the N terminus of ACVI in Gαi-mediated regulation. The mammalian adenylyl cyclase (AC) 1The abbreviations used are: AC, adenylyl cyclase; ACVI, type VI adenylyl cyclase; PKC, protein kinase C; PBS, phosphate-buffered saline; H6, hexahistidine; GTPγS, guanosine 5′-O-(thiotriphosphate); aa, amino acid(s); D2s-R, dopamine D2 receptor; CHOP, Chinese hamster ovary cell expressing the polyoma large T antigen; Ni-NTA, nickel-nitrilotriacetic acid; DTT, dithiothreitol; Quin, quinpirole; GPCR, G protein-coupled receptor. superfamily consists of nine membrane-bound isoforms. All of these possess three large cytosolic domains (designated N, C1a, and C2 domains; Fig. 1A), which are separated by two sets of six-transmembrane domains (1Sunahara R.K. Dessauer C.W. Gilman A.G. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 461-480Crossref PubMed Scopus (744) Google Scholar, 2Patel T.B. Du Z. Pierre S. Cartin L. Scholich K. Gene (Amst.). 2001; 269: 13-25Crossref PubMed Scopus (143) Google Scholar, 3Chern Y. Cell. Signal. 2000; 12: 195-204Crossref PubMed Scopus (72) Google Scholar). The C1a and C2 domains among the nine AC members are highly homologous (with 50–90% similarity in amino acids). In addition, the C1a and C2 domains of each AC share ∼50% similarity and form the catalytic core complex, which can be stimulated by forskolin or Gαs proteins (4Sunahara R.K. Dessauer C.W. Whisnant R.E. Kleuss C. Gilman A.G. J. Biol. Chem. 1997; 272: 22265-22271Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar, 5Dessauer C.W. Scully T.T. Gilman A.G. J. Biol. Chem. 1997; 272: 22272-22277Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar, 6Dessauer C.W. Gilman A.G. J. Biol. Chem. 1997; 272: 27787-27795Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). Crystallographic analysis of the catalytic complex consisting of the C1a domain, the C2 domain, and the GTPγS-bound Gαs protein revealed that forskolin and/or Gαs stimulate ACs by enhancing the interaction between the C1a and C2 domains and by stabilizing the C1a-C2 catalytic core complex (7Tesmer J.J. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (680) Google Scholar). Although most ACs can be activated by Gαs and forskolin, regulation of each AC isozyme differs. Studies of the more-variable N and C1b domains reveal that these two domains may play important regulatory roles. For example, the C1b domain has been implicated in the regulation of AC isozymes mediated by Ca2+/calmodulin, calcineurin, or protein kinase A (8Levin L.R. Reed R.R. J. Biol. Chem. 1995; 270: 7573-7579Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, 9Cali J.J. Parekh R.S. Krupinski J. J. Biol. 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Others and we have shown that another variable region, the N-terminal domain, also significantly contributes to the regulation of AC activity (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google Scholar, 15Gu C. Cooper D.M. J. Biol. Chem. 1999; 274: 8012-8021Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). Specifically, the N-terminal domain of ACVI (amino acids 1–160) plays an important role in the protein kinase C (PKC)-mediated inhibition and phosphorylation of ACVI (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google Scholar). Removal of the first 86 amino acids (aa) of ACVI reduced the inhibitory effect of PKC on ACVI activity without affecting the basic enzymatic properties, including the affinities toward its substrate and two stimuli (forskolin and Gαs protein (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google Scholar)). The N-terminal domain of ACVI therefore functions as a regulatory domain. Further biochemical analyses revealed that PKC phosphorylation and located in the three large cytosolic domains of ACVI, significantly to inhibition of ACVI T.H. H.L. Kao Y.Y. Hwang M.J. Chern Y. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (37) Google Scholar). among the N, and C2 domains of ACVI therefore to be important regulation of ACVI Gαi-mediated inhibition is a regulatory of the AC AC and ACVI can be inhibited by Gαi proteins R. J.A. Gilman A.G. Science. PubMed Scopus Google Scholar, R. Tang W.J. Gilman A.G. J. Biol. Chem. 269: Full Text PDF PubMed Google Scholar). on results an in binding the C1a domain was shown to Gαi proteins and form complexes C.W. J.J. Sprang S.R. Gilman A.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, C. Scholich K. Y. Patel T.B. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar). of full-length ACV in the and of the C1a domain revealed residues important the inhibition by Gαi was that Gαi may its inhibitory effect binding to the C1a domain the the on the C2 domain reduced interaction between the and C2 domains C.W. Chen J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In the we to suggest that the N-terminal domain of ACVI interacts with the C1a domain and may play an important role in the regulation of ACVI by Gαi was and and and cell which the polyoma large T was a Chinese hamster ovary cell and was a J. PubMed Scopus Google Scholar). in with and in and The of ACVI was by R. Iyengar of of Chen J. Iyengar R. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). of ACVI an or of ACVI in was by the The of the form dopamine D2 receptor Chen D.M. Kao Chen H.L. Chern Y. J. 1999; PubMed Scopus Google was by Chen For with the the PubMed Scopus (71) Google Scholar). and separated on to the of PubMed Scopus Google Scholar). For to that with in phosphate-buffered and with the The was aa C2 of ACVI H.L. T.H. Lin Chern Y. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). a was used the recombinant proteins R.J. Gilman A.G. J. Biol. Chem. Full Text PDF PubMed Google as analyses an a the with and three with The a activity was as Y. H.L. Y. Mol. Pharmacol. Google Scholar). a a of a of The was to the the AC activity was in a of and of protein. by the of of The was by and by The activity was to with proteins to The ACVI activity was as the between the cyclase in the with the ACVI an For expressing wild-type ACVI, cyclase of the The of ACVI activity in might have to the of the of AC regulation was among Gαs and Gαi of the Gαs protein was a Tang of The Gαs protein was in and was as S.Z. R.K. Tang W.J. Mol. Pharmacol. PubMed Scopus Google Scholar). stimulate AC the of Gαs protein was activated by in a and The of the Gαi protein was by an full-length the the of a The Gαi protein with an to its N terminus was in a R.J. Gilman A.G. J. Biol. Chem. Full Text PDF PubMed Google and was as Gilman A.G. PubMed Scopus Google Scholar). The of was a of of AC the of Gαi protein was activated by in the of and was by with a DTT, and and of the C1a and N domains of ACVI the was in a of the of each a and of of The to domains of ACVI Chen J. Iyengar R. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google are in the of The to the C terminus of the in the and or the a and in used by The mutant was by a as L.R. Gene (Amst.). PubMed Scopus Google with the and with as the The resultant which aa of ACVI, mutations and The was the the Mutations of and by The resultant was with and and the to the mutant The of the mutant protein was by a the of The mutant was by the the residues and the The mutant was also by the two and and Chen J. Iyengar R. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google as the and two and and as the The ACV was a R. The resultant a the aa of ACV to aa of was with and and the was with and and the to the In recombinant domains of ACVI in by the the was by In binding by the the recombinant proteins in of DTT, The complex was the N terminus of ACVI H.L. Chern Y. PubMed Scopus Google or and by For the interaction between Gαi and the C1a domain, recombinant protein as was first to the the and with the the proteins in of binding and The complexes on the with and three and with of the The complexes on the The of which proteins to and of the analysis The of the which proteins and as important regulation ACVI, which can be two AC isozymes and is the inhibition mediated by Gαi proteins R. J.A. Gilman A.G. Science. PubMed Scopus Google Scholar, R. Tang W.J. Gilman A.G. J. Biol. Chem. 269: Full Text PDF PubMed Google Scholar). the N-terminal domain is highly variable among AC we to the role of the N-terminal domain of ACVI in Gαi-mediated The wild-type ACVI or an N ACVI which the first aa and a in the analysis Fig. (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google was with a Gαi-coupled form D2 dopamine receptor in AC in the of forskolin the of a shown in Fig. inhibition of ACVI-ΔA87 by was more that of wild-type ACVI high of that of the N-terminal domain might ACVI to be more to Gαi-mediated this we the inhibitory effect of recombinant Gαi protein on the Gαs-evoked of wild-type ACVI and ACVI-ΔA87. of the recombinant protein in the of R.J. Gilman A.G. J. Biol. Chem. Full Text PDF PubMed Google was by its in when with of the proteins in the of with the inhibition of ACVI-ΔA87 by the Gαi was more that of wild-type ACVI in the IC50 of the Gαi the wild-type and ACVI-ΔA87 was and the of inhibition of ACVI-ΔA87 by the Gαi was markedly that of wild-type ACVI and ACVI-ΔA87 and the wild-type ACVI, further a role of the N-terminal domain of ACVI in of the N terminus of ACVI in the regulation of Gαi-mediated recombinant proteins in the or of R.J. Gilman A.G. J. Biol. Chem. Full Text PDF PubMed Google in to on a by analyses an as The and the and with or ACVI-ΔA87 used the AC activity AC activity by the activated Gαs protein was in the of recombinant protein are the as of Gαs-evoked ACVI activity in the of wild-type ACVI and and the of between the inhibition of Gαs-evoked AC of and of ACVI-ΔA87 are with the We the N-terminal domain of ACVI by that of type adenylyl cyclase the isozyme to ACVI in the AC the N-terminal domain, the C1a and C2 domains of ACV and ACVI are highly homologous Chen J. Iyengar R. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). a we the N terminus (aa 1–160) of ACVI with the N terminus (aa of The resultant mutant (designated a that of wild-type ACVI of the N terminus In with (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google which suggested that the N terminus of ACVI to the catalytic core complex, enzymatic (i.e. and of forskolin and Gαs of to of wild-type ACVI In when with in inhibition of was low and high of a Fig. of the N terminus domain markedly its to Gαi-mediated inhibition of ACVI, these results that the N terminus of ACVI plays an important role in Gαi-mediated of ACVI in a Dessauer and C.W. J.J. Sprang S.R. Gilman A.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google that the Gαi protein interacts with the C1a domain of is therefore that the N terminus of ACVI might modulate Gαi-mediated inhibition by interacting with the C1a domain. We first a C1a domain of ACVI (aa which the Gαi binding domain on a of ACV C.W. J.J. Sprang S.R. Gilman A.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google an in shown in Fig. interaction between and the Gαi which an was by an the C1a domain of ACVI, to to the Gαi protein. Moreover, recombinant C1a domains this in to the We the in binding analyses of the recombinant N (aa and the domain. an that interacts with the N-terminal domain of ACVI H.L. Chern Y. PubMed Scopus Google the be with that a protein in the in we therefore another C1a domain (aa on a of ACV (7Tesmer J.J. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (680) Google Scholar). The protein the domain of ACVI as the protein and an to its N shown in Fig. was and also be with as The to the interaction between the N and C1a domains in that and proteins be by The protein therefore was used in the the interaction region on the N terminus with the C1a domain, a truncated N-terminal domain (aa was the in binding shown in Fig. was also with the recombinant domain as was the the of the protein in the was with and The C1a-interacting region of the N terminus might therefore in the region aa 1–86. We further to where on the C1a domain the N-terminal domain recombinant proteins of the protein (aa and and in shown in Fig. the protein three of these recombinant C1a proteins The region (aa 434–505) of these three recombinant C1a proteins to the the binding of the N-terminal domain. on the of the catalytic complex of ACs (7Tesmer J.J. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (680) Google we a of the catalytic core of the C1a and C2 domains of ACVI Dessauer and C.W. J.J. Sprang S.R. Gilman A.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google that Gαi to the C1a domain the by the and Mutations of residues located in these two caused a in the between Gαi and results that the N terminus binding region of the C1a domain (aa 434–505) the which is located on the of the catalytic core complex is to the N-terminal domain of analysis with ACV suggested that two residues (Leu-472 and Val-476) in the of the C1a domain of ACVI might be important interaction with the Gαi protein Fig. and on the might also be important the interaction of the N and C1a we a recombinant mutant mutations and (designated by interact with the N terminus as the recombinant wild-type protein and located in the of the C1a domain of ACVI might play a role in the interaction with the N-terminal domain. and important interacting with the Gαi we and in the full-length ACVI and the N ACVI mutant The resultant (designated and to regulation by the N terminus which the C1a domain binding to the N the Leu-472/Val-476 markedly reduced the inhibition by Gαi Fig. an N the effect of the Leu-472/Val-476 Fig. on Gαi or effect low and to of the IC50 of and high and ∼10- to 20-fold of the IC50 of In of the N terminus the inhibition of low Gαi on a mutant which a and been as the of Gαi inhibition ACVI Fig. In the we the of the N-terminal domain of ACVI to Gαi-mediated inhibition by the effect of Gαi-mediated regulation on ACVI of a truncated N terminus and/or amino mutations of the C1a domain its and and the in interaction of the recombinant N terminus and the C1a domain with which the Gαi protein analyses revealed that the of aa a of ACVI, which the resultant mutant to be more inhibited by a Gαi-coupled receptor Fig. or the recombinant Gαi protein the full-length N terminus domain of ACVI with that of ACV also markedly the inhibition by without affecting enzymatic of ACVI and In binding that the N domain its catalytic core complex the C1a domain. In addition, the interacting located on the N and C1a domains aa and and suggested that this N region on the C1a domain of the region (aa is important to that the C1a-interacting region (aa 1–86) of the N terminus by the in binding is with the that the mutant (ACVI-ΔA87) was more to Gαi-mediated to the of the on the C1a domain. of two residues (Leu-472 and Val-476) reduced the inhibition of the ACVI (ACVI-ΔA87) by Gαi and markedly the binding of the N terminus to the C1a domain two residues play an important role in Gαi-mediated inhibition in the of an N terminus and also as a of the binding between the N and C1a Mutations of and in the full-length ACVI might on Gαi-mediated mutations of a and of the N and C1a domains to the to be more to In with this we in Gαi-mediated inhibition of the between and ACVI low (i.e. around the IC50 value) of Gαi proteins of the N terminus the of the C1a domain, which been by the mutations of and with the low of Gαi, the Gαi inhibition of type (ACVI) was significantly reduced by the of the N domain (ACVI-ΔA87) was by the Leu-472/Val-476 we that binding of N to C1a to inhibition of ACVI by low of The N terminus domain also plays a role in Gαi-mediated inhibition high of Gαi, its removal the inhibition of the full-length mutant The an of the N terminus high of Gαi (i.e. ∼10- to 20-fold of the IC50 value) is interaction of N and C1a domains was with the mutations Leu-472/Val-476 as by the N and C1a domains in to be In the of the binding of N terminus to C1a, of the N terminus the to Gαi-mediated inhibition high of Gαi, suggesting that binding to C1a might be to the N terminus suppressed the inhibition of ACVI by high of is that the N terminus might interact with an that on the C1a domain. the in the might be to We the that a interaction between N and C1a domains in and the of the of the C1a domain high of Collectively, data presented herein suggest a novel function of the N terminus of ACVI in Gαi-mediated regulation. of the of the N terminus was mediated by binding to the of the C1a domain, which might the of the by the and of the C1a domain to Gαi low of Gαi protein. The N-terminal domains of AC isozymes are highly variable and are regulatory For example, the N-terminal domain of has been implicated in binding and the activation of C. Cooper D.M. J. Biol. Chem. 1999; 274: 8012-8021Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). We that the N terminus of ACVI is inhibition (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google Scholar, T.H. H.L. Kao Y.Y. Hwang M.J. Chern Y. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (37) Google Scholar). Removal of the (aa 1–86) of ACVI its enzymatic (14Lai H.L. Lin T.H. Kao Y.Y. Lin W.J. Hwang M.J. Chern Y. Mol. Pharmacol. 1999; 56: 644-650Crossref PubMed Scopus (39) Google Scholar). In as in the of this region markedly the regulation mediated by Gαi and The N-terminal domain of ACV a effect on the enzymatic or on regulatory as the inhibition mediated by Gαi or (12Scholich K. Barbier A.J. Mullenix J.B. Patel T.B. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 2915-2920Crossref PubMed Scopus (64) Google Scholar, C. Cooper D.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (39) Google Scholar)). of the N terminus of ACVI with that of ACV the enzymatic of ACVI markedly the inhibition mediated by further in to its in the N terminus of ACVI might also play a role in Gαi-mediated that of the N terminus of ACVI with an domain can be to its function (i.e. Gαi-mediated the enhancing effect as that in the ACVI mutant Fig. a is that the N terminus of ACV is that of ACVI and might a the on the C1a domain and the inhibition by has been shown that Gαi-coupled to Gαi proteins and to of inhibition of AC Y. Y. A. A. S. A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. Y. A. PubMed Scopus Google Scholar, G. K. K. Smit M.J. R. Mol. Pharmacol. 2001; PubMed Scopus Google Scholar). In to by Gαi protein might AC For example, the dopamine receptor significantly the activity of ACV that of ACVI, which to the as the the of inhibition are ACV and ACVI Mol. Pharmacol. 1997; PubMed Scopus (118) Google Scholar). The is suggested by is that the of Gαi protein on ACVI and ACV may of might in Gαi to regulation of AC the and catalytic core complexes of AC isozymes are in N-terminal the that the N terminus of AC isozymes might to Gαi by the on the catalytic core The of its N terminus and the catalytic complex ACVI with a regulatory mode Gαi-mediated in the data presented herein is that the in inhibition between ACVI-ΔA87 and the wild-type ACVI was more when the was stimulated by Gαs by forskolin a might have the that Gαi proteins are more in AC activity AC activity as R. Tang W.J. Gilman A.G. J. Biol. Chem. 269: Full Text PDF PubMed Google Scholar). this might have been caused by the of Specifically, in two cell the has been shown to ACs J. Biol. Chem. 269: Full Text PDF PubMed Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The Gαi by the in to the inhibition of ACVI therefore might be is that the regulatory mode of ACVI by might by Gαi which to the of N terminus of ACVI as in Fig. The the regulation of ACVI by Gαi has been on a analysis of ACV C.W. J.J. Sprang S.R. Gilman A.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google the basic region of ACVI might in the by the and of the C1a domain. analyses and revealed that the N terminus might interact with C1a the In addition, mutations of and located in the caused including a in Gαi-mediated inhibition in the of an N terminus and of the N and C1a domains two residues (Leu-472 and Val-476) to be important the interaction between the C1a and N and between the C1a domain and the binding on the C1a domain the N and Gαi might the in the Gαi-mediated inhibition between wild-type ACVI and the N ACVI (ACVI-ΔA87) be by the of the D2 or the Gαi and of the N terminus to the C1a domain to the inhibition by low of Gαi in a We to further the binding of the N terminus domain and Gαi to the C1a domain in to the low and of the recombinant N terminus protein analyses that the C1a-interacting region (aa 1–86) on the N terminus is to be Sci. Full Text Full Text PDF PubMed Scopus Google Scholar). The highly of the N terminus also that is to form a complex with the C1a to its to be the interaction between the N and the C1a domains can be is that the N terminus of ACVI might play a role and the catalytic core complex which to of the Gαi protein to its interacting on the C1a domain. of an of an by its regulatory domain has including protein kinase C of PKC a that to of the kinase domain by its regulatory domain in the Y. J. PubMed Scopus Google Scholar). In we to that the N terminus of ACVI interacts with its catalytic core and plays an important role in the regulation of Gαi-mediated further the role of the N-terminal domain to the of the AC superfamily and to the of Gαi-mediated We of of and on the of recombinant proteins and Chen of of by We are also to the the and Fig. and Chen and