TY - JOUR
T1 - Differential interactions of the catalytic subunits of adenylyl cyclase with forskolin analogs
AU - Pinto, Cibele
AU - Hübner, Melanie
AU - Gille, Andreas
AU - Richter, Mark
AU - Mou, Tung Chung
AU - Sprang, Stephen R.
AU - Seifert, Roland
N1 - Funding Information:
This work was supported by Deutsche Forschungsgemeinschaft research grant Se 529/5-1 to R.S, NIH grant RO1 DK 46371 to S.R.S. and a predoctoral fellowship from the Elite Graduate Student Program of Free State of Bavaria to M.H. We also thank the reviewers of this paper for their constructive critique.
PY - 2009/7/1
Y1 - 2009/7/1
N2 - The diterpene forskolin (FS) binds to, and activates, mammalian membranous adenylyl cyclase (AC) isoforms I-VIII. Diterpenes without C1-OH group do not activate ACs. The C1-OH group forms a hydrogen bond with the backbone oxygen of Val506 of the C1 catalytic subunit of AC (isoform V numbering). To better understand the mechanism of AC activation we examined the interactions of FS and eight FS analogs with purified catalytic AC subunits C1 (AC V) and C2 (AC II) by fluorescence spectroscopy, using 2′,3′-O-(N-methylanthraniloyl)-guanosine 5′-triphosphate (MANT-GTP) as fluorescent reporter probe, and by enzymatic activity. FS analogs induced C1/C2 assembly as assessed by fluorescence resonance energy transfer from Trp1020 of C2 to MANT-GTP and by increased direct MANT-GTP fluorescence in the order of efficacy FS ∼ 7-deacetyl-FS ∼ 6-acetyl-7-deacetyl-FS ∼ 9-deoxy-FS > 7-deacetyl-7-(N-methylpiperazino-γ-butyryloxy)-FS > 1-deoxy-FS ∼ 1,9-dideoxy-FS ∼ 7-deacetyl-1-deoxy-FS ∼ 7-deacetyl-1,9-dideoxy-FS. In contrast, FS analogs activated catalysis in the order of efficacy FS > 7-deacety-FS ∼ 6-acetyl-7-deacetyl-FS ∼ 9-deoxy-FS > 7-deacetyl-7-(N-methylpiperazino-γ-butyryloxy)-FS ≫ 1-deoxy-FS, 1,9-dideoxy-FS, 7-deacetyl-1-deoxy-FS and 7-deacetyl-1,9-dideoxy-FS (all ineffective). 1-Deoxy-FS analogs inhibited FS-stimulated catalysis by an apparently non-competitive mechanism. Our data suggest a two-step mechanism of AC activation by diterpenes. In the first step, diterpenes, regardless of their substitution pattern, promote C1/C2 assembly. In the second and yet poorly understood step, diterpenes that form a hydrogen bond between C1-OH and Val506 promote a conformational switch that results in activation of catalysis. The apparent non-competitive interaction of FS with 1-deoxy-FS analogs is explained by impaired ligand exchange due to strong hydrophobic interactions with C1/C2.
AB - The diterpene forskolin (FS) binds to, and activates, mammalian membranous adenylyl cyclase (AC) isoforms I-VIII. Diterpenes without C1-OH group do not activate ACs. The C1-OH group forms a hydrogen bond with the backbone oxygen of Val506 of the C1 catalytic subunit of AC (isoform V numbering). To better understand the mechanism of AC activation we examined the interactions of FS and eight FS analogs with purified catalytic AC subunits C1 (AC V) and C2 (AC II) by fluorescence spectroscopy, using 2′,3′-O-(N-methylanthraniloyl)-guanosine 5′-triphosphate (MANT-GTP) as fluorescent reporter probe, and by enzymatic activity. FS analogs induced C1/C2 assembly as assessed by fluorescence resonance energy transfer from Trp1020 of C2 to MANT-GTP and by increased direct MANT-GTP fluorescence in the order of efficacy FS ∼ 7-deacetyl-FS ∼ 6-acetyl-7-deacetyl-FS ∼ 9-deoxy-FS > 7-deacetyl-7-(N-methylpiperazino-γ-butyryloxy)-FS > 1-deoxy-FS ∼ 1,9-dideoxy-FS ∼ 7-deacetyl-1-deoxy-FS ∼ 7-deacetyl-1,9-dideoxy-FS. In contrast, FS analogs activated catalysis in the order of efficacy FS > 7-deacety-FS ∼ 6-acetyl-7-deacetyl-FS ∼ 9-deoxy-FS > 7-deacetyl-7-(N-methylpiperazino-γ-butyryloxy)-FS ≫ 1-deoxy-FS, 1,9-dideoxy-FS, 7-deacetyl-1-deoxy-FS and 7-deacetyl-1,9-dideoxy-FS (all ineffective). 1-Deoxy-FS analogs inhibited FS-stimulated catalysis by an apparently non-competitive mechanism. Our data suggest a two-step mechanism of AC activation by diterpenes. In the first step, diterpenes, regardless of their substitution pattern, promote C1/C2 assembly. In the second and yet poorly understood step, diterpenes that form a hydrogen bond between C1-OH and Val506 promote a conformational switch that results in activation of catalysis. The apparent non-competitive interaction of FS with 1-deoxy-FS analogs is explained by impaired ligand exchange due to strong hydrophobic interactions with C1/C2.
KW - Adenylyl cyclase
KW - Diterpenes
KW - Fluorescence spectroscopy
KW - Forskolin
KW - MANT-GTP
UR - http://www.scopus.com/inward/record.url?scp=67349241188&partnerID=8YFLogxK
U2 - 10.1016/j.bcp.2009.03.023
DO - 10.1016/j.bcp.2009.03.023
M3 - Article
C2 - 19447224
AN - SCOPUS:67349241188
SN - 0006-2952
VL - 78
SP - 62
EP - 69
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 1
ER -