Suramin analogues as subtype-selective G protein inhibitors.
G protein alpha subunits expose specific binding sites that allow for the sequential, conformation-dependent binding of protein reaction partners, e.g., G protein beta gamma dimers, receptors, and effectors. These domains represent potential sites for binding of low-molecular-weight inhibitors. We tested the following suramin analogues as G protein antagonists: 8-(3-nitrobenzamido)-1,3,5-naphtalenetrisulfonic acid (NF007), 8-(3-(3-nitrobenzamido)benzamido)-1,3,5-naphtalenetrisulfonic++  + acid NF018), 8,8'-(carbonylbis(imino-3,1-phenylene))bis-(1,3,5-naphtalenetri  sulfonic acid) (NF023), 8,8'-(carbonylbis(imino-3,1-phenylene)carbonylimino-(3,1-phe nylene))bis-(1,3, 5-naphtalenetrisulfonic acid) (NF037), and suramin. The compounds suppressed [35S]GTPgammaS binding to purified, recombinant G protein alpha subunits, an effect that is due to inhibition of GDP release. Suramin is selective for recombinant Gsalpha-s (EC50 values o f approximately 240 nM; rank order of potency, suramin > NF037 > NF023 > NF018 > NF007), whereas NF023 is selective for recombinant Gi alpha-1 and recombinant Go alpha (EC50 value of approximately 300 nM; rank order of potency, NF023 > / = NF037 > suramin >0 NF018 > NF007). Selectivity was also demonstrated on a cellular level. In rat sympathetic neurons, alpha-2-adrenergic and muscarinic receptor-dependent inhibition of the voltage-sensitive calcium current is mediated by Gi/Go, whereas inhibition by vasoactive intestinal peptide (VIP) is mediated by Gs. Calcium current inhibition by alpha2-adrenergic and muscarinic receptors was greatly reduced when 100 microM NF023 was applied intracellularly, whereas the response to VIP was unaffected; in contrast, the response to VIP was blunted only with 100 microM suramin in the recording pipette. The suramin analogues do not interfere with the interaction between alpha subunits and G protein beta gamma dimer but compete with binding of the effector. The addition of purified adenylyl cyclase reverses the inhibitory effect of suramin on the rate of [35S]GTPgammaS binding to recombinant Gsalpha-s, indicating direct competition for a common site; similarly, immunoprecipitation by an antibody directed against an epitope of the effector binding site is inhibited by suramin. Our results show that it is possible to design G protein inhibitors that target the effector binding site on the alpha subunits.
Freissmuth
M
M
Institute of Pharmacology, Vienna University, Austria.
Boehm
S
S
Beindl
W
W
Nickel
P
P
Ijzerman
A P
AP
Hohenegger
M
M
Nanoff
C
C
D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D051381:Rats; D017207:Rats, Sprague-Dawley; D013498:Suramin / Q000031:analogs & derivatives / Q000494:pharmacology*
D015220:Calcium Channels; D004791:Enzyme Inhibitors; C105374:NF023; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013498:Suramin; D019204:GTP-Binding Proteins