RESUMO
Cyclic nucleotide-sensitive ion channels, known as HCN and CNG channels, are crucial in neuronal excitability and signal transduction of sensory cells. HCN and CNG channels are activated by binding of cyclic nucleotides to their intracellular cyclic nucleotide-binding domain (CNBD). However, the mechanism by which the binding of cyclic nucleotides opens these channels is not well understood. Here, we report the solution structure of the isolated CNBD of a cyclic nucleotide-sensitive K(+) channel from Mesorhizobium loti. The protein consists of a wide anti-parallel beta-roll topped by a helical bundle comprising five alpha-helices and a short 3(10)-helix. In contrast to the dimeric arrangement ('dimer-of-dimers') in the crystal structure, the solution structure clearly shows a monomeric fold. The monomeric structure of the CNBD supports the hypothesis that the CNBDs transmit the binding signal to the channel pore independently of each other.
Assuntos
Alphaproteobacteria/química , AMP Cíclico/química , Canais de Cátion Regulados por Nucleotídeos Cíclicos/química , Canais de Potássio/química , Cristalografia por Raios X , AMP Cíclico/metabolismo , Canais de Cátion Regulados por Nucleotídeos Cíclicos/metabolismo , Modelos Moleculares , Canais de Potássio/metabolismo , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , SoluçõesRESUMO
Ion channels gated by cyclic nucleotides have crucial roles in neuronal excitability and signal transduction of sensory neurons. Here, we studied ligand binding of a cyclic nucleotide-activated K(+) channel from Mesorhizobium loti and its isolated cyclic nucleotide-binding domain. The channel and the binding domain alone bind cyclic AMP with similar affinity in a non-cooperative manner. The cAMP sensitivities of binding and activation coincide. Thus, each subunit in the tetrameric channel acts independently of the others. The binding and gating properties of the bacterial channel are distinctively different from those of eukaryotic cyclic nucleotide-gated channels.
Assuntos
Alphaproteobacteria/metabolismo , Proteínas de Bactérias/química , AMP Cíclico/química , Canais de Cátion Regulados por Nucleotídeos Cíclicos/química , Canais de Potássio/química , Proteínas de Bactérias/genética , Canais de Cátion Regulados por Nucleotídeos Cíclicos/genética , Ligantes , Canais de Potássio/genética , Estrutura Terciária de Proteína , Subunidades Proteicas/química , Espectrometria de FluorescênciaRESUMO
In order to determine the structure of the 15 kDa cyclic nucleotide binding domain of a cyclic nucleotide-activated K(+) channel from Mesorhizobium loti and its interaction with cAMP, nearly complete (1)H, (13)C, and (15)N chemical shifts were assigned.