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  • Prolyl isomerization controls activation kinetics of a cyclic nucleotide-gated ion channel.

Prolyl isomerization controls activation kinetics of a cyclic nucleotide-gated ion channel.

Nature communications (2020-12-18)
Philipp A M Schmidpeter, Jan Rheinberger, Crina M Nimigean
ABSTRACT

SthK, a cyclic nucleotide-modulated ion channel from Spirochaeta thermophila, activates slowly upon cAMP increase. This is reminiscent of the slow, cAMP-induced activation reported for the hyperpolarization-activated and cyclic nucleotide-gated channel HCN2 in the family of so-called pacemaker channels. Here, we investigate slow cAMP-induced activation in purified SthK channels using stopped-flow assays, mutagenesis, enzymatic catalysis and inhibition assays revealing that the cis/trans conformation of a conserved proline in the cyclic nucleotide-binding domain determines the activation kinetics of SthK. We propose that SthK exists in two forms: trans Pro300 SthK with high ligand binding affinity and fast activation, and cis Pro300 SthK with low affinity and slow activation. Following channel activation, the cis/trans equilibrium, catalyzed by prolyl isomerases, is shifted towards trans, while steady-state channel activity is unaffected. Our results reveal prolyl isomerization as a regulatory mechanism for SthK, and potentially eukaryotic HCN channels. This mechanism could contribute to electrical rhythmicity in cells.

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8-Aminonaphthalene-1,3,6-trisulfonic acid disodium salt, BioReagent, suitable for fluorescence, ≥90% (CE)