Functional characterization and optimization of a bacterial cyclic nucleotide-gated channel

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• Cyclic nucleotide-gated (CNG) channels are essential for sensory transduction in vision and olfaction.
• Direct cyclic nucleotide binding (cAMP/cGMP) triggers channel opening, but the precise gating mechanism remains unclear.
• Bacterial SthK channels offer a model system for studying CNG channel gating, but native limitations hinder research.

Purpose of the Study:

• To characterize SthK channel gating in a bacterial membrane environment.
• To address SthK toxicity and improve its utility as a model for structure-function studies.
• To elucidate the gating mechanism of CNG channels.

Main Methods:

• Expression of SthK in giant Escherichia coli spheroplasts.
• Patch-clamp recordings to measure channel open probability (P_o).
• Development of an adenylate cyclase-knockout E. coli strain and generation of cysteine-free SthK constructs with mutations.

Main Results:

• SthK exhibits a higher P_o in cAMP than previously reported, with cGMP acting as a weak partial agonist.
• SthK expression toxicity in E. coli is attributed to cytoplasmic cAMP-mediated gating.
• A cysteine-free SthK mutant with increased P_o was successfully generated.

Conclusions:

• The developed SthK bacterial model provides a robust platform for investigating CNG channel gating.
• Understanding SthK gating contributes to elucidating the fundamental mechanisms of sensory signal transduction.
• This research overcomes previous limitations, paving the way for detailed structure-function analyses of CNG channels.