| dc.description.abstract | K^+ channels are widely conserved among all species. Although bacterial K^+ channels are often used in structural and biophysical assays as models for their eukaryotic homologs, little is known about their physiological role in bacteria. In vivo characterization of bacterial channels has been difficult because an obvious phenotype is not always associated with a null mutant. The E. coli genome contains one K^+ -selective channel, Kch, which remains poorly understood despite attempts at characterization. In order to elucidate the physiological function of Kch, we performed a large-scale computational protein co-evolution analysis to predict protein interaction partners of Kch. We hypothesized that determining which proteins the K^+ channel was predicted to interact with could reveal insight into its function. Linking the channel to proteins with known biological functions would allow for targeted experimental validation of the predicted interactions and further in vivo characterization. Our analysis revealed that Kch was predicted to co-evolve with proteins involved in oxidation-reduction processes, cell division, and metabolism.
We first asked if loss of the channel resulted in a growth defect in various media. In rich media, the Δkch strain exhibited a slight growth defect upon entering mid-exponential phase, which could be rescued by the addition of a fermentable, but not an oxidizable, carbon source. Replacement of the Δkch mutation with a functional kch gene failed to rescue the growth defect, and whole genome sequencing revealed additional mutations in the background, including a point mutation in ubiH (ubiHV223G ). UbiH is required for biosynthesis of the electron carrier molecule, ubiquinone, which functions in the aerobic electron transport chain (ETC). Characterization revealed that the ubiH^V223G mutation acts to reduce the overall efficiency of the aerobic ETC, leading us to hypothesize that Kch was involved in modulation of the membrane potential (ΔΨ). CRISPR interference (CRISPRi)-mediated kch depletion results in growth defects and ΔΨ fluctuations, indicating that the native function of Kch is rapid modulation of ΔΨ. Using a variety of novel approaches, we demonstrate that Kch is important for adaptation to conditions that promote rapid growth, expanding our limited understanding of the physiological functions of microbial K^+ channels. | en |
