BPS2026 – The role of the C-terminal domain in NavSp1 channel modulation by temperature

Very little is known about the biological function and mechanisms of regulation for bacterial voltage-gated Na + channels (BacNa V s). The transmembrane domain fold is conserved between bacterial and eukaryotic voltage-gated Na + channels, but BacNa V channels have a C-terminal domain that is unique to the prokaryotic proteins and is composed of a membrane-proximal four-helix bundle and a distal tetrameric coiled coil. In the Na V Sp1 channel from the marine bacterium Ruegeria pomeriyi , the membrane-proximal C terminus has been proposed to function as a temperature sensor, conferring strong heat-sensitivity to channel activation. Here, we use electrophysiology and computational methods to describe a molecular mechanism through which the C terminus of Na V Sp1 channels regulates their sensitivity to heat and show how this mechanism could have a general role in sensing environmental factors in other species of bacteria. We establish that channel temperature-dependence is extremely sensitive to the amino acid sequence of the coiled coil at the distal C terminus. We find that the quaternary structure of the coiled coil exerts control on the state of the membrane-proximal C terminus, to either negatively or positively influence the temperature-and voltage-sensitivity of the channel. We demonstrate that key structural determinants associated with this mechanism can be predicted with surprising accuracy by AlphaFold, which we exploit to gain insight into the role of the C terminus in BacNa V channels in other species of bacteria. Learning how BacNa V channels are modulated in diverse bacteria can provide novel avenues to influence specific organisms associated with human disease, biogeochemical cycles, production of bioactive secondary metabolites, and biotechnological and agricultural processes.