Exploring the Response of Bacterial Cyclic Nucleotide Gated (bCNG) Ion Channels to Mechanical Stress

Abstract

The bacterial cyclic nucleotide gated (bCNG) ion channel family contains a N-terminal channel domain, which is homologous to the Mechanosensitive Channel of Small Conductance (MscS) and a ligand binding domain with sequence similarity to known cyclic nucleotide binding domains. Previously, we have demonstrated that some of these channels gate in response to cyclic adenosine monophosphate alone [Caldwell, et al, BBA 2010, 1798, 1750-1756]. Here we explore the ability of bCNG channels to gate in response to mechanical stress, which one might predict based on their significant sequence homology to MscS. To this end, we measured the ability of fourteen distinct bCNG channels from several different bacterial strains to rescue E. coli lacking mechanosensitive channels (MscS/MscL/MscK null) from osmotic downshock. In our studies, only two bCNG channels exhibit limited ability to rescue bacteria from osmotic downshock. These two channels were found in bacterial strains with genomes encoding for multiple variants of the bCNG gene. Only one bCNG channel variant in each strain was capable of rescuing E.coli from osmotic downshock, implying that each gene product may have a unique role or that the two gene products may work in concert. Additionally, truncation of the cyclic nucleotide binding domain in some non-mechanosensitive variants of bCNG increases their response to mechanical stress.