B acillus subtilis spore protein SpoVAC functions as a mechanosensitive channel

Summary A critical event during spore germination is the release of Ca ‐ DPA (calcium in complex with dipicolinic acid). The mechanism of release of Ca ‐ DPA through the inner membrane of the spore is not clear, but proteins encoded by the B acillus subtilis   spoVA operon are involved in the process. We cloned and expressed the spoVAC gene in E scherichia coli and characterized the SpoVAC protein. We show that SpoVAC protects E . coli against osmotic downshift, suggesting that it might act as a mechanosensitive channel. Purified SpoVAC was reconstituted in unilamellar lipid vesicles to determine the gating mechanism and pore properties of the protein. By means of a fluorescence‐dequenching assay, we show that SpoVAC is activated upon insertion into the membrane of the amphiphiles lyso PC and dodecylamine. Patch clamp experiments on E . coli giant spheroplast as well as giant unilamellar vesicles ( GUVs ) containing SpoVAC show that the protein forms transient pores with main conductance values of about 0.15 and 0.1 nS respectively. Overall, our data indicate that SpoVAC acts as a mechanosensitive channel and has properties that would allow the release of Ca ‐ DPA and amino acids during germination of the spore.