Members of this family are all transcribed from the spoVA operon [1]. Bacillus and Clostridium are two well studied endospore forming bacteria. Spore formation provides a resistance mechanism in response to extreme or unfavourable environmental conditions such as heat, radiation, and chemical agents or nutrient deprivation. The reverse process termed germination takes place where spores develop into growing cells in response to nutrient availability or stress reduction. Nutrient germinant receptors (GRs) and the SpoVA proteins are important players in the germination process. In B.subtilis the SpoVAC and SpoVAEB, belonging to this domain family, are predicted to be membrane proteins, with two to five membrane spanning. Biophysical and biochemical studies suggest that SpoVAC acts as a mechano-sensitive channel with properties that would allow the release of Ca-DPA (dipicolinic acid) and amino acids during germination of the spore. The release of Ca-DPA is a crucial event during spore germination. When expressed in E.coli SpoVAC provides protection against osmotic downshift. Furthermore, SpoVAC acts as channel that facilitates the efflux down the concentration gradient of osmolytes up to a mass of at least 600 Da [2]. Another conserved SpoVA protein in all spore-forming bacteria is SpoVAEb, which appears to be an integral membrane protein with no known function [3].

1: The products of the spoVA operon are involved in dipicolinic acid uptake into developing spores of Bacillus subtilis. Tovar-Rojo F, Chander M, Setlow B, Setlow P; J Bacteriol 2002;184:584-587. PMID:11751839

2: Bacillus subtilis spore protein SpoVAC functions as a mechanosensitive channel. Velasquez J, Schuurman-Wolters G, Birkner JP, Abee T, Poolman B; Mol Microbiol. 2014;92:813-823. PMID:24666282

3: Characterization of Clostridium difficile Spores Lacking Either SpoVAC or Dipicolinic Acid Synthetase. Donnelly ML, Fimlaid KA, Shen A; J Bacteriol. 2016;198:1694-1707. PMID:27044622