Cyclic di-AMP (c-di-AMP) is a second messenger which plays a major role in osmotic homeostasis in bacteria. In work by Quintana et al. (I. M. Quintana, J. Gibhardt, A. Turdiev, E. Hammer, et al., J Bacteriol 201:e00028-19, 2019, https://doi.org/10.1128/jb.00028-19), two Kup homologs from Lactococcus lactis were identified as high-affinity K+ importers whose activities are inhibited by direct binding of c-di-AMP. The results broaden the scope of K+ level regulation by c-di-AMP, with Kup homologs found in a number of pathogenic, commensal, and industrial bacteria.
Keywords: Lactococcus; cyclic di-AMP; osmotic stress; potassium uptake; second messenger.
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