 Abstract cyclic DIAMP, CDIAMP, is an important second messenger in bacterial cells which regulates many proteins necessary for cellular functions. It has been shown to control the activity of potassium and osmolite transporters, including the Chimae protein from bacillus subtilis, which is responsible for potassium ion uptake. When Chimae is exposed to high levels of potassium, its activity is reduced due to the binding of CDIAMP. This causes the protein to adopt an inward occluded confirmation, preventing further potassium uptake. The structure of Chimae with CDIAMP bound was determined using cryo, electron microscopy and molecular dynamic simulations, providing insight into how CDIAMP affects the protein's function. This article was authored by Michael F. Fuss, Jan-Philipp Wieferig, Robin A. Koi, and others.