c-di-AMP recognition by Staphylococcus aureus PstA

• We solved the crystal structure of S. aureus PstA with and without c-di-AMP.
• PstA has a ferredoxin-like fold similar to PII-proteins.
• PstA has a different loop organization compared to canonical PII-proteins.
• PstA shows high affinity binding of c-di-AMP.
• c-di-AMP binding leads to loop reorganization in PstA.

Cyclic-di-AMP (c-di-AMP) is a bacterial secondary messenger involved in various processes, including sensing of DNA-integrity, cell wall metabolism and potassium transport. A number of c-di-AMP receptor proteins have recently been identified in Staphylococcus aureus. One of them - PstA - possesses a ferredoxin-like fold and is structurally related to the class of PII signal-transduction proteins. PII proteins are involved in a large number of pathways, most of them associated with nitrogen metabolism. In this study we describe the mode of c-di-AMP binding and subsequent structural changes of S. aureus PstA. An altered architecture in PstA compared to canonical PII proteins results in differences in ligand coordination.