Abstract
Copper is essential for life but toxic, therefore all organisms control tightly its intracellular abundance. Bacteria have indeed whole operons devoted to copper resistance, including efflux pumps, oxidases, etc. Recently, the CopM protein of the CopMRS operon was described as an important element for copper tolerance in Synechocystis. The protein consists of a domain of unknown function, and was suggested to act as a periplasmic/extracellular copper binder. This work describes a bioinformatic characterization of CopM including significant structural models based on homology and coevolution, to help expand on the recently reported experiments. The protein is predicted to be membrane-anchored, not secreted. Two disordered regions are predicted, both possibly involved in protein-protein interactions. The models disclose a 4-helix bundle fold with several potential copper-binding sites, some involving residues from the disordered regions. Metal-binding sites are predicted to be largely buried, suggesting that copper binding could induce structuring and possibly alter interactions with other proteins.