Copper Storage Protein From Streptomyces Lividans

The ability of copper to cycle between two redox states (CuI/CuII), each having a preference for either soft or hard ligands, gives rise to a diverse spectrum of coordination spheres within protein scaffolds that results in a broad range of functionalities. Maintaining cellular copper bioavailability and preventing the detrimental effects associated with excess CuI is critical for cell viability. In the bacterial cytosol, regulatory systems exist that are chemically tuned to constrain and regulate cuprous ion bioavailability through high-affinity-binding sites that use predominately cuprous-thiolate coordination chemistry. Recently, a family of four-helix bundle proteins with a cysteine-rich core has been discovered to reside in the bacterial cytosol. These proteins have been named copper storage proteins (Csps), reflecting their ability to coordinate up to 20 cuprous ions in the cysteine-rich core. In the Gram-positive, filamentous bacterium, Streptomyces lividans, a Csp is present. The copper regulatory systems in S. lividans have been well studied and the extracytoplasmic copper-trafficking pathways, essential to initiate the copper-dependent morphological differentiation, identified. The role the Csp plays in the copper biochemistry of S. lividans has been investigated from both a biological and bioinorganic chemistry perspective, and the current understanding is summarized.