Structural and kinetic studies of a copper sensor protein in Streptomyces lividans

The production of antibiotics, antifungal, enzymes and anti-tumoral agents of economical importance in Streptomyces lividans occurs during the copperdependant morphological switch step of its distinct lifecyle. However, copper can be toxic to the cell if it is not well regulated, affecting copper homeostasis. The regulation of the concentrations of copper is performed by CsoR, a Cu(I)-metalloregulator of the CsoR/RcnR family, on upon Cu(I) binding, it dissociates from its own csoR regulon. This event leads to Cu(I) to be trafficked outside the cytosol via a CopZ chaperoning system. Although Cu(I)-bound structures of CsoR/RcnR family members have been solved, its still unclear how CsoR dissociates from DNA upon Cu(I) binding and how promiscuous its metal ion binding site is, i.e., if it other metals bind and trigger a similar allosteric response as Cu(I) does. Through a structural and kinetic approach, these questions were explored on this work, in order to give insights at atomic and mechanistic level in this metalloregulator family. A novel CsoR structure at pH 6 revealed a striking quasi-Cu(I) bound state, which provides important information on how CsoR may bind to DNA. A mechanism of metal binding to Cu(I) and a non-cognate metal, Ni(II) is proposed, with novel insights on metal selectivity and specificity in this poorly understood family of bacterial metalloregulators.