The response to copper stress in Streptomyces lividans extends beyond genes under the direct control of a Copper sensitive operon Repressor protein (CsoR)

A Copper sensitive operon Repressor protein has been identified in Streptomyces livdians (CsoRSl) and found to regulate copper homeostasis with attomolar affinity for Cu(I). Solution studies reveal apo- and CuI-CsoRSl to be a tetramer assembly and a 1.7 Å resolution crystal structure of apo-CsoRSl reveals that a significant conformational change is necessary to enable Cu(I) binding. In silico prediction of the CsoR regulon was confirmed in vitro (EMSA) and in vivo (RNA-seq) which highlighted that next to the csoR gene itself, the regulon consists of two Cu(I) efflux systems involving a CopZ-like copper metallochaperone protein and a CopA P1-type ATPase. While deletion of csoR has only minor effects on S. lividans development when grown under high copper concentrations, mutations of the Cu(I) ligands decrease tolerance to copper as a result of the Cu(I)-CsoR mutants failing to disengage from the DNA targets, thus inhibiting the derepression of the regulon. RNA-seq experiments carried out on samples incubated with exogenous copper and a ΔcsoR strain showed that the set of genes responding to copper stress is much wider than anticipated and largely extends beyond genes targeted by CsoR. This suggests more control levels are operating and directing other regulons in copper homeostasis beside the CsoR regulon