CcaR is an autoregulatory protein that binds to the ccaR and cefD-cmcI promoters of the cephamycin C-clavulanic acid cluster in Streptomyces clavuligerus

The putative regulatory CcaR protein, which is encoded in the beta-lactam supercluster of Streptomyces clavuligerus, has been partially purified by ammonium sulfate precipitation and heparin affinity chromatography. In addition, it was expressed in Escherichia coli, purified as a His-tagged recombinant protein (rCcaR), and used to raise anti-rCcaR antibodies. The partially purified CcaR protein from S. clavuligerus was able to bind DNA fragments containing the promoter regions of the ccaR gene itself and the bidirectional cefD-cmcI promoter region. In contrast, CcaR did not bind to DNA fragments with the promoter regions of other genes of the cephamycin-clavulanic acid supercluster including lat, blp, claR, car-cyp, and the unlinked argR gene. The DNA shifts obtained with CcaR were prevented by anti-rCcaR immunoglobulin G (IgG) antibodies but not by anti-rabbit IgG antibodies. ccaR and the bidirectional cefD-cmcI promoter region were fused to the xylE reporter gene and expressed in Streptomyces lividans and S. clavuligerus. These constructs produced low catechol dioxygenase activity in the absence of CcaR; activity was increased 1.7- to 4.6-fold in cultures expressing CcaR. Amplification of the ccaR promoter region lacking its coding sequence in a high-copy-number plasmid in S. clavuligerus ATCC 27064 resulted in a reduced production of cephamycin C and clavulanic acid, by 12 to 20% and 40 to 60%, respectively, due to titration of the CcaR regulator. These findings confirm that CcaR is a positively acting autoregulatory protein able to bind to its own promoter as well as to the cef-cmcI bidirectional promoter region.