Amino acid residues involved in reversible thiol formation and zinc ion binding in the Streptomyces reticuli redox regulator FurS

Abstract

Streptomyces reticuli produces a mycelium-associated enzyme, CpeB, whose N-terminal and C-terminal portions mediate heme-dependent catalase-peroxidase and heme-independent manganese-peroxidase activities, respectively. The regulator FurS governs transcription of the furS-cpeB operon. The thiol form of FurS contains one zinc ion per monomer and binds in this state to its cognate operator. Oxidation of SH groups within FurS induces the release of the zinc ion. Substitution of the codons for the amino acids cysteine 96, histidine 92 and 93, and tyrosine 59 in furs disrupts the in vivo repressor activity of FurS and results in enhanced synthesis of CpeB in corresponding S. lividans transformants. Biochemical and footprinting studies with FurS and its mutant derivatives revealed that the cysteine residues 96 and 99 are involved in reversible S-S bond formation, while cysteine 96 and the histidine residues 92 and 93 are required for zinc coordination, and tyrosine 59 is necessary for the binding of FurS to DNA. On the basis of these data, functional predictions can be made for the mycobacterial regulator FurA, a close homologue of FurS.