Distinct extracytoplasmic siderophore binding proteins recognize ferrioxamines and ferricoelichelin in Streptomyces coelicolor A3(2)

Fluorescence and circular dichroism spectroscopy were used to study the binding affinity of the putative siderophore-binding proteins (SBPs) associated with the three gene clusters, DesE, CchF, and CdtB, recombinantly overproduced in Escherichia coli for cognate siderophores and noncognate siderophores. The remarkable specificity of the genes in the desferrioxamine (des) and coelichelin (cch) biosynthetic clusters which encode ATP-binding cassette (ABC) transporter components required for efficient uptake of ferrioxamine E and ferricoelichelin, respectively and other ferric-tris-hydroxamates shed light on the molecular basis for their substrate specificity.