Bioactive apo-ferredoxin–polycation–clay composites for iron binding

Abstract

Trace concentrations of heavy metals cause health and environmental hazards. Specifically, trace concentrations of iron induce biofilm formation which is of great concern in water systems. To remove the iron, protein–polycation–clay composites were designed based on the hypothesis that the adsorbed apo-ferredoxin (apo-mFd: mFd protein without the 2Fe–2S cluster) chelates iron. Fe²⁺ chelation by apo-mFd protein was established by optical spectroscopy and gel electrophoresis. To reduce its biodegradation, apo-mFd was adsorbed to montmorillonite and these composites were characterized by X-ray diffraction, zeta potential and adsorption isotherms. The apo-mFd–montmorillonite did not chelate iron with high efficiency; however, when a polycation–apo-mFd complex was adsorbed to the clay, the protein retained its chelating characteristics and specific interactions of iron with the biocomposite were established. Results present the innovative tailoring of bioactive protein–polycation–clay composites which may be applicable in many fields, e.g., protein immobilization, drug delivery and water treatment.