Conjugation of cytochrome c with ferrocene-terminated hyperbranched polymer and its influence on protein structure, conformation and function

Interaction mechanism of a new hyperbranched polyurethane-based ferrocene (HPU-Fc) with cytochrome c (cyt c) and cyt c structure and conformation change induced by HPU-Fc were investigated using cyclic voltammogram(CV), differential pulse voltammetry (DPV), circular dichroism (CD), fluorescence, synchronous fluorescence and absorbance spectroscopy technique. The peroxidase activity of cyt c in the presence of HPU-Fc was also studied. The structure and conformation of protein are relatively stable at moderate concentration of HPU-Fc without obvious perturbation of the heme pocket and significant changes in protein secondary structure. Conjugation of cyt c with excessive HPU-Fc (over about 3 times of cyt c) slightly changed the a-helix structure in protein, disturbed the microenvironment around heme as well as away from the heme crevice, which caused the changes of the electrochemical behavior and the absorption spectra. Reasonable amount of HPU-Fc has no significant influence on the protein enzymatic activity, while excess HPU-Fc may cause a conformation not suitable for H2O2 activation and guaiacol oxidation. The interaction of HPU-Fc with cyt c and the conservation of protein function at suitable HPU-Fc amount make prepared complex promising for the synergistic anticancer therapy. (C) 2016 Elsevier B.V. All rights reserved.