Structure of cytochrome c at the interface with magnetic CoFe₂O₄nanoparticles

Yeast and horse cytochrome c are attached to 6 nm CoFe2O4 nanoparticles and their structure is studied as a function of the nanoparticle surface chemistry. For yeast cytochrome c, the attachment is covalent and site-specific via dithiol cross-linkage between cysteine 102 and dimercaptosuccinic acid, the nanoparticle ligand. To control site-specificity and allow better characterization of non-specific interactions, horse cytochrome c is non-specifically linked to the nanoparticle. Circular dichroism shows that the structure of both proteins is affected by linkage to the CoFe2O4 nanoparticle. Non-specific adsorption depends strongly on the surface properties of the nanoparticles. Co-functionalization with lysine improves protein folding, most likely by decreasing the nanoparticle net charge and impeding carboxylic acids residues from binding to surface cobalt and iron atoms. Higher protein coverage also helps folding for both yeast and horse cytochrome c.