Redox thermodynamics of cytochromes c subjected to urea induced unfolding

How to Turn an Electron Transfer Protein into a Redox Enzyme for Biosensing

Cytochrome c is a small globular protein whose main physiological role is to shuttle electrons within the mitochondrial electron transport chain. This protein has been widely investigated, especially as a paradigmatic system for understanding the fundamental aspects of biological electron transfer and protein folding. Nevertheless, cytochrome c can also be endowed with a non-native catalytic activity and be immobilized on an electrode surface for the development of third generation biosensors. Here, an overview is offered of the most significant examples of such a functional transformation, carried out by either point mutation(s) or controlled unfolding. The latter can be induced chemically or upon protein immobilization on hydrophobic self-assembled monolayers. We critically discuss the potential held by these systems as core constituents of amperometric biosensors, along with the issues that need to be addressed to optimize their applicability and response.

Adsorbing surface strongly influences the pseudoperoxidase and nitrite reductase activity of electrode-bound yeast cytochrome c. The effect of hydrophobic immobilization

The Met80Ala and Met80Ala/Tyr67Ala variants of S. cerevisiae iso-1 cytochrome c (ycc) and their adducts with cardiolipin immobilized onto a gold electrode coated with a hydrophobic self-assembled monolayer (SAM) of decane-1-thiol were studied through cyclic voltammetry and surface-enhanced resonance Raman spectroscopy (SERRS). The electroactive species - containing a six-coordinate His/His axially ligated heme and a five-coordinate His/- heme stable in the oxidized and reduced state, respectively - and the pseudoperoxidase activity match those found previously for the wt species and are only slightly affected by CL binding. Most importantly, the reduced His/- ligated form of these variants is able to catalytically reduce the nitrite ion, while electrode-immobilized wt ycc and other His/Met heme ligated variants under a variety of conditions are not. Besides the pseudoperoxidase and nitrite reductase functions, which are the most physiologically relevant abilities of these constructs, also axial heme ligation and the equilibria between conformers are strongly affected by the nature - hydrophobic vs. electrostatic - of the non-covalent interactions determining protein immobilization. Also affected are the catalytic activity changes induced by a given mutation as well as those due to partial unfolding due to CL binding. It follows that under the same solution conditions the structural and functional properties of immobilized ycc are surface-specific and therefore cannot be transferred from an immobilized system to another involving different interfacial protein-SAM interactions.

Met80 and Tyr67 affect the chemical unfolding of yeast cytochromec: comparing the solutionvs.immobilized state

The motional regime affects the unfolding propensity and axial heme coordination of the Met80Ala and Met80Ala/Tyr67Ala variants of yeast iso-1 cytochromec.