Cytochrome c: A Multifunctional Protein Combining Conformational Rigidity with Flexibility

Abstract

Cytochrome has served as a model system for studying redox reactions, protein folding, and more recently peroxidase activity induced by partial unfolding on membranes. This review illuminates some important aspects of the research on this biomolecule. The first part summarizes the results of structural analyses of its active site. Owing to heme-protein interactions the heme group is subject to both in-plane and out-of-plane deformations. The unfolding of the protein as discussed in detail in the second part of this review can be induced by changes of pH and temperature and most prominently by the addition of denaturing agents. Both the kinetic and thermodynamic folding and unfolding involve intermediate states with regard to all unfolding conditions. If allowed to sit at alkaline pH (11.5) for a week, the protein does not return to its folding state when the solvent is switched back to neutral pH. It rather adopts a misfolded state that is prone to aggregation via domain swapping. On the surface of cardiolipin containing liposomes, the protein can adopt a variety of partially unfolded states. Apparently, ferricytochrome c can perform biological functions even if it is only partially folded.

Probing the non‐native states of Cytochrome c with resonance Raman spectroscopy: A tool for investigating the structure–function relationship

“…The research groups of Shelnutt and Schweitzer‐Stenner have extensively studied how heme–protein interactions affect the prosthetic heme group achieving important results that elucidate the heme–protein interactions and asymmetric deformations of the heme macrocycle. These results are not included in this review, and for a discussion of such studies, the reader is referred to their publications …”

“…In particular, direct interaction with cardiolipin (CL), a phospholipid of the inner mitochondrial membrane, induces acquisition of peroxidase activity and subsequent release of Cyt c into the cytosol, where it acts as an apoptosis initiator. Moreover, Cyt c has served as a model protein for investigating fundamental folding and unfolding processes induced by changes of pH, temperature as well as by the addition of denaturing agents …”

Electrocatalytic Properties of Immobilized Heme Proteins: Basic Principles and Applications

“…[1][2][3][4][5]33,34,38,39] A number of studies obtained the right orientation of ET proteins and redox enzymes using electrode (mainly Au) surfaces functionalized with self-assembled thiol monolayers or with spacers of variable lengths bearing endgroups of different nature. [1][2][3][29][30][31] Some proteins, moreover, such as nitrate reductase, [29,48] DMSO reductase [29] cytochrome c nitrite reductase, [49,50] sulfite oxidase, [51,52] cytochrome c [53,54] and cytochrome c 3 , [55] upon electron transfer process undergo more or less severe conformational changes (which, in turn, can modulate the following catalytic process). In a short time scale, typical of a CV measurement, the protein transfers electrons with the electrode without diffusing through the film.…”

The key role played by charge in the interaction of cytochrome c with cardiolipin

“…Conversely, the 414-nm dichroic band of the Ala mutants decreases in intensity, and in the Lys72Asn and Lys73Asn mutants this band is significantly weaker. As illustrated in the figure, the dichroic Soret band of ferric cyt c is characterized by a pronounced couplet, the two components resulting from the coupling of the heme group with different residues in the heme pocket [37,38]. In particular, the negative component (centered at 416 nm in the wt protein) is considered a probe of the native state, since it decreases, or disappears, as the protein rearranges into a less folded state [39,40].…”