FTIR and 2D-FTIR spectroscopic study of cytochrome c 552 adsorbed on anionic and hydrophobic surfaces

In the respiratory chain of prokaryotic and eukaryotic organisms, cytochrome c (Cyt-c) acts as an electron carrier between complexes III (cytochrome c reductase) and IV (cytochrome c oxidase). Binding to its reaction partners is governed by electrostatic interactions involving the positively lysine-rich domain on the front surface of Cyt-c [1]. Such a domain was regarded as a common structural template for soluble type-c cytochromes until it was shown recently that cytochrome c 552 (Cyt-c 552), which serves as an electron transporter in the respiratory chain of Thermus thermophilus, does not exhibit a cluster of lysine residues on the protein surface [2]. Thus, it may be that the molecular interactions of Cyt-cn552 with its natural redox partners are qualitatively different compared to Cyt-c and may even involve hydrophobic interactions. This work is dedicated to contribute to a better understanding of these intermolecular interactions and their potential relevance for the electron transfer process. In order to study the effect of electrostatic and hydrophobic interactions on the structure of Cyt-cin552, montmorillonite and talc clays were chosen as model systems to mimic anionic and uncharged protein domains, respectively. We have employed FTIR and 2D-FTIR spectroscopy that can provide information about the secondary structure and the protein dynamics [3, 4].