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Structural Changes of Cytochrome c 552 from Thermus thermophilus Adsorbed on Anionic and Hydrophobic Surfaces Probed by FTIR and 2D‐FTIR Spectroscopy
Author(s) -
Lecomte Sophie,
Hilleriteau Christophe,
Forgerit Jean Pierre,
Revault Madeleine,
Baron MarieHélène,
Hildebrandt Peter,
Soulimane Tewfik
Publication year - 2001
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/1439-7633(20010302)2:3<180::aid-cbic180>3.0.co;2-b
Subject(s) - fourier transform infrared spectroscopy , adsorption , chemistry , spectroscopy , infrared spectroscopy , chemical engineering , organic chemistry , engineering , physics , quantum mechanics
The structural changes of cytochrome c 552 bound to anionic and hydrophobic clay surfaces have been investigated by Fourier transform infrared spectroscopy. Binding to the anionic surface of montmorillonite is controlled by electrostatic interactions since addition of electrolyte (0.5 mol L −1 KCl) causes desorption of more than ⅔ of the protein molecules. Electrostatic binding occurs through the back side of the protein (i.e., remote from the heme site) and is associated only with subtle changes of the secondary structure. In contrast, adsorption to the hydrophobic surface of talc leads to a decrease in α‐helical structure by ca. 5 % and an increase in β‐sheet structure by ca. 6 %. These structural changes are attributed to a hydrophobic region on the front surface of cytochrome c 552 close to the partially exposed heme edge. This part on the protein surface is identified as the interaction domain for talc and most likely also serves for binding to the natural reaction partner, a ba 3 ‐oxidase. Fourier transform infrared spectra of cytochrome c 552 and the clay–cytochrome c 552 complexes have been measured as a function of time following dissolution and suspension in deuterated buffer, respectively. A two‐dimensional correlation analysis was applied to these spectra to investigate the dynamics of the structural changes in the protein. For both complexes, adsorption and subsequent unfolding processes in the binding domains are faster than the time resolution of the spectroscopic experiments. Thus, the processes that could be monitored are refolding of peptide segments and side chain rearrangements following the adsorption‐induced perturbation of the protein structure and the solvation of the adsorbed protein. In each case, side chain alterations of solvent‐exposed tyrosine, aspartate, and glutamate residues were observed. For the cytochrome c 552 –talc complex, these changes are followed by a slow refolding of the peptide chain in the binding domain and, subsequently, a further H/D exchange of amide group protons.