Direct observation of tiers in the energy landscape of a chromoprotein:: A single-molecule study

Single-molecule spectroscopic techniques were applied to individual pigments embedded in a chromoprotein. A sensitive tool to monitor structural fluctuations of the protein backbone in the local environment of the chromophore is provided by recording the changes of the spectral positions of the pigment absorptions as a function of time. The data provide information about the organization of the energy landscape of the protein in tiers that can be characterized by an average barrier height. Additionally, a correlation between the average barrier height within a distinct tier and the time scale of the structural fluctuations is observed.