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Proteins are supramolecular machines that carry out a wide range of different functions, many of which require flexibility. Up until now spontaneous conformational fluctuations of proteins have always been assumed to reflect a stochastic random process. However, if changing between different conformational states was random, then it would be difficult to understand how conformational control of protein function could have evolved. Here we demonstrate that a single protein can show conformational memory. This is exactly the process that can facilitate the evolution of control of switching between two conformational states that can then be used to regulate protein function.

The light harvesting complex LH2 is a chromoprotein that is an ideal system for studying protein dynamics via the spectral fluctuations of the emission of its intrinsic chromophores. We have immobilized these complexes in a polymer film and studied the fluctuations of the fluorescence intensity from individual complexes over 9 orders of magnitude in time. Combining time-tagged detection of single photons with a change-point analysis has allowed the unambigeous identification of the various intensity levels due to the huge statistical basis of the data set. We propose that the observed intensity level fluctuations reflect conformational changes of the protein backbone that might be a precursor of the mechanism from which nonphotochemical quenching of higher plants has evolved.

In our experimental study on the linear stability of gravity-driven films flowing over inclined topographies, we consider a fundamental question: does the topography's specific shape matter in general for the stability of film flows? In order to understand this complex problem, we used five topographies of different shapes. For each topography, we characterized the basic flow by measuring the flow field and the free surface contour. Experiments on the flow's linear stability followed. We obtained astonishing results on how the topography's shape can manipulate both the basic flow and the linear stability of gravity-driven films. C 2015 AIP Publishing LLC.