In this reporting period, papers dealing with the following topics appeared in print: (1)The domain motions of calmodulin probed by NMR relaxation at multiple fields (2)The analysis of nonequilibrium single molecule pulling experiments to yield kinetic information (3) The analysis of single macromolecule fluorescence resonance energy transfer experiments to yield free-energy profiles of protein folding (4)The statistics of transitions in single molecule kinetics. The first paper deals with the problem of analyzing NMR relaxation data to yield information about the amplitude and time scale of interdomain motions in proteins and is a collaboration with the experimental group of Nico Tjandra. This area has been one of our long term interests. The remaining three papers deal with our main new interest, namely the analysis of single molecule experiments. The first of these,done in collaboration with my colleague Gerhard Hummer, intoduces a new approach to extract kinetic information from experiments in which mechanical forces exerted by laser tweezers or atomic force microscopes are used to drive rare transitions in single molecules such as unfolding of a protein or dissociation of a ligand. Our procedure is based on the rigorous analysis of a simple microscopic model and has been tested against the result of computer simulation. It is much better than the conventional approach and is expected to replace it. The last two papers deal with the theory required to interpret Forster resonance energy transfer experiments on protein folding. In these experiments the number of photons emitted by a donor and an acceptor are monitoried. These contain structural information because the efficiency of energy transfer between tne donor and acceptor depend on the distance between them. Given an arbitrary dynamical scheme we showed how to calculate the probability distribution of the energy transfer obtained for fixed time windows. We specifically considered the distributions for a random coil protein and for two state folding-unfolding kinetics and determined how the free energy profiles extracted from such distributions depend on the size of the time window. This kind of analysis is essential for the meanigful interpretation of experiments.
Showing the most recent 10 out of 20 publications
