Marcus Group Research

The Marcus group studies the structure and dynamics of macromolecules in biological environments.  These include the diffusive motions and internal structural changes of proteins in membranes and in living cells, as well as the conformational fluctuations of macromolecular machines that interact with and manipulate DNA.

To elucidate the conformations of macromolecular complexes, and to monitor their time dependent behavior, we develop and apply linear and nonlinear spectroscopic methods that are sensitive to the electronic couplings between fluorescent chromophore labels.  Spectroscopic characterization of exciton-coupled dimer probes, which are attached at specific locations on the macromolecules, allows us to observe functionally important macromolecular conformations.  Extension of our techniques to single molecule fluorescence imaging allows us to observe bio-molecular events in real time.

We developed phase-modulation two-dimensional fluorescence spectroscopy (PM-2D FS) to characterize the exciton-coupling of dimer probes, and to determine dimer conformation.  These experiments yield two-dimensional optical spectra, which in analogy to two-dimensional nuclear magnetic resonance (2D NMR), provide information about the distribution of states, and the coupling between states.  We have also developed low-signal detection methods such as Fourier imaging correlation spectroscopy (FICS), to monitor the translational motions and conformational fluctuations of labeled macromolecules in solution.