Diffractive optics based nonlinear optical studies of protein motions: From inertial collective modes to "protein quakes"

Recent advances in nonlinear spectroscopy are discussed as a means to probe in real time the highly correlated structural changes involved in function ally significant protein motions - over nine decades in dynamic range. The dynamics and energetics of these processes can be followed with unprecedent ed sensitivity by using diffractive optics to generate the proper beam geom etries, along with a reference for true phase sensitive detection of the si gnal field. Conventional descriptions in terms of glass dynamics are found not to hold over the complete dynamic relaxation pathway. A paradigm based on the coupling of reaction coordinates to collective modes is invoked to e xplain the biomechanics and energy transduction processes involved in deter ministic protein motions.