PNNL

Abstract

Confined and hindered protein motions are generally found in living cells, with tethered rotational motions of proteins or protein domains particularly associated with and relevant to the early events of molecular interactions in cell signaling at extra- and intracellular membrane surfaces. Ensemble-averaged time-resolved fluorescence anisotropy has been extensively applied to study the protein rotational and conformational motion dynamics under physiologically relevant conditions. However, the spatial and temporal inhomogeneities of the non-synchronizable stochastic protein rotational and conformational motions are extremely difficult for such ensemble-averaged measurements to characterize. Here, we report on a demonstration of the single-molecule nanosecond anisotropy and its application to studying the tethered protein motion of a T4 lysozyme on a biologically comparable surface under water. The rotational motions of the tethered proteins are confined in a half-sphere volume primarily defined by the linker and the surface. We have observed dynamic inhomogeneity of the rotational diffusion dynamics, i.e., diffusion rate fluctuation, due to interactions between the proteins and the surface. However, we also found that the long-time averages of the dynamically inhomogeneous diffusion rates of single molecules are essentially homogeneous amongst the single molecules examined.