Differential dynamical effects of macromolecular crowding on an intrinsically disordered protein and a globular protein: Implications for in-cell NMR spectroscopy

In-cell NMR provides a valuable means to assess how macromolecules, with concentrations up to 300 g/L in the cytoplasm, affect the structure and dynamics of proteins at atomic resolution. Here an intrinsically disordered protein, a-synuclein (alpha SN), and a globular protein, chymotrypsin inhibitor 2 (Cl2) were examined by using in-cell NMR. High-resolution in-cell spectra of aSN can be obtained, but Cl2 leaks from the cell and the remaining intracellular Cl2 is not detectable. Even after stabilizing the cells from leakage by using alginate encapsulation, no Cl2 signal is detected. From in vitro studies we conclude that this difference in detectability is the result of the differential dynamical response of disordered and ordered proteins to the changes of motion caused by the increased viscosity in cells.