Structural dynamics of proteins explored via time-resolved x-ray liquidography

The structure of a protein is closely related to its biological function. In this regard, structural changes, as well as static structures, have been scrutinized as essential elements in understanding and controlling the function of a protein. In particular, the structural change in the solution phase needs to be elucidated to properly understand protein functions under physiological conditions. Time-resolved x-ray liquidography (TRXL), also known as time-resolved x-ray solution scattering, has attracted attention as a powerful experimental method for studying the structural dynamics of proteins in the solution phase. Initially, TRXL was used to study the structural dynamics of small molecules in the solution phase, and later, its application was extended to probe the structural changes in proteins. Via TRXL, structural changes ranging from large quaternary movements to subtle rearrangements of the tertiary structures have been successfully elucidated. In this review, we introduce various studies using TRXL to investigate the structural dynamics of proteins. These include early TRXL studies on model systems, those on photoreceptor proteins, and recent studies using stimuli beyond the direct photoexcitation of proteins.