As shown in Figure 2, the interface is split into two sections �C one to display the motional Brusatol parameters and another to display the experimental and calculated data. Each section comprises a number of spreadsheets, allowing the user to easily modify input information. When the user changes the motional parameters in the parameter section, the program dynamically calculates the theoretical data and highlights regions in the calculated data that show significant deviation from the experimental data. This allows the user to interactively determine the effects of the motional parameters. NMRdyn can automatically optimize the microdynamic parameters for a set of experimental data in a routine relaxation analysis using an iterative protocol or study Oleuropein protein self-association using a grid-search approach. An iterative search can be started after the user has defined project-specific parameters and entered the experimental data in the data section. The optimized parameters and selected models from the analysis are displayed in the parameter section, while the calculated data are updated in the data section. To perform a grid-search, the user first specifies the desired range of values for the parameters involved in the grid search, and then the program searches for the optimal values while reporting a summary of the results for each point in the grid. The results for each grid point can be opened as a separate NMRdyn project so that the selected models and optimized parameters can be examined in more detail. Understanding the dynamics of a protein is often key to understanding its biological function. Some example applications of NMRdyn are reported in this section. One of the most informative motional parameters is S2, which describes the internal flexibility of a given amino acid in a protein. In Figure 3, we show the S2 values resulting from a relaxation analysis on a neuropeptide Y dataset, assuming isotropic tumbling and a monomeric species, and compare it to the output from relax, the most recent program for analyzing NMR relaxation data. The excellent agreement between NMRdyn and relax for both experimental and simulated relaxation data was used to validate NMRdyn��s implementation.