RESEARCH ARTICLE Structural Dynamics of the Cereblon Ligand Binding Domain

Cereblon, a primary target of thalidomide and its derivatives, has been characterized struc-turally from both bacteria and animals. Especially well studied is the thalidomide binding do-main, CULT, which shows an invariable structure across different organisms and in complex with different ligands. Here, based on a series of crystal structures of a bacterial representative, we reveal the conformational flexibility and structural dynamics of this do-main. In particular, we follow the unfolding of large fractions of the domain upon release of thalidomide in the crystalline state. Our results imply that a third of the domain, including the thalidomide binding pocket, only folds upon ligand binding. We further characterize the structural effect of the C-terminal truncation resulting from the mental-retardation linked R419X nonsense mutation in vitro and offer a mechanistic hypothesis for its irresponsive-ness to thalidomide. At 1.2Å resolution, our data provide a view of thalidomide binding at atomic resolution