The amino-terminal structure of human fragile X mental retardation protein obtained using precipitant-immobilized imprinted polymers

Flexibility is an intrinsic property of proteins and essential for their biological functions. However, because of structural flexibility, obtaining high-quality crystals of proteins with heterogeneous conformations remain challenging. Here, we show a novel approach to immobilize traditional precipitants onto molecularly imprinted polymers (MIPs) to facilitate protein crystallization, especially for flexible proteins. By applying this method, high-quality crystals of the flexible N-terminus of human fragile X mental retardation protein are obtained, whose absence causes the most common inherited mental retardation. A novel KH domain and an intermolecular disulfide bond are discovered, and several types of dimers are found in solution, thus providing insights into the function of this protein. Furthermore, the precipitant-immobilized MIPs (piMIPs) successfully facilitate flexible protein crystal formation for five model proteins with increased diffraction resolution. This highlights the potential of piMIPs for the crystallization of flexible proteins. Obtaining a protein crystal structure can be hampered by molecular flexibility. Here, the authors use precipitant-immobilized molecularly imprinted polymers to produce high quality crystals, such as of the fragile X mental retardation protein N-terminal domain, allowing for a detailed structural and functional analysis.