Coupling of MBP Fusion Protein Cleavage with Sparse Matrix Crystallization Screens to Overcome Problematic Protein Solubility

Crystal Clear Sparse matrices are a familiar tool to anyone who has set about seeking diffraction-quality crystals for X-ray crystallography studies. These multiwell plates provide an efficient way to screen multitudinous conditions for that just-right environment in which crystals can form. Jumping to a sparse matrix screen during one of the first steps of recombinant protein production might seem like muddled thinking, but Gruswitz et al. describe the method to the madness in a Benchmark beginning on p. 476. The authors first explain that maltose binding protein (MBP) is frequently used as a fusion tag to improve protein solubility, but since it usually must be removed before structural analysis, cleavage can often cruelly send the protein back to its original insoluble state. Gruswitz et al. therefore recommend performing the proteolytic removal of MBP in a sparse matrix setup, thus allowing for efficient screening of conditions in which the liberated polypeptide is soluble. Eight hours after preparing...