Crystal engineering: a case study using the 24 kDa fragment of the DNA gyrase B subunit from Escherichia coli.

Site-directed mutagenesis was used to determine the efficacy of changing surface residues to improve crystal quality. Nine mutants of the 24 kDa fragment of the Escherichia coli DNA gyrase B subunit were produced, changing residues on the protein's surface. The mutations changed either the charge or the polarity of the wild-type amino acid. It was found that single amino-acid changes on the surface could have a dramatic effect on the crystallization properties of the protein and generally resulted in an improvement in the number of crystal-screen hits as well as an improvement in crystal quality. It is concluded that crystal engineering is a valuable tool for protein crystallography.