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 su rface residues to improve crystal quality. Nine mutants of the 24 kDa fragm ent of the Escherichia coli DNA gyrase B subunit were produced, changing re sidues 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-a cid changes on the surface could have a dramatic effect on the crystallizat ion properties of the protein and generally resulted in an improvement in t he number of crystal-screen hits as well as an improvement in crystal quali ty. It is concluded that crystal engineering is a valuable tool for protein crystallography.