Determination of the three-dimensional structure of toxins by protein crystallography

Protein crystallography has significantly contributed to the development of many areas of biochemical research, particularly in the understanding of phenomena related to molecular recognition. Examples include the formation of enzyme-substrate complexes (and their subsequent catalysis), host cell invasion by viruses, antigen neutralization and peptide display by proteins of the immune system and many others. More recently, protein crystallography has also proved to be of great value in unraveling the molecular basis of many diseases as well as in the development of new drugs for their treatment. The X-ray diffraction technique in the elucidation of macromolecular structures is situated at the interface between the traditional research fields of biology, biochemistry, chemistry and physics where researchers are united by a common interest in the detailed understanding of macromolecule function and its relationship to three-dimensional structure. The purpose of this review is to describe, without resort to mathematical detail, all of the necessary steps for the complete determination of a three-dimensional structure by X-ray diffraction techniques. The basic procedures used for protein isolation and crystallization, crystallographic data collection and analysis and, finally, structure determination and refinement are all briefly reviewed. As such our efforts are not directed towards the specialist. Rather, it is our hope that the information presented will aid interested readers from other fields in the understanding of more specialized literature and who may wish to employ the information contained therein in the planning of their biological research. We hope that in so doing we will make clear both the power and limitations of the technique.