Exploiting Protein Engineering and Crystal Polymorphism for Successful X-ray Structure Determination

The preparation of high quality crystals is a central issue in the process of determining 3D structures of biomolecules by X-ray crystallography. The success of this key step frequently depends upon the right choice and the rigorous characterization of the target. Further, the identification and refinement of the growth conditions of a supplementary crystalline polymorph may be profitable. Four representative examples illustrate how the critical parameters can be handled. These case studies include chemically and structurally different biological entities: bacterial RNA chaperone Hfq, human mitochondrial enzyme tyrosyl-tRNA synthetase, yeast exosome subcomplex, and icosahedral virus causing grapevine fanleaf disease. The winding paths which led to the determination of each structure at atomic resolution are described together with related crystallogenesis strategies.