L2: Macromolecular crystallization techniques
University of Jordan
Traditionally, protein crystallization has been essentially empirical. The purified protein is usually mixed with various crystallization agents that were selected in a trial-and-error fashion. However, the crystallization properties of proteins vary greatly: some crystallize readily, whereas others have proven extremely difficult or even impossible to obtain in a crystalline state. The most frustrating scenario in protein crystallization experiments is when large, gorgeous crystals do not diffract. Other common scenarios include a shower of tiny crystals, low-quality crystals, phase separation, amorphous precipitate, and the most common scenario, no crystals at all. Many parameters can be adjusted in these experiments, such as temperature, pH, ionic strength, precipitant concentration, and protein concentration. Additives that can alter the structural state of protein, such as metal ions, inhibitors, cofactors, or other conventional small molecules, can also impact crystallization. The protein construct itself is a critical variable that can be ignored.
Luckily, many approaches have been employed successfully by combining the spectrum of factors that influence and promote crystallization. A brief overview of these tools and tricks will be covered in this lecture.