Terese Bergfors
Crystallization Platform, Dept. of Cell and Molecular Biology
Uppsala University

HT1: Crystallization

L1 (Lecture): Back to basics: How phase diagrams can help you


X-ray crystallography accounts for most of the structures in the Protein Data Bank.  But to crystallize a particular protein may require screening hundreds of conditions. Although crystals might appear in the initial screens, usually further optimization is needed. How does one recognize which results from these kits are worth optimizing?

Understanding the phase diagram can help answer that question.  Phase diagrams are maps of the events (phase transitions) that occur in the crystallization setups.  The first part of this talk will give an overview of the steps in a crystallographic project and then look at:

  • two critical events in the phase diagram: supersaturation and nucleation
  • how precipitants drive the protein into a state of supersaturation

In the second part, the lecture will look at the following questions, from the perspective of an academic laboratory. Examples of what worked and what did not will be presented for our protein targets from Mycobacterium tuberculosis.

  • What is the single most important parameter in screening?
  • How many conditions should the initial screen contain: 15, 150 or 15,000?
  • Are all crystallization kits equally successful?
  • Which is more critical: the choice of precipitant or the kinetic pathway?

Suggested readings:

  •  Bergfors, T. (editor) Protein Crystallization, Third Edition 2022. International University Line, La Jolla, 670 pages.
  • McPherson, A. and Gavira, JA. Introduction to protein crystallization. 2014. Acta Cryst F, vol. 70, 2-20.
  • Asherie, N. Protein crystallization and phase diagrams. 2004. Methods vol. 34, 266-272.