Cryocooling

Because macromolecular crystals are sensitive to X-rays, so they are usually cryogenically cooled to ~100K prior to X-ray exposure. This slows the X-ray damage processes.

BUT, the cooling process itself can damage the crystal. We are trying to understand this cooling damage with the aim of improving cooling techniques. We are interested in the following related questions:

1. What is the nature of cooling damage to crystals?
2. How do cryoprotectants work to limit cooling damage?
3. Can cooling damage be reversed in a predictable way based on the nature of the damage?
4. How much information about a particular macromolecular crystal is required to choose a good cryoprotectant?

Our work and others' have suggested the following mechanism for cryoprotectant action. It appears that cryoprotectants work in part by adjusting the thermal contraction of the bulk solvent to match the contraction of the interstitial spaces. Our papers on this topic:

1. Original JMB paper, looking at cooling induced modulation of crystal packing
   
2. Review on cryocooling in Quartely Reviews of Biophysics
3. Paper looking a the reversibility of cooling by cycling beta-galactosidase crystals between LT and RT.
4. Measurements of solution thermal contractions, and discussion of cryoprotection optimization.
   

These results led to additional experiments to investigate why cooling induced lattice damage can sometimes be recovered by warming the crystal to room temperature and then recooling. This appears to work, at least in part, via the transport of water into or out of the crystal, altering the thermal contraction properties of the bulk solvent to better match the contraction of the interstitial space. This paper is here:

• Solvent transport and annealing
  

We are continuing this work by carrying out X-ray diffraction experiments on various protein crystals in concert with bulk measurements on the thermal contraction of solutions of water and various cryoprotective agents.