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Cryo Trouble? Give the following tips a try next time your crystal is fussy about freezing.
Try X-ray data collection at room temperature.
Evaluate other cryoprotectants. Try CryoPro from Hampton Research, which contains 36 unique cryopreservation reagents.
For more information visit http://hamptonresearch.com/product_detail.aspx?cid=30&sid=189&pid=30
Mixing of different cryoprotectants can have a superior protective effect over single component cryoprotectants of the same total concentration.
Change the rate of cooling.
a) Accelerate the rate of cooling. The fastest cooling rates have been achieved by blowing off the gas layer on liquid nitrogen during plunge cooling. (Hyperquenching for protein cryocrystallography, M. Warkentin et al, J. Appl. Cryst. (2006). 39, 805-811)
b) Slow the rate of cooling. Perhaps better suited to crystals with smaller solvent channels. The key to successful slow cooling of protein crystals is to carefully and completely remove all of the solvent from the surface of the crystal using oil such as Paratone-N, Perfluoropolyether, Mineral, Silicon, NVH or other. Remove ALL of the liquid from the surface of the crystals when using oil. (Slow cooling and temperature-controlled protein crystallography, Warkentin et al 10.1007/s10969-009-9074-y and Slow cooling of protein crystals, Warkentin et al, Volume 42, Part 5, Pages 944-952, October 2009) For more information visit http://hamptonresearch.com/menus.aspx?id=3&sid=138
Using salt as a crystallization reagent? Many salts are cryosalts, including malonate, formate, citrate, tartrate, acetate, Tacsimate and other organic acids, ammonium sulfate (>3.5 M), lithium sulfate, lithium chloride and other alkylammonium salts. For cryo try increasing your salt concentration by 20%. (Cryosalts: suppression of ice formation in macromolecular crystallography, K. A. Rubinson et al, Cryosalts: suppression of ice formation in macromolecular crystallography.
Try the identical cryo procedure again with another crystal.
Vary the time and temperature of the crystal handling steps.
Check the liquid nitrogen level in your dewar and maintain a consistent level, day to day, week to week, month to month, year to year.
Try annealing. (Macromolecular crystal annealing: Techniques and cases studies. Bunick et al, The Rigaku Journal Vol. 15/ number 2/ 1998 and Macromolecular crystal annealing: overcoming increased mosaicity associated with cryocrystallography, Harp et al. (1998). Acta Cryst. D54, 622-8
Match the osmotic pressure of your cryoprotectant to the osmotic pressure of the reagent producing the crystal. Crystallization reagents with lower salt concentrations require a higher percentage of cryoprotectant for cryo protection than crystallization reagents with higher salt solutions (Cool data: quantity and quality. Elspeth Garman. Acta Cryst. (1999). D55, 1641-1653.). Osmolality tables (Weast, R. C. (1988-1989). Editor. Handbook of Chemistry; Physics, 69th ed. Boca Raton, Florida: CRC Press) can be used to estimate the osmolality of reagents. Another trick is to slowly concentrate a drop of the mother liquor by leaving the drop open to air and allowing the drop to slowly dry down, checking the mother liquor for clear glass freeze every few minutes. If you do not have X-rays to check for clear glass freeze, you can guesstimate by carefully placing the dewar under a dissecting microscope with overhead lighting. Focus on the surface of the liquid nitrogen, and bring the cooled loop into view just above the surface of the liquid nitrogen, where it is cold enough for guesstimate freezing.
Try high pressure cooling. (High-pressure cooling of protein crystals without cryoprotectants, Kim et al, Acta Cryst. (2005). D61, 881–890)
Cryoprotection of delicate crystals - Artem Evdokimov's humble recipe.
http://www.xtals.org/crystal_cryo.pdf
Two words. Liquid propane.
http://cars9.uchicago.edu/biocars/pages/flashcooling.shtml
Roger S. Rowlett's Cryoprotectant Strategy
1. Transfer crystals to mother liquor plus 30%v/v glycerol or ethylene glycol (sometimes lower depending on crystallization
reagent).
2. Transfer crystals to mother liquor plus 30%w/v glucose (or try sequential soaks in mother liquor plus 15%w/v and then 30%w/v glucose. Just a few seconds or minutes is usually enough). Glucose or other sugars often work when glycerol or ethylene glycol fails.
3. Try the "no-fail" in situ cryo method, which is a gradual buildup of cryoprotectant. This method is especially appropriate for crystals that cannot tolerate direct transfer to cryoprotectant solution, or for crystals that are especially sensitive to concentration changes in the mother liquor driven by drop evaporation. In our laboratory this method is routinely used with success on otherwise very sensitive crystals. This particular method is adapted for hanging drop crystallization. Ligands can be soaked in at the same time as cryopreservation if included in the cryoprotectant solution at 125% of the final, desired concentration.
a) Prepare a solution of artificial mother liquor plus 30% w/v glucose (40% v/v glycerol or another cryoprotectant can be substituted)
b) Remove a coverslip containing a drop with crystals to be cryoprotected and add 0.25 drop volume (DV) of cryoprotectant solutions (e.g. for a 4 uL drop add 1 uL of cryoprotectant solution). Replace coverslip on well and let stand for 5 minutes. Examine the crystals for cracking and/or dissolution.
c) Repeat the previous step with the following additional cryoprotectant additions: 0.25 DV, 0.50 DV, 1.00 DV, 2.00 DV. After each addition replace the coverslip over the well and let stand for 5 minutes. Examine crystals for cracking and/or dissolution.
d) After the last addition and 5 minute incubation, remove coverlip, fish out crystals with mounting loops and freeze directly in liquid nitrogen. The final glucose concentration will be 24%, sufficient to protect most crystallization solutions from ice formation upon freezing in liquid nitrogen.
This is very gentle, and often works when #1 and #2 does not, but in our hands nearly always increases mosaicity. (But mosaic is better than no diffraction.)
4. Try dragging crystals though Paratone-N to remove surface water from the crystal. This actually nearly always works for us, but is more fussy than #1 or #2, and it is easier to damage crystals during manipulation because of the viscosity of the oil.
I normally plunge protected crystals into liquid nitrogen after mounting.
Ice rings are a good indication of poor cryoprotection, but lack of diffraction could just be your crystals, too. For our latest dataset, we just sorted through 38 crystals until we found a good one. The key, as it turned out, is that all of our beautiful large crystals were apparently difficult to visualize disordered stacks of plates (we didn't notice this until some fractured during cryo-soaks) whereas some of the small crystals were actually single crystals. We selected a decently diffracting small one and took loooooooooooong frames to get a good data set. (Roger S. Rowlett, Professor, Colgate University Presidential Scholar, Department of Chemistry, Colgate University, NY, USA)
Dig around in the cryoprotectant database for ideas. http://idb.exst.jaxa.jp/db_data/protein/search-e.php
Try 10% glycerol. (Jim Pflugrath)
Try 10 to 20% 2,3-butanediol. It can also reduce mosaicity. Try a quick dip, 30 to 60 seconds.
Fine tune the cryo concentration by screening 2.5% concentration increments, dipping a loop in the cryo buffer, freezing it and collecting X-Ray diffraction data to find the minimum concentration required that produces a clear glass and no ice rings.
Look back in your screen plates for a different crystal in different reagent, do not pass go, do not collect $200.00 and start over at the top of this tip.
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