i am trying crystallization of a small protein and got sufficient number of hits. These crystals has a rod shape morphology with length around 0.7-0.8 mm, however, the width is just 0.05 mm (i want to diffract these using home source instrument). any suggestions about how can i increase the width of these crystals? Can i change crystal morphology keeping the crystallization condition same?
Try to reduce the rate of crystal growth by lowering temperature, protein concentration, and precipitant concentration.
You could lower the protein concentration like Ho suggested and try streak seeding. Playing with the pH might help sometimes also.
Have you tested your crystals for diffraction already? In other words are you sure that the needle-like morphology is a problem? Sometimes such crystals diffract fine.
If you want to change the morphology, the idea is to play with the molecular contacts within the crystal lattice, preferably those in the dimension that gives length to your crystals. Changing such interactions can be done in many ways like suggested by others. Adding small molecules (additives) to your existing condition is another way - e.g. there are additive screens available.
Good luck!
Thank you all for your valuable suggestions.
Dear Tjaard Pijning,
Yes the do diffract but with poor resolution. However, the signal mutant crystal of same protein in same condition has really good dimensions (0.8 mm length and 0.5 mm width) and it went to 1.2 angstrom. i do have tried most of the commercially available conditions and additives and i think this is the best condition. I am just hooping for high resolution now. i do have tried different cryoprotectant and PEG 400 was best.
Dear Vishal,
Changing the crystal growth habits is difficult. There was an interesting research published over the years with limited results. Two directions that emerged is to try different metal ions to influence the morphology. Also people tried macro seeding additives as well as additional components of the crystallization media like other proteins that might very weekly interact with your protein and organize it differently. All of these methods are slow and labor extensive. There are no easy solutions.
However, in my hands if the protein crystallizes in one condition there is a huge chance that it crystallizes in other conditions too. Try more screening. Your needle like morphology comes from the speed of growth of a particular direction, according to research done by Peter Vekilov in Houston.
Good Luck.
Bog
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