by Peter Nollert
September 18, 2009 06:00
Protein crystallization via vapor diffusion setups is by far the most commonly used crystallization technique. But which format? Hanging drops or sitting drops?
The BMCD shows that many researchers favor hanging drops: I found 9,083 entries for "hanging", and 1,534 for "sitting" drops (search results using a famous search engine confirmed this trend with 4.7:1). While sitting drops are simple to prepare by hand and by robots, hanging drops are more challenging to set up. There are several advantages though when dealing with hanging drops: often the protein crystals don't stick to the surface and collect in the middle of the drop. On the other hand, some dexterity is required when you flip the drop for harvesting protein crystals with a loop. These and many more reasons have split crystallizers into two factions, each claiming that hanging drops are better than sitting drops and vice versa.
And now guess what - you can have it both!
The Kim lab has just published an ingenious protocol to get the best of two worlds (Whon et. al., J.Appl.Cryst., 42, 975-976 "A simple technique to convert sitting-drop vapor diffusion into hanging-drop vapor diffusion by solidifying the reservoir solution with agarose"):
1. prepare sitting drop crystallization experiments in a protein crystallization tray
2. add agarose solution to reservoirs and let solidify
3. incubate, image and harvest upside down or downside up - as you whish.
A solid reservoir solution.
How simple is that?
Figure: (B) Hanging sitting drop and (A) sitting hanging drop.
BTW - this format should also be a nice way to transport 'living crystallization experiments' without the reservoir solution splashing into the crystallization drops.
Simple does it,
Peter