by Peter Nollert
December 16, 2009 02:19
Taking a wrong turn while hiking the great outdoors can be the start of a big adventure, but in the protein crystallization lab it usually means a waste of time, especially when dealing with optimizing protein crystallization hits. The critical point is a typical go/no-go decision where the question you need to answer is this: is it worthwhile to follow up on this particular crystallization experiment? The answer is "yes" if there are no other, potentially better crystallization hits and if you're sure that the objects you're looking at are protein crystals, though not yet useful for X-ray diffraction experiments. The result of a positive decision will be committing to an often tedious protein crystal optimization project, possibly weeks of re-purification and preparing numerous small variations of that protein crystallization setup.
At this point there's one very simple observation that you can make to avoid taking a wrong turn: check the reservoir solution for crystals. Any crystals there resemble those in the drop?
Since many crystallization cocktails are formulated with high salt concentrations, just a little dehydration can cause salt crystals to form.
So, if there are crystals in the reservoir you're very likely dealing with salt crystals in your drop and not the sought-after protein crystals. Don't take this turn and keep on searching for a better protein crystallization hit.
Good reasons to curb your enthusiasm: crystals in the reservoir solution of (A) hanging drop protein crystallization experiments or in (B) sitting drop protein crystallization setups are a harbinger of bad news: salt crystals.
Bon voyage,
Peter