Artem,

In addition to other answers, one of the more esoteric (but surprisingly effective) ways to destroy the protein 'skin' on drops is to add a tiny bit of Trypsin solution.

Will you go a bit further and say what exactly you mean by "a tiny bit of Trypsin solution"? :-) What is the composition of your successful trypsin solution? In what volume do you add it? Do you add it right on top of a sitting or hanging drop? Was your situation one in which the skin and crystals were fused? Was there a rationale for why you used trypsin as opposed to other peptidases (I imagine it's what you had on hand ...)?

Emily.

Crystals generally tend not to be affected, but (at least in my experience) the protein skin dissolves within a couple of hours or less. In at least one case, this was the only way to get rid of skin, which otherwise tugged on crystals and resulted in considerably worse diffraction.

Good luck,

Artem

P.S. needless to say, if your skin is made of something else then trypsinolysis won't work :)

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On Wed, Feb 25, 2015 at 2:34 AM, Ulrike Demmer <[log in to unmask]> wrote:
Dear crystallographers,

I am trying to crystallize a soluble protein which tends to form aggregates. The crystallization condition is 20% PEG 3350 + 0,2 M Na-Formate. During the crstallization process a thick skin is formed on top of the sitting-drops. As well the crystals are buried in precipitate. Before I start harvesting I try to remove the skin but still it is hardly possible to get any crystals out of these drops.

Any suggestions how to avoid the formation of skin on crystallization drops ?

Cheers,

Ulrike