Dear Ulrike, you could try avoid the drop-air interface by overlying sitting drops with silicone oil or a 50/50 silicon/paraffin oil mixture. Note that this will alter the kinetics with which your drops reach equilibrium, and hence may alter your ability to get crystals of the protein. Batch crystallization under oil is another option of course.
Adding some alcohols (5-10% EtOH, isopropanol) or detergent (0.5 mM LDAO for example) in your crystallization conditions may also be something to consider. If none of these work, I'd concentrate on harvesting the crystals from the skin. I tend to cut these open from the side, flip over the skin so that one has better access to the crystals that generally are associated with the inner face of the skin. You can try peel the crystals off the skin, or cut out a piece of skin surrounding a crystal. That will not hurt diffraction quality of the crystals. Hope that helps. Han On 25 Feb 2015, at 09:34, Ulrike Demmer 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 Han Remaut, PhD Laboratory of Structural & Molecular Microbiology VIB / Vrije Universiteit Brussel Building E4, Pleinlaan 2 1050 Brussel han.rem...@vib-vub.be tel. +32-2-629 1923 / +32-499 708050 http://www.vib.be/en/research/scientists/Pages/Han-Remaut-Lab.aspx
