Hans, Most natural toxins from snakes, scorpions etc are 50+/-some peptides. And quite a few of those have been studied and crystallized (see pdb for a list). Having worked on one of these structures as a graduate student, I can share my experience: - Purification is harder than you would think. You are talking about < 10kD, usually around 5kD. Many methods (size exclusion, even concentration over a simple membrane) don't work as easily as you would like. - I did not have much of a problem crystallizing (i.e. no worse than other proteins, maybe even a little easier) - Crystals tend to diffract well (maybe better than average) - Structures can be hard to solve; MIR is very difficult because ions tend to not go into such crystals easily (because the molecules are small and tightly packed?); MR is hard because (again) it does not work very well on very small systems - Crystallization is not necessarily purification - if you have a mixture of peptides to start with, it may be harder to crystallize, or not: you might get a crystal that is a (random-ish) mixture. - If you have more than two cysteines in your sequence (natural toxins typically do), the additional problem is to get the correct folding and disulphide bridges; alternatively it is very hard to discriminate between correctly and incorrectly linked disulphides
Finally: These sequence should be small enough for NMR. That may or may not answer your questions, but it avoids your original question. Mark -----Original Message----- From: H. Raaijmakers <hraaijmak...@xs4all.nl> To: CCP4BB <CCP4BB@JISCMAIL.AC.UK> Sent: Thu, Nov 10, 2011 8:16 am Subject: [ccp4bb] crystallization of synthetic peptides Dear crystallographers, Because of the low cost and speed of synthesizing 40- to 60-mer peptides, I wonder whether anyone has (good or bad) experiences crystalizing such peptides. In literature, I've found up to 34-mer synthetic coiled coils, but no other protein class. I can imagine that a protein sample with a few percent "random deletion mutants" mixed into it won't crystallize easily, but has anyone actually tried? cheers, Hans
