Hi All, I want thank everyone who replied to my request on Fab:peptide crystallization. I received wonderful advice from all of you and it was very helpful in that I did get some beautiful crystals in my screens! Whether or not there is peptide bound is another matter..:). In case anyone of you are interested I prepared my Fab:peptide complex as follows: I first dissolved my peptide in 100% DMSO at a stock concentration of 100mg/mL (this peptide a very high solubility in DMSO!). I added enough peptide to my protein to give me a 10:1 peptide:protein molar ratio and a final DMSO concentration of ~2%. I did not see any precipitate after addition of peptide to protein nor after subsequent centrifugation This was a promising observation in that when I did a mock set up of peptide in the same volume of the same buffer as protein but without protein I saw very visible precipitate after addition of peptide. This suggested to me that a significant portion of peptide bound to the protein and reducing free peptide to a reasonable concentration so as to remain in solution possibly? I used this protein:peptide mixture to set up screens and of course the rest is history. Thanks again everyone!
Christine
