Just a thought, Mary - going back to your original question about MPD. I extracted the crystallization conditions from REMARK 280 of 3939 PDB entries a couple of years ago. The average concentration of the MPD used was high - 38.6%, while PEGs tended to be used at lower concs, e.g. PEG400 25.7%. You can see the data at www.douglas.co.uk/top14.htm
I thought this information could be useful if you want to replace some of the MPD with another precipitant (or cryoprotectant). Best wishes Patrick Shaw Stewart -- [EMAIL PROTECTED] Douglas Instruments Ltd. DouglasHouse, EastGarston, Hungerford, Berkshire, RG177HD, UK Directors: Peter Baldock, Patrick Shaw Stewart, James Smith http://douglas.co.uk or http://www.douglasinstruments.com Tel: 44 (0) 148-864-9090 US toll-free 1-877-225-2034 Regd. England 2177994, VAT Reg. GB 480 7371 36 > -----Original Message----- > From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Mary > Fitzgerald > Sent: 09 July 2007 23:05 > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] Help with reducing crystal mosaicity > > Help please! > > I'm looking for some new ideas. I have crystals that come out of a > sitting drop with a mixture of sodium cacodylate at pH 6.5, magnesium > acetate and MPD for the well solution. The MPD concentration is > sufficient to act as a cryoprotectant. Currently, I directly freeze > these crystals in liquid nitrogen. When I collect data, I typically > have high anisotropic mosaicity; it ranges from 0.8 to 1.2. This is > further complicated with a weakly diffracting crystal (4-5 A) that has > a long unit cell axis of ~500 and often twinning. > > It has been suggested to me that the cryoprotectent is a problem. I > haven't checked the diffraction at room temperature, yet. Please no > suggestions of finding a different crystal form as that's not a > consideration at the moment. I have my reasons. I did find one > crystal that has lower mosaicity (0.5 to 0.8) but had weaker > diffraction then the typical crystal. Attempts at flash cryoannealing > have not helped. > > So, what's a good way to change the cryoprotectant if the > cryoprotectant is the precipitant? I've considered trying dehydration > but wasn't certain if that would help with the mosaicity. > > Thanks for any ideas, > > Mary X. Fitzgerald > Postdoctoral Associate
