Hi Jobi- You might want to try using drop ratios ---we have had great success with this many times. My favorite "additive screen" is using the Hampton Research Crystal Screen HT as an additive screen. I usually start by adding 5% to the well---this has often yielded good crystals where the traditional 96 reagent additive screens and the detergent screens do not.
Good Luck! Annie From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jobichen Chacko Sent: Wednesday, April 13, 2011 5:44 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Crystal Optimization Dear All, We got crystals for a 35 KDa protein with 323aa including His tag and linker. It was originally crystallized in 0.1M BisTris Propane pH:6.5, 0.2M Potassium thiocyanate and 20% PEG 3350. Later we managed to obtain crystals with 0.1M BisTris pH:6.5, 0.2M Potassium thiocyanate and 20% PEG 3350 as well. Crystals are 3 dimensional in shape and 0.2-0.3mm long. Maximum resolution obtained till now is 5.8Å. Tried various cryo conditions like Oil, glycerol, salt and sugars. However, the resolution hasn't improved. The crystal tends to break in the presence of glycerol. Kindly give your suggestions to improve the resolution. Thanks. Jobi
