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Dear CCP4 Community, My apologies for the off topic question to the bb. I am trying to crystallise a small protein-protein complex. I purify as a complex protein after expression in BL21DE3 cells through NI-NTA affinity chromatography. pI of one of the protein is around 10.6 where as another component have 4.0. I am in the screening stage of the crystallisation. During crystallistion process it precipitate very quickly as i add the protein into the crytallisation solution drop. This happens in almost all the condition of the hampton INDEX and crystal screens. I purify this complex in Tris-Cl buffer at pH=8.0. it is happily soluble and donot prcipitate at this pH in the same buffer. I can concetrate this protein upto ~10-15mg/ml. could any one suggest the solution, that will be most appreciatable. Thanks in advance Ron