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Hi Subbu, I had a similar problem when forming a complex of protein and DNA. The change in charge on the surface of the complex with respect to that of the protein alone caused precipitation. This was overcome by adjusting the pH of the buffer. One could try screening different pHs and salt concentrations. Good luck! Dave -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of N. Ramasubbu Sent: 26 September 2006 16:27 To: ccp4 Subject: [ccp4bb]: Problem with crystallizing a complex of two proteins *** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.ccp4.ac.uk *** Hi all: I am trying to crystallize a complex of two proteins by mixing equal concentration of the two. At equimolar ratio or at 10mg/mL, for example, I get a precipitate right away after mixing. These two form a tight complex and even in other experiments using gel filtration we have seen precipiatation and when run on a gel, we see two bands with appropriate molecular masses. Molecular weight of one is around 56 kDa and the other one is 20kDa. I would like to know of methods that one could try to keep the complex in solution so that it can be crystallized. Both are highly soluble proteins and can be crystallized individually with out any difficulty. Both form crystals using MPD at about 40%. Any help would be realy appreciated. Thanks a lot subbu
