I have experienced a similar thing with lysozyme immediately forming a clear gel when attempting to dissolve at high concentration in D2O. The clear gel did not readily dissolve on dilution (in D2O) and I discarded it. I later made the sample by dissolving in H2O and dialysing to D2O.
Another protein I have worked with, a multimeric ATPase, requiring ATP to assemble, forms a white gel when prepared in isolation from other proteins of its complex and ATP is added. From memory, the gel formation is fast (minutes) at higher concentration (~20mg/ml), and slow (hours to days) at lower concentration 1-5mg/ml, but this formed a precipitate not a gel. Presumably this was a polymerisation. The white gel was resistant to dilution or addition of salts. After baking, I find that meat juices cool to form a gel, transparent and optically clear. Like gelatine. Sincerely, Anthony Anthony Duff Telephone: 02 9717 3493 Mob: 0431891076 -----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Michael Thompson Sent: Tuesday, 23 April 2013 9:44 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] gelification of a pure protein Does your protein have multiple exposed Cys residues? I have observed this before with a protein I worked with that had many exposed Cys residues. In my case I could add more DTT and minutes later the gel would be completely dissipated. My hand-wavy explanation was that the protein stays folded but becomes highly crosslinked when concentrated and exposed to air. I did have some small amount of DTT in my buffer to start with, but I assume it became oxidized relatively quickly (as DTT does), leaving my protein thiols to go wild and make S-S bonds between themselves. Good luck, Mike ----- Original Message ----- From: "Pascal Egea" <pas...@msg.ucsf.edu> To: CCP4BB@JISCMAIL.AC.UK Sent: Monday, April 22, 2013 3:36:24 PM GMT -08:00 US/Canada Pacific Subject: [ccp4bb] gelification of a pure protein Dear All, I am presently faced with a peculiar case in the lab. We are expressing a protein in E. coli and we are able to express it as a fusion protein without problems . Fusion cleavage goes well and the final product looks homogenous by size-exclusion chromatography with the expected molecular weight. There are no signs of aggregation. However when we lower the salt concentration by dialysis then the protein forms a gel. transparent , optically clear, with no fluffy material (in the cold room). Gelification seems to occur when we lower the concentration below 100 mM NaCl. This protein has a fairly high pI (~9.0). Attempts to reverse the process by gentle heating or salt addition have been so far unsuccessful. It is not a thermophilic protein. We have not been able to obtain crystals so far. Has anyone already observed this kind of behavior and/or have any suggestions? Many thanks in advance . -- Pascal F. Egea, PhD Assistant Professor UCLA, David Geffen School of Medicine Department of Biological Chemistry Boyer Hall room 356 611 Charles E Young Drive East Los Angeles CA 90095 office (310)-983-3515 lab (310)-983-3516 email pe...@mednet.ucla.edu -- Michael C. Thompson Graduate Student Biochemistry & Molecular Biology Division Department of Chemistry & Biochemistry University of California, Los Angeles mi...@chem.ucla.edu
