reminds me of structure 1NEU, although here the gelation was reversible, see ref and abstract below - the paper has a photo of a tube of soluble protein and gelled protein
we have also had a couple of cold-sensitive proteins in our hands, that precipitated at 4 degrees when concentrated, but were soluble at room temp to quite high concentrations (and we got structures for both) Neuron. 1996 Sep;17(3):435-49. Crystal structure of the extracellular domain from P0, the major structural protein of peripheralnerve myelin. Shapiro L, Doyle JP, Hensley P, Colman DR, Hendrickson WA. P0, the major protein of peripheral nerve myelin, mediates membrane adhesion in the spiral wraps of the myelin sheath. We have determined the crystal structure of the extracellular domain from P0 (P0ex) at 1.9 A resolution. P0ex is folded like a typical immunoglobulin variable-like domain; five residues at the C-terminus are disordered, suggesting a flexible linkage to the membrane. The requirements for crystallization of P0ex are similar to those for maintaining the native extracellular spacing of adjacent myelin lamellae; thus, given the self-adhesive character of P0ex, the crystal itself may reveal some of the natural interactions that occur between P0 molecules in myelin. The structure leads to the suggestion that P0 extracellular domains may emanate from the membrane surface as tetramers that link to tetramers on the opposing membrane surface, to result in the formation of networks of molecules. We report analytical ultracentrifugation data for P0ex that support this idea. PMID: 8816707 On 23 Apr 2013, at 00:36, Pascal Egea wrote: > 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
