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It's hard to see clearly the density, but judging from the abundance of carboxy groups, it may be a metal. Maia Daniel Bonsor wrote: > Hello again > > I currently have some unexplained density in my structure. As you can hopefully see from the images (see file), the density is dumbbell shaped. Whatever it is, it is coordinated by Asp and Glu residues. To me it looks like each lobe is a ring structure. > > > The crystallization condition was: > 6.5% PEG 8K, 10mM ZnSO4, 100mM sodium cacodylate pH 6.5, 100mM Am2SO4, 1% glycerol, with 20% glycerol as cryo. > Protein was originally in 50mM Tris, 50mM NaCl pH 7.5. > > > I originally placed a single Zn at the center of each lobe. Though after refmac, the Zn was displaced to one side. Two zincs in each dumbbell may have worked, but I am dubious about two zinc atoms being 4A apart and there is still some unexplained density. Are there any possible cyclization reactions of Tris, cacodylate or glycerol may have undergone to explain the density? Or is it simply a highly ordered water network? Or is there some other explanation? > > Thanks in advance > > Dan > > > ------------------------------------------------------------------------ >