Blob one is something possibly distorted by alternate partial occupancy binding sites near a symmetry axis. Blob 2 could be a chloride ion, or if that is not enough density, maybe bicarbonate. Blob 1 seems to be attracted two His residues, of the things in your mixture, Mg(II) seems possible or Cl-. Blob 2 is less likely to be metal around those Arg residues, but Cl- or bicarbonate are possible and well-known in this kind of coordination environment. Cl- is in your mixture, and bicarbonate can accumulate, especially at alkaline pH from atmospheric CO2.
Cheers, Roger Rowlett On Oct 2, 2017 6:06 PM, "Lucas" <lucasbleic...@gmail.com> wrote: I'm in the later stages of solving a structure which contains two tetramers in the asymetric unit. I found these two blobs (in equivalent positions on each tetramer) with positively charged residues around it. Crystallization condition is Magnesium chloride, Bis-tris and PEG3350. While the second blob looks like a metal, the first one has a weird shape even though they are expected to have the same thing. Any ideas? Lucas
