Hi all, My google-fu has failed me once again so I am turning to the collective knowledge of the bb. I'm working on a blobology challenge at the moment and have hit a wall. Is anyone aware of an ion that coordinates to lysine and prefers octahedral geometry. The mystery ion seems to have perfect octahedral geometry with bond distances of ~2.1 angstrom, but the only direct side chain interaction is to a lysine NZ, the rest are waters.
I've been through the various and sundry metal coordination resources including the Harding website and the Minor paper on datamining metal binding sites. These unsurprisingly indicate that a cation is unlikely, especially in the absence of any other, more coordination friendly side chain or backbone atoms. I manually attempted chlorine but the density said no. I have this protein in four other space groups, many from the same batch of protein, and none of them have similar density at this residue so it isn't a covalent modification. I have Mg, Na, and Cl in the crystal solution/storage buffer, but as mentioned above the cations don't make chemical sense and chlorine was a no go. I'm not ruling out an adventitious tag-along. Any suggestions would be appreciated. Thanks for your time, Katherine -- "Nil illegitimo carborundum"* - *Didactylos
