I have seen this in MnSOD. We had a tetramer in the ASU and each active site had different ligands in our peroxide soak. I assumed the crystal lattice can influence these things or it is inappropriate metal incorporation. I would highly recommend doing ICP-MS on a dissolved crystal and on your purified metalloprotein to make sure your metal incorporation is 100% the metal you want.
On Wed, Nov 29, 2017 at 1:58 AM, <herman.schreu...@sanofi.com> wrote: > Dear Denis, > > > > I would first superimpose both monomers to see if you can find a reason why > one subunit has a bound water and the other not, which would in general be > flanking side chains in (slightly) different positions. Next I would look > for some global differences between the subunits that could be linked to > crystal contacts explaining the non-random distribution of the subunits. > However, these differences might be quite subtle and difficult to detect. > > > > As Emily suggested, you could also do some functional assay’s to see if > there is any positive (or negative) cooperativity between the subunits > providing independent support for functional differences between the > subunits. > > > > My 2 cts, > > Herman > > > > > > Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Denis > Rousseau > Gesendet: Dienstag, 28. November 2017 20:04 > An: CCP4BB@JISCMAIL.AC.UK > Betreff: [EXTERNAL] [ccp4bb] Differences in a homodimer protein > > > > Hi BB members > > > > I have a homodimeric protein, which contains metal centers. In several > different derivatives I find a water molecule on a metal center in one > subunit which is absent on the other. It is always the same subunit that > contains the water molecule. The resulution is ~2.4 A. Is this an artifact > or a functional difference? If it is truly homodimeric I would expect > differences to be random. The space group is P212121. > > > > Thanks for the advice. > > > > Denis Rousseau > > ________________________________ > >
