Hi Bernhard, It is difficult guess with two dimensional images. Is it possible a metal coordinated by Cys-Sulfur and one or two acetate ions?
HTH, Partha Sent from my iPhone > On Aug 19, 2014, at 10:12 AM, Bernhard Loll <[email protected]> wrote: > > Dear all, > > We are currently working on a small GTPase. The structure has been solved to > 1.4 A with two molecules in the ASU. In the difference electron density we > can clearly see difference density (in one monomer) attached to a Cys residue. > > The protein has been expressed in E. coli. For crystallization experiments > the GTPase was incubated with GMPPNP, that had been dissolved in 20 mM HEPES > pH 7.5 and 50 mM NaCl. Prior to crystallization > the protein was stored in a buffer composed of 20 mM HEPES pH 7.5, 200 mM > NaCl, 5 mM, Mg acetate, 2 mM DTT and 2% (v/v) glycerol. > > The protein crystallized under the following conditions: > 28% (v/v) PEG 200, 5% (w/v) PEG 3000 and 100 mM MES buffer at pH 6.0 > > The anomalous signal is too weak to judge the positions of the sulphur atoms. > We have performed MS analysis on the protein before crystallization and on > dissolved protein crystals. MS revealed a mass difference of about 135 Da, > indicating that some chemistry must have went on in the crystallization drop. > > The extra electron density has a planar shape and is quite symmetric. We have > placed some dummy water molecules in the density. Distances are given in A in > the PNG file. > > Attached files > > coot1.png: 2FoFc electron density map (blue) @ sigma=1 and FoFc electron > density map (blue) @ sigma=+3 after phenix.refine > coot2.png: same electron densities as in coot1.png, with dummy atoms placed > coot3.png: same electron densities as in coot1.png, side view > > Thanks for your time and efforts. > > Cheers, > > Bernhard > -- > Dr. Bernhard Loll > Freie Universitaet Berlin > Fachbereich Biologie, Chemie, Pharmazie > Institut fuer Chemie und Biochemie > AG Strukturbiochemie > Takustr. 6 > D-14195 Berlin > Germany > > Phone: +49 (0) 30 838-57348 > Fax: +49 (0) 30 838-457348 > Email: [email protected] > Homepage: http://www.bcp.fu-berlin.de/chemie/bc/ag/agwahl/ > <coot1.png> > <coot2.png> > <coot3.png>
