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Don't forget that your SeMet has real differences from your native - the S to Se brings in 18 extra electrons (less obviously if there is lower incorporation). But that mean if your native is isomorphous enough (you didn't say) then you possibly have 'ordinary' isomorphous differences to work with. You could then work in the anomalous as a sort of SIRAS solution. SeMet as isomorphous has been used previously in many structure solutions. All the best Martyn Martyn Symmons Cambridge ________________________________ From: vijay srivastava <[log in to unmask]> To: [log in to unmask] Sent: Tuesday, 3 June 2014, 9:37 Subject: [ccp4bb] experimental phasing at low resolution Dear All, Does anyone know of a facility that provides amino acid analysis for determination of SeMet incorporation in a recombinant protein? We're looking for some advice about how to proceed with a structure we're working on. Our protein is 350 amino acids (10 methionine are present) and naturally binds magnesium. We have a SeMet data set at peak that goes down to 5.4 angstroms. We tried to find the heavy atom position with Shelxcde program. The log file is given as below. Resl. Inf - 8.0 - 6.0 - 5.6 - 5.4 - 5.2 - 5.0 - 4.8 - 4.6 - 4.4 - 4.2 - 3.98 N(data) 529 643 241 29 0 0 0 0 0 0 0 <I/sig> 63.5 19.5 10.6 10.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 %Complete 94.1 98.9 99.2 18.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 <d"/sig> 3.06 1.24 1.07 1.21 I am also attaching the .lst and .res file and from that we were considering that only one selenomethionine position.We have one monomer per AU (-unfortunately, MR is not working for this project). The space group is P3 . We also have a native set down to 3.4 angstroms. While we understand that we may need more phasing information we're wondering if anyone might have some other suggestions or insights about how we can move forward given the data that we currently have. Can we extend the phases with our native data set. Thanks in advance for any advice. regards Vijay