The better your initial, experimental map is, the more model you will be able to build confidently into this unbiased map before proceeding to phase combination. MAD phases result from perfectly isomorphous data, and do not detoriate at low resolution as do MIR phases. MIR phases, on the other hand, provide superior phasing power at low resolution resulting in better connectivity. Not surprising, the best maps we every have seen were eitehr MAD or combined MIR-MAD maps. The following maps are nice examples for quite exceptional quality experimental maps. Click on the map icons to get a full gif image.
Panel 1 Region of exceptional experimental electron density map created from multi-wavelength data collected at the ALS. Only solvent flattening and density modification have been performed. No phase combination with any model phases has taken place. Panel 2 : .to show the excellent correspondence with actual protein residues, a previously determined molecular replacement model of Arg has been placed into the electron density. The model can be unambiguously and easily built into the electron density. Panel 3 : View is a cross section of the apoE four helix bundle. The empty space in the centre of helix one and two is clearly visible. Panel 4: : to show the excellent correspondence of experimental electron density with actual protein residues, model helices have been placed into the electron density. Experimental phases had an average figure of merit of 0.86. There is very little noise and excellent connectivity in the electron density.
Panel 1 : Exceptional experimental electron density map created from multi-wavelength data collected at SSRL beamline 1-5 on a Gold derivative of tetanus C fragment. Only solvent flattening and density modification have been performed. No phase combination with any model phases has taken place. Panel 2 : tyrosine residue fitted into experimental electron density. Notice the hole of which is frequently proudly presented by crystallographers in REFINED structures as a indicator of quality and resolution - here you see the same in EXPERIMENTAL phases! Panel 3 electron density of combined MAD/MIR map in tetanus C fragment.
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This World Wide Web site conceived and maintained by Bernhard Rupp. Last revised Dezember 27, 2009 01:40