Begin forwarded message:
Date: June 6, 2012 3:05:16 PM EDT To: aaleshin <aales...@burnham.org<mailto:aales...@burnham.org>> Subject: Re: [ccp4bb] Fun Question - Is multiple isomorphous replacement an obsolete technique? There are four such papers in Methods in Enzymology, Vols 368 and 374: David Blow: How Bijvoet Made the Difference: The Growing Power of Anomalous Scattering V. 374, pp. 3-22 Brian Matthews: Transformations in Structural Biology: A Personal View V. 368 pp. 3-10 Michael Rossmann: Origins V. 368, pp. 11-21 Ulrich W. Arndt: Personal X-ray Reflections V. 368, pp. 21-45 These reminiscences are there entirely because my co-Editor Bob Sweet felt exactly the same way Alex does. Charlie On Jun 6, 2012, at 2:12 PM, aaleshin wrote: I wonder if anyone attempted to write a historic book on development of crystallography. That generation of crystallographers is leaving this world and soon nobody will be able to say how the protein and non-protein structures were solved in those days. Alex On Jun 6, 2012, at 8:48 AM, Gerard Bricogne wrote: Dear Fred, May I join Phil Evans in trying to dissipate the feeling that anomalous differences were fictional before flash-freezing and all the mod cons. I can remember cutting my teeth as a PhD student by helping Alan Wonacott with the experimental phasing of his B.St. GAPDH structure in 1973-74. The data were collected at room temperature on a rotating-anode source, using film on an Arndt-Wonacott rotation camera (the original prototype!). The films were scanned on a precursor of the Optronics scanner, and the intensities were integrated and scaled with the early versions of the Rotavata and Agrovata programs (mention of which should make many ccp4 old-timers swoon with nostalgia). Even with such primitive techniques, I can remember an HgI4 derivative in which you could safely refine the "anomalous occupancies" (i.e. f" values) for the iodine atoms of the beautiful planar HgI3 anion to 5 electrons. This contributed very substantially to the phasing of the structure. In fact it would be a healthy exercise to RTFL (Read The Fascinating Literature) in this area, in particular the beautiful 1966 papers by Brian Matthews in Acta Cryst. vol 20, to see how seriously anomalous scattering was already taken as a source of phase information in macromolecular crystallography in the 1960's. In spite of that, of course, there would always be the unhappy cases where the anomalous differences were too noisy, or the data processing program too unsophisticated to filter them adequately, so that only the isomorphous differences would be useful. It was in order to carry out such filtering that Brian Matthews made another crucial contribution in the form of the Local Scaling method (Acta Cryst. A31, 480-487). With best wishes, Gerard. -- On Wed, Jun 06, 2012 at 11:02:05AM -0400, Dyda wrote: I suspect that pure MIR (without anomalous) was always a fiction. I doubt that anyone has ever used it. Heavy atoms always give an anomalous signal Phil I suspect that there was a time when the anomalous signal in data sets was fictional. Before the invent of flash freezing, systematic errors due to decay and the need of scaling together many derivative data sets collected on multiple crystals could render weak anomalous signal useless. Therefore MIR was needed. Also, current hardware/software produces much better reduced data, so weak signals can become useful. Fred [32m******************************************************************************* Fred Dyda, Ph.D. Phone:301-402-4496 Laboratory of Molecular Biology Fax: 301-496-0201 DHHS/NIH/NIDDK e-mail:fred.d...@nih.gov Bldg. 5. Room 303 Bethesda, MD 20892-0560 URGENT message e-mail: 2022476...@mms.att.net<mailto:2022476...@mms.att.net> Google maps coords: 39.000597, -77.102102 http://www2.niddk.nih.gov/NIDDKLabs/IntramuralFaculty/DydaFred *******************************************************************************[m -- =============================================================== * * * Gerard Bricogne g...@globalphasing.com<mailto:g...@globalphasing.com> * * * * Global Phasing Ltd. * * Sheraton House, Castle Park Tel: +44-(0)1223-353033 * * Cambridge CB3 0AX, UK Fax: +44-(0)1223-366889 * * * ===============================================================
