Hi Gerard and Bernhard, As a postdoc in an unnamed small molecule lab, I was instructed by my lab head to get better unit cell estimates prior to data collection owing to error propagation from the uncertainty on cell dimensions through to the esd on atomic bond lengths and angles when refining in shelxl. To verify this (what, you believed everything your postdoc advisor told you?), I took a working dataset and increased (only) the error on unit cell dimensions in the instruction file for the final round of full matrix least squares refinement in shelxl. Sure enough, the errors on the bonds and angles shot up. I was more careful in determining the unit cell thereafter. That is, until, I became a macromolecular crystallographer...
After an inciteful (sp? lol) discussion with Wladek about cell dimensions, I was directed to read this paper: Acta Crystallogr D Biol Crystallogr. 2015 Nov 1; 71(Pt 11): 2217–2226. Have a look, it is interesting. Having never followed up on these studies to see what happened to bonds and angles in proteins and their ligands when varying cell dimensions, I can't say with any confidence. However, I would guess that the quality of the refined ligand coordinates could only be as good as some combination of factors including but not limited to 1) the data (resolution, B factor, etc), 2) the actual occupancy of the ligand, and 3) the restraints employed. jbb Jeffrey B. Bonanno, Ph.D. Department of Biochemistry Albert Einstein College of Medicine 1300 Morris Park Avenue Bronx, NY 10461 off. 718-430-2452 fax. 718-430-8565 email jeffrey.bona...@einsteinmed.org -----Original Message----- From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Gerard DVD Kleywegt Sent: Wednesday, July 15, 2020 11:49 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Quote source inquiry Well, I've had this in my CSHL X-ray Course talk for many years. In the attached 2007 Acta D paper it says (p 95): "Macromolecular X-ray crystallography is a notoriously poor method for determining the structure of small molecules that are bound to macromolecules [...]" and then goes on to explain why this is the case. In the attached 2003 paper (pooling the wisdom of several of the usual suspects, including Eleanor) it says something similar (p 1057): "Coordinates of molecules that have been determined in complex with macromolecules previously can of course also be retrieved from the PDB (Bernstein et al., 1977; Berman et al., 2000), HIC-Up (Kleywegt and Jones, 1998), or CHEMPDB (Boutselakis et al., 2003). However, one should keep in mind that these coordinates are the result of refinement against comparatively low-resolu- tion data where the small molecule constituted only a minute fraction of the total scattering matter. This makes these coordinates inherently much less accurate than those obtained from the CSD. In addition, the coordi- nates may contain errors due to the use of incorrect restraints. Hence, such coordinate sets should only be used as a last resort, and only after verification that they are reliable. The latter can be facilitated by inspection of the electron density for the compound in question, for instance at the Uppsala Electron-Density Server (http:// fsrv1.bmc.uu.se/eds) (G.J.K. et al., submitted)." Happy to be confused with George though! --Gerard (no, the other one) On Tue, 14 Jul 2020, Bernhard Rupp wrote: > Hi Fellows, > > > > afaicrimps (as far as I can recall in my progressing senility) > someone once wrote/stated/cursed somewhere that "Macromolecular > refinement is not a small molecule structure determination method". > > > > Any citable source - George Sheldrick might be a suspect. > > > > Thanks & best regards, BR > > > > ------------------------------------------------------ > > Bernhard Rupp > > <https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww. > hofkristallamt.org%2F&data=02%7C01%7Cjeffrey.bonanno%40einsteinmed > .org%7Cf0b1878c0df040bb2e5308d828d6b0ed%7C9c01f0fd65e040c089a82dfd51e6 > 2025%7C0%7C0%7C637304250594203532&sdata=9FFCpYd9D%2BrHR48DtL%2BglM > W2dbZ%2FmSTw0fF88XRwR7o%3D&reserved=0> > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.h > ofkristallamt.org%2F&data=02%7C01%7Cjeffrey.bonanno%40einsteinmed. > org%7Cf0b1878c0df040bb2e5308d828d6b0ed%7C9c01f0fd65e040c089a82dfd51e62 > 025%7C0%7C0%7C637304250594203532&sdata=9FFCpYd9D%2BrHR48DtL%2BglMW > 2dbZ%2FmSTw0fF88XRwR7o%3D&reserved=0 > > <mailto:b...@hofkristallamt.org> b...@hofkristallamt.org > > +1 925 209 7429 > > +43 676 571 0536 > > ------------------------------------------------------ > > Many plausible ideas vanish > > at the presence of thought > > ------------------------------------------------------ > > > > > ###################################################################### > ## > > To unsubscribe from the CCP4BB list, click the following link: > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww. > jiscmail.ac.uk%2Fcgi-bin%2FWA-JISC.exe%3FSUBED1%3DCCP4BB%26A%3D1&d > ata=02%7C01%7Cjeffrey.bonanno%40einsteinmed.org%7Cf0b1878c0df040bb2e53 > 08d828d6b0ed%7C9c01f0fd65e040c089a82dfd51e62025%7C0%7C0%7C637304250594 > 203532&sdata=MdVq312BDC5B6EjIyAEaGjDXt%2B9SsSjIaw%2FH9Nxfemg%3D&am > p;reserved=0 > > This message was issued to members of > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.j > iscmail.ac.uk%2FCCP4BB&data=02%7C01%7Cjeffrey.bonanno%40einsteinme > d.org%7Cf0b1878c0df040bb2e5308d828d6b0ed%7C9c01f0fd65e040c089a82dfd51e > 62025%7C0%7C0%7C637304250594203532&sdata=25UsGO%2FeC2aTI9f0puoG5nh > SUKhyCoMeVRKgQdncy7k%3D&reserved=0, a mailing list hosted by > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.j > iscmail.ac.uk%2F&data=02%7C01%7Cjeffrey.bonanno%40einsteinmed.org% > 7Cf0b1878c0df040bb2e5308d828d6b0ed%7C9c01f0fd65e040c089a82dfd51e62025% > 7C0%7C0%7C637304250594203532&sdata=ATQYFzhj6lreD1vETky3HaN2N8opg5x > 3szRPRRZ6fwc%3D&reserved=0, terms & conditions are available at > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww. > jiscmail.ac.uk%2Fpolicyandsecurity%2F&data=02%7C01%7Cjeffrey.bonan > no%40einsteinmed.org%7Cf0b1878c0df040bb2e5308d828d6b0ed%7C9c01f0fd65e0 > 40c089a82dfd51e62025%7C0%7C0%7C637304250594203532&sdata=NmdJIawDMh > tarwNE8w4ssEYxAGzp0drlc3mNXwTdbgo%3D&reserved=0 > Best wishes, --Gerard ****************************************************************** Gerard J. 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