Fred, Two cents - I think the P1 SAXS solution should strongly guide your choice of symmetry constraint above all else in this case: do any of the symmetry-restrained shape reconstructions *improve* the statistics (chi) and stability of the shape (NSD) when compared to the P1 result? Also, it sounds like you have other data - do the theoretical Rs, f/fo, etc of the shapes generated agree well with your other measurements?
Cheers, Kushol Kushol Gupta, Ph.D. Research Associate Van Duyne Laboratory - HHMI/Univ. of Pennsylvania School of Medicine kgu...@mail.med.upenn.edu 215-573-7260 / 267-259-0082 Of course, 222 has not a 4 axis, otherwise it would be a 4-fold axis. But that's the output of the program. P4 exp. model has a 4-fold axis along the longest axis, while the P222 MODEL has a 4-fold axis along the smallest, which doesn't make any sense. Can you imagine something build up with 4 identical subunits and 222 symmtry, but without a 4-fold axis at the molecular level (I mean at the envelop resolution level)? Em 29-07-2010 12:32, Vellieux Frederic escreveu: > Hi, > > To quote you: "even my P222 experimental envelop does have a 4-fold > axis" - this is not suprising, a particle with 222 symmetry does not > have 4-fold symmetry. There are 3 mutually perpendicular 2-fold axes > that intersect at the origin (of the "particle", of the molecule) [and > for the nomenclature, these axes are named the P Q and R axes]. > > Fred. > > Fred wrote: >> Thanks all of you who promptly replied my question. >> I should have been more precise. I was referring to the symmetry of >> the tetrameric particle (point symmetry) at the molecular level not >> at the atomic level. This question has arisen because I have >> collected some SAXS data of my protein in solution and I don't have a >> molecular model to superpose to the experimental envelop. Others >> experimental data, gel filtration and NAT-PAGE, suggest a tetrameric >> particle. On the other side, P1, P2, P222 and P4 experimental >> envelops are quite different. So, I am not sure which symmetry to >> take. Considering the native state (no ligands at all), 4 identical >> subunits and that the interface of oligomarization have to be >> conserved, I would take P222 or P4. However, I can be able to imagine >> such spacial arrangement without a 4-fold axis at the molecular >> level. Indeed, even my P222 experimental envelop does have a 4-fold >> axis. >> I appreciate if you could add some more comments on this. >> Thanks in advance, >> Fred > >
