Well - I would start with a self rotation analysis. That non-cryst twofold and three folds would suggest something with 3-2 symmetry. I vaguely remember an insulin structure with the hexamer 3-fold in similar orientation..
And this paterson peak "one major off origin peak at 0.5 0.5 0.173" might help. What about trying to reindex to halve the A B axes, (reindex h/2,k/2,l will work and wont change the spacegroup.) You say 22 molecules but I would guess there is really 24, so reduce the volume to a quarter and you want 6 .. Check the self rotation for the smaller cell and see if there are still 3 folds and 2 folds, then solve it in the reduced cell and extend the model later Is that as clear as mud?? Eleanor On Sat, 23 Jan 2021 at 11:45, Andrew Lovering <a.lover...@bham.ac.uk> wrote: > Dear All, > > > Having some fun with a marginal SAD S phasing case that you may be able to > help me on. > > My primary question is "does strong tNCS artefactually inflate FOM > scores"? I have a solution with FOM 0.48 to 3.5Ang or so and the map isn't > as good as I'd expect (in either hand). > > > -more detail if this helps: > > We have collected 3 sweeps at 1.77A wavelength, Rpim is good 2% or less, > xtriage Z-score is 2, aimless suggests anom signal to 3.9A, as does shelxc, > no signs of radiation damage, anom multiplicity is 40, cc anom 0.4 overall > > > Cell is P41212/P43212, 146.9 146.9 335.1 diffracts to 2Ang or so which > suggests 50% solvent = 22 copies in asu! > > > each copy should have 2 disulphides and 6 extra S in Met. I am using dsul > keyword in shelxd. I ask for a variety of sites, usually gets 240+, there > is also 300mM Mg and 20mM As in conditions (site completion in phaser with > Mg or As doesnt really help) > > > When we look at native patterson we see one major off origin peak at 0.5 > 0.5 0.173 fractional, 25% height of origin > > -and a smaller peak at 0.35 0.35 0.5 10% of origin > > > I have tried everything. Changing phasing limits, programme, cutting back > data range, number of sites. But I can get a decent sites pdb from > shelx/crank2 which popped into phenix autosol gives stats that wrongly make > me think I am close (fom 0.4-0.5, score 30+, skew 0.1+). My model has no > molrep possibilities and likely no alpha helical content > > > If I run the substructure sites through profess, I get two nice operators: > > -(op1) polar 90 -44 179.9 trans -72 -73 -444.6 rotation order 8, N atoms > paired 74 from 16 of input atoms > > -(op2) polar 90 -87 180 trans -147 -9 -863 rotation order 2 paired 8 atoms > from 8 of input > > (profess notes these two sit 43 degrees apart) > > > I can see that op1 has a translational component that is my tNCS vector > (-0.5 -0.5 and 0.17 away from 0.5)....and that likely I have 4 fold > operator that sits over my crystallographic 2-fold, which is 45 degree from > another 2 fold (self rotation function attached..). I would welcome a > better description of this 😊 > > Using these operators (or indeed a pure tNCS only operator) in dm gives > good correlation but again no map improvement. Is it worth playing with > nmol? > > > Any suggestions welcome, before we hit this with some higher electron > derivatives! > > > Thanks > > Andy > > > > > > > ------------------------------ > *From:* > > *Sent:* January 23, 2021 11:08 AM > *To:* Andrew Lovering (Biosciences) > *Subject:* Srf > > > ------------------------------ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 > ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
