Dear All, I suspect the way out of this is a new crystal (!) but interested to hear any advice.
I have two crystal forms of a 500aa protein, vaguely tube-shaped 1=P3121, diffracts to 4.1 ang, 3 copies in asu, 86% solvent; map indicates it is a relative of other folds (but those are not so close that they'd be a good guide to sequence register). I have selenomet SAD phases which helps identify Met positions. The 3-fold and high solvent give a great map but you wouldn't want to build it and buccanner and phenix think similar 2=I222, 2 copies per asu, 66% solvent. This has a cell that gives wildly anisotropic diffraction - ~3, 3.5, 4.3 down different axes. Not really rectified by staraniso. No phases So I can cut the density out of form 1 map (using secondary structure elements of a rough PDB as a mask), and use phaser with this density as search model to find the two copies with a TFZ of about 10. The phaser map shows a bit of detail and the solution has placed the protomers such that they agree with a self-rotation function. Phenix find_ncs on phaser map similarly agrees (as I would expect). Now...I have an eye on multi-crystal averaging between the two forms. BUT the phaser map isn't good enough to manually place the PDB used in cut-out density, and I can't see a straightforward way of using the angle info in phaser sol to perform a co-ordinate transformation (but I think ccp4bb users will put me right on this - I'd imagine placing the PDB into the cutout density mtz then using PDBset?). I tried converting the phaser mtz to a map using FFT then using phased TF in Molrep to place the PDB but this didn't work, complaining about the grid used. One last caveat - I have multiple sets for the I222 that intriguingly differ by 12 angstrom down a 240 ang axis: doing multi-crystal averaging between these two forms achieves little when I would expect otherwise (all the NCS correlations are good, high initial agreement) Like I said...fingers crossed for a new crystal form! Andy ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
