GETAX (CCP4: Supported Program)
NAMEGETAX - real space correlation search
PURPOSEReal space searching for rotation axis of a D<n> or C<n> multimer ( <n> = 2,3,4,5,6,... ).
If you have: you can start using this program to find the translational part of your NCS operators.
It has worked in several cases with even very poor phases ( 20 molecules/au, <fom>=0.25 to about 6Å resolution).
VERSIONVersion 2.5 (14. April 1998)
SYNOPSISgetax MAPIN foo.map [ XYZIN foo1.pdb ] [ XYZOUT foo2.pdb ] [ MAPOUT bar.map ]
POLARRFN) and a crude knowledge of the size/shape of your molecule(s).
MAPINmap covering a whole unit cell with axis order X=fast, Y=medium, Z=slow changing index.
This map can be a 6 Angstroem MIR map on a 2 Angstroem grid. So if you use fft you don't have to worry about getting the grid right, since fft takes 1/3rd of the high resolution anyway. Sometimes it can be helpful to try finer grid spacings (this slows down the calculation, though).
Depending on your spacegroup, you will have to change the extent and/or axis order with MAPMASK.
XYZINa PDB file with an initial model for the correlation search.
see: INPUT XYZ
This can be a PDB file with orthogonal coordinates either before (OUTPUT XYZ) or after initial interpolation (OUTPUT GXYZ).
To be sure that everything works fine: have a look at this output file with your favourite graphics program (O or RASMOL or whatever ...): there should be no overlap between the segments and the rotation axis should be properly oriented.
MAPOUTis an output map with correlation coefficients at each grid point. There are two possible correlation coefficients:
Available keywords are:
POLAR <omega> <phi> <kappa> [<omega-2> <phi-2> [<kappa-2>] ]Polar angles of a selfrotation solution (definition as in POLARRFN).
Combining two selfrotation solutions:
If you have a twofold perpendicular to your rotation axis (e.g. D4 symmetry) you can give the polar angles as <omega-2> and <phi-2> (<kappa-2> defaults to 180.0). A corresponding sphere/disk will be built. The program stops if the two rotations aren't perpendicular. If they are perpendicular within an error of 5 degrees, the program calclulates a new 2-fold which now is exactly perpendicular, thus correcting possible rounding errors of e.g. POLARRFN.
ncode = orthogonalization code:
Builds a sphere with radius <outer-radius>. You can omit a smaller inner sphere by giving <inner-radius>.
The sphere will be divided into <ifold> segments (where <ifold> is determined by <kappa>) and rotated so that its rotation axis is parallel with the selfrotation axis and its center is at (0 0 0). You can write this sphere out to logical XYZOUT.
To get a rough idea what your protein looks like: use the molecular weight Mr to get radius of assumed spherical protein:
1.23 * Mr * 0.75 radius = ( ---------------- ) ^ 0.333 pidefault: <outer-radius>=25. <inner-radius>=0.
Builds a disk with outer radius <outer-radius> and height <height>. You can omit a smaller inner circle by giving <inner-radius>.
The disk will be divided into <ifold> segments (where <ifold> is determined by <kappa>) and rotated so that its rotation axis is parallel with the selfrotation axis and its center is at (0 0 0). You can write this disk out to logical XYZOUT.
default: <outer-radius>=25. <height>=15. <inner-radius>=0.
AX2 and AX3 don't make any difference in the result (but AX3 keeps the absolute values of the output correlation map at a reasonable height).
defaults: CORR NOPACK AX4
Takes only every <iskip>th point of each segment in your sphere/disk to compute correlation coefficients. This is a good idea if your sphere/disk is rather big. It can save a lot of CPU. But take care that you keep at least ~500 points in each segment.
If keyword AUTO is present, the actual value of iskip is set so that aproximately <askip> points per segment are used.
default: AUTO 500
Unless you have calculated your map on a very fine grid, it does make things worse. And perhaps you'll miss the right solution !! It doesn't save a lot of CPU, since we have to interpolate the values at the end anyway.
The default is also a very reasonable value.
Unless you know already where to look for your multimer, I would always search the whole unit cell.
default: whole unit cell
If you have a pretty good idea what your molecule looks like and how it is oriented (but not positioned) this could be quite helpful. But some restrictions:
At the end of the search the found correlations are sorted according to height and the <top> number is reported.
default: <report>=1. <top>=20
SEE ALSOfft(1), mapmask(1), peakmax(1), dm(1), ncsmask(1).
Clemens Vonrhein <firstname.lastname@example.org> Last modified: Tue Apr 14 18:42:11 CEST 1998