NCSMASK (CCP4: Supported Program)

NAME

ncsmask - averaging mask manipulation program

SYNOPSIS

ncsmask [ MSKIN foo.msk / XYZIN foo.pdb ] MSKOUT bar.msk
[Keyworded input]

DESCRIPTION

This program performs operations on non-crystallographic symmetry masks. It is ideal as a precursor to `dm', since it contains a more sophisticated treatment of mask overlap, and may avoid some problems commonly caused by poorly defined masks.

Input can be from a PDB file, in which case a mask is generated from spheres around all atoms. A crude 'sphere mask' can be constructed by making a PDB file with only a few atoms and specifying a large radius.

Alternatively input can be from a CCP4 format map/mask file.

The mask may then be modified by expanding or contracting, smoothing the boundary, reducing from a multimer to a monomer (in some cases), removing crystallographic- or non-crystallographic symmetry overlap and altering the mask box size.

This program should not normally be used for generating solvent masks, since it does not impose crystallographic symmetry or unit cell repeat. See mapmask for further details. However, these masks can be used in DM 1.7.1 or later.

INPUT/OUTPUT FILES

XYZIN
is the input PDB file
MSKIN
is the input mask file
MSKOUT
is the output mask file

KEYWORDED INPUT

The GRID and SYMMETRY cards are useful if input is from a .pdb file, otherwise the information is taken from the input mask header. Available keywords are:
AVERAGE, AXIS, EXPAND, GRID, MONOMER, NOTRIM, OVERLAP, PEAK, RADIUS, SMOOTH, SYMMETRY, XYZLIM

GRID <nx> <ny> <nz> | SPACING <x> [ <y> <z> ]

Set the sampling grid over the unit cell to <nx>*<ny>*<nz>. The default is 1.0 Angstrom spacing.
Alternatively, the SPACING subkeyword allows you to set the grid spacing; if only x is specified then this gives x Angstrom spacing along all axes, otherwise x, y and z are the spacings along each axis.

The GRID keyword is ignored if a mask is input.

SYMMETRY <spacegroup name/number>

Set the spacegroup symmetry for the mask. The default is taken from the input mask if a mask is input, or P1 if a .pdb file is input.

AXIS <x> <y> <z>

Change the default output axis order. The first axis specified will vary fastest.

XYZLIM <x1> <x2> <y1> <y2> <z1> <z2>

Changes the default mask extent. <x1>-<z2> are either in grid units or fractional coordinates. If the new extent is smaller than the input mask extent, the input will be truncated, if the new extent is larger the mask will be padded with zeros. The default is either the extent of the input mask or the extent of the input .pdb file + sphere radius + 3.0 Angstrom. See however the NOTRIM card.

RADIUS <rad>

Set the sphere radius for building a mask out of atoms. Default=3.0 Angstrom. A much larger value could be used to build a mask around C-alpha or sulphur coordinates, for example.

PEAK <num>

Pick the <num> largest connected regions of the mask, and delete all others. `PEAK 1' is particularly useful for tidying up a correlation mask (see maprot).

EXPAND <rad>

Expand/contract the mask. This function expands the mask by <rad> Angstrom in all directions. The mask will not be expanded beyond the current mask extent, if this is required the XYZLIM card should be used to increase the mask extent. A negative value will contract the mask.

SMOOTH <rad>

Smooth the mask using a sphere of radius <rad>. This will eliminate features smaller than <rad> from the surface of the mask. Maximum radius ~5 grid points.

AVERAGE <nncs>

Enter NC-symmetry elements for overlap removal. (Note that this card has the same format as the `dm' `AVERAGE' card). This card is followed by <nncs> rotation/translation matrices on subsequent lines in either CCP4 or O/RAVE format.
CCP4 Formats (see also lsqkab):
ROTATE EULER <alpha> <beta> <gamma>     (Euler angles)
TRANSLATE <t1> <t2> <t3>
or
ROTATE POLAR <omega> <phi> <kappa>      (Polar angles)
TRANSLATE <t1> <t2> <t3>
or
ROTATE MATRIX <r11> <r12> <r13> <r21> <r22> <r23> <r31> <r32> <r33>
TRANSLATE <t1> <t2> <t3>
O/RAVE Format

OMAT
<r11> <r21> <r31>
<r12> <r22> <r32>
<r13> <r23> <r33>
<t1> <t2> <t3>
where
x' = <r11>x + <r12>y + <r13>z + <t1>
y' = <r21>x + <r22>y + <r23>z + <t2>
z' = <r31>x + <r32>y + <r33>z + <t3>
(note that the rotation matrix is transposed with respect to CCP4 matrix format.)

These are the operations which map the density in the region covered by the input mask onto the other equivalent regions. The first operator must be the identity matrix. The mask is input in CCP4 mask format on the input file label MSKIN, and should cover just one monomer or averaging domain, NOT the whole unit cell.

MONOMER

Reduce a multimer mask to cover only a monomer. This option will generate a mask covering an arbitrarily chosen monomer from a multimer in the case where the NCS consists ONLY of a SINGLE PROPER ROTATION AXIS of any order. An arbitrary segment covering an angle of 2*pi/<nncs> is selected and the rest of the mask is removed.

OVERLAP [ <ncycle> ]

Perform overlap removal. Overlap removal will be performed by removing pixels from the surface of the mask. The mask is overlapped with its crystallographic- and non-crystallographic symmetry related partners (see SYMMETRY and AVER cards). The overlap removal calculation may not remove all overlap on the first cycle, if <ncycle> is specified, overlap removal will be repeated this number of times.

NOTRIM

Disable mask trimming. The default is to reduce the mask extent to obtain the minimum box which will contain the final output mask. With NOTRIM, the mask extent will be the same as the input mask or the values on the XYZLIM card if it is present.

NOTES

The calculations are performed in the following order:
  1. Mask input/generation
  2. Peak picking
  3. Expansion/Contraction
  4. Smoothing
  5. Monomer generation
  6. Overlap removal
  7. Extent trimming

If you want to do them in a different order, run the program several times.

Read your output. When removing overlap, check that the input and output masks fill a sensible volume of the unit cell. Don't complain until you have done this.

EXAMPLES

To remove the overlap from a mask for input to `dm': 
#
ncsmask mskin ins.msk mskout ins1.msk << eof
AVERAGE 2
OMAT
 1.000  0.000  0.000
 0.000  1.000  0.000
 0.000  0.000  1.000
 0.000  0.000  0.000
OMAT
 -0.88284    -0.46960    -0.00849
 -0.46899     0.88238    -0.03808
  0.02537    -0.02964    -0.99924
 82.80000     0.10000   -34.10000
OVERLAP
END
eof

To make a mask from pdb file and remove overlap (note that `dm' doesn't care about the grid on which input masks are calculated): 

#
ncsmask xyzin ins.pdb mskout ins1.msk << eof
SYMMETRY R3
RADIUS 3.0
AVERAGE 2
ROTATE EULER 0.0 0.0 0.0
TRANSLATE 0.0 0.0 0.0
ROTATE EULER -29.6  180.0    0.0
TRANSLATE 0.3  0.1 -0.1
OVERLAP
END
eof

SEE ALSO

dm, lsqkab, mapmask, maprot, bones2pdb.