The electrostatics menu (ELECTR)

Introduction.

This menu is for manipulating electrostatic maps. The present menu contains two options for reading maps from DelPhi/InsightII.

Note - Positioning of molecules relative to map:

Maps and molecules will be positioned correctly if the coordinate space that was used to calculate the map is left unchanged in the molecule coordinate file.

Read a formatted DelPhi map (GETFDM)

This option gets a formatted DelPhi map saved from Insight II. Formatted grids can be generated from inside InsightII by checking the ASCII button in the 'PUT GRID' option.

This option should be used carefully as maps will be positioned correctly only if the 'Origin on grid point' option has been turned on upon calculating the electrostatic map with DelPhi. (The 'Origin on grid point' option can be found in the 'GRID' option in the 'SETUP' menu in DelPhi/InsightII.)

If the 'Origin on grid point' option is left unchecked, then the electrostatic maps will be shifted by a fraction of a grid point in the x and y directions and even more in the z direction.

This results from a bug in Insight II (No. 75400), that simply writes a wrong grid to the ASCII file. This may not have large consequences when inspecting maps derived for large molecules, but nevertheless the error is there and does produce artefacts.

Be aware that reading a formatted map takes a looong time...

After reading the map you can choose to have the extremes removed from the map; i.e. the only values that will be kept are the ones within a specified number of standard deviations from the average value of the potential map.

(See STAELM for information on how the average value is calculated).

Read an unformatted DelPhi map (GETUDM)

This option reads an unformatted Delphi map. Unformatted DelPhi maps can be generated directly with DelPhi or can be written from InsightII. This is the default map type written from both DelPhi and from InsightII.

It should be noted that the file format differs from the one reported in the Insight II Users Guide page 14-5 with respect to the three 4-byte floating point entries that are described as being the grid dimensions (x, y, z). This is not the case! The error (No. 79062) is, however, correctable as these incorrect grid dimensions have been used to calculate the fractional starting and ending points of the grid.

  (Fractional starting pos. X) = (Absolute starting pos. X)/(Grid extent X)
The correct starting and ending postions can thus be retrieved by applying the inverse of the above equation. These values can in turn be used to calculate the correct grid extent.

After reading the map you can choose to have the extremes removed from the map; i.e. the only values that will be kept are the ones within a specified number of standard deviations from the average value of the potential map.

(See STAELM for information on how the average value is calculated).

Read an unformatted UHBD/GRID map (GETUUM)

This option reads an unformatted UHBD potential map written in the GRID format. This option can thus also be used for reading an original GRID map.

After reading the map you can choose to have the extremes removed from the map; i.e. the only values that will be kept are the ones within a specified number of standard deviations from the average value of the potential map.

(See STAELM for information on how the average value is calculated).

Calculate statistics for the default electrostatic map (STAELM)

This option calculates the parameters: Average, Average deviation, Standard deviation, Skewness and Curtosis.

These parameters are calculated twice: first taking all values into account, and secondly taking only ABS(values) greater than 0.0001 into account. (The latter is used for removing extremes after reading a map, GETFDM, GETUDM and GETUUM).

This is done because the large number of grid points bearing a value very close to, or identical to zero for many purposes are better left ignored.

Scale the default map AVG and SDEV (SCAELM)

This option scales one map onto another. The scaling is done such that the average value and the standard deviation of the two maps become identical.

Calculate first derivative of the default map (GRDELM)

This option calculates the first derivative of the default map with respect to distance.

(Still experimental)

Negate the default map. (NEGELM)

This option negates the default map; i.e. every value is multiplied by -1.

Make histogram of an electrostatic map (HISELM)

This option makes a histogram of the values present i a selected map. The user is prompted for the map number, the resolution of the histogram and the value of truncation for the histogram.

Run DelPhi (RUNDEL)

This option runs DelPhi but is still very incomplete.

DelPhi needs to be installed.

Get own DelPhi map (GETODM)

This options gets the DelPhi map produced by RUNDEL.

Solve Poissons equation (POISOL)

Experimental Poisson solver for a small uniform grid.

Solve Coulombs law (COUSOL)

Simple calculation of the electrostatic potential in a small uniform grid.

Remove convex points but keep almost concave ones (OUTELM)

The OUTELM option will loop over all points in the map N times. You will be prompted for N; the default is 10.

A convex point in this routine is defined as a point having three or more neighbours being more than X% of the map span lower than the value itself, and not having three or more neighbours that have a value X% higher. - X is given by the user Points with a value in the top 5% of the map span is always kept This routine treats all numbers in an 'ABS' way - only 'ABS' statements are used to calculate whether the value falls within the above criteria.

All points deemed convex are next assigned the value of the average of the three or more points that "made" the original point convex.

This option only works well on all maps.

Trucate map between user limits (TRUELM)

This option trucates the default map between limits given by the user.

This option works well on all maps, but you may find that it is not possible to trucate the map between the desired limits because of a too low WHAT IF internal resolution of the map. In that case you should try to increase the resolution when reading the map by keeping a lower number of standard deviations.

Flaten map (FLAELM)

This option put all values above a certain limit at that limit.

Smoothen map (SMOELM)

The SMOELM option will cause WHAT IF to prompt you for the number of cycles. Thereafter so often as asked every point in the map will be replaced by two times its own value plus the value of its six orthogonal neighbours divided by eigth. The edges of the map remain unaltered.

Compare SMOOTH in the MASMAP menu.

Remove convex points (CONELM)

Convex points are gridpoints that form a sharp external protrusion in the map. They have more empty than filled points around them. In practice they are defined as points in the shell with three or more orthogonal neighbours that have the value zero.

The option CONVEX will loop over all points, and sets all points with a value between 1 and 99 to zero when they border at least 3 other zero points. The option got its name because it removes the points that are at a convex surface. See also the OUTER option.

This option only works well on WHAT IF generated maps, or maps scaled such that the values fall in the 0 till 100 range. Other maps will cause this option to produce strange error messages.

This will be corrected ......

Remove one layer from the shell (PEEELM)

The PEEELM option allows you to remove the outside layer of density created by the SRFMAP option in the MAP menu. You can think of this option as peeling one layer from the shell. If one were to repeatedly peel layers of the shell, one would also remove the wall of tunnels into the protein; and indeed this is what the PEEL option does. However, by stopping the peeling process at the moment that the number of zero's added per cycle becomes smaller than for example 200 or so, one can maintain the tunnels into the protein as part of the shell.

This option only works well on WHAT IF generated maps, or maps scaled such that the values fall in the 0 till 100 range. Other maps will cause this option to produce strange error messages.

This will be corrected......

Remove island and almost-islands (KISELM)

The option KILISL goes over the whole map and removes all non-zero values that have at most one non-zero neighbour point. This way you can remove small islands in the density map, while at the same time cutting the very sharp spikes of larger islands. (Also points at value 100 will be removed by this option!).

This option only works well on WHAT IF generated maps, or maps scaled such that the values fall in the -115 till 115 (but preferably between 0 and 100!) range. Other maps will cause this option to produce strange error messsages.

This will be corrected.

Make average of map zer0. (AVEELM)

This option makes the average of the map zero by adjusting the offset parameter.

Subtract two maps. (DIFELM)

This option checks whether two maps have identical coordinate systems and if so, subtracts the second map from the default map.

Peel the shell of an electrostatic map. (PEELLM)

This option is still to be updated.

And to electrostatic maps (ANDELM)

This subroutine performs a logical AND on two electrostatic maps.

Widen islands (WIDELM)

Still undocumented....

Remove spikes from map (SPIELM)

Still undocumented.....

Find residues near a cavity (ELECAV)

This option writes out a PDB file containing the residues near the largest cavity found in the given molecule.

All residues within the distance wifpar(1080)/100 A are included.