The command mlp calculates molecular lipophilicity potential (MLP) maps for proteins. Nonprotein atoms are ignored. By default, the results are shown with coloring on the molecular surface ranging from dark cyan (most hydrophilic) to white to dark goldenrod (most lipophilic).
The calculation is based on pyMLP:
Molecular structures: Perception, autocorrelation descriptor and SAR studies. System of atomic contributions for the calculation of the n-octanol/water partition coefficients. Broto P, Moreau G, Vandycke C. Eur J Med Chem. 1984;19(1):71-78.
MLPP: A program for the calculation of molecular lipophilicity potential in proteins. Laguerre M, Saux M, Dubost JP, Carpy A. Pharm. Sci. 1997;3(5-6):217-22.
Optimizations for speed, including a distance cutoff, have been added in ChimeraX. See also: color, surface, volume, measurements, the ChimeraX MLP highlight, some comparisons at the Chimera website
The pyMLP program includes values for nonhydrogen atoms in the 20 standard amino acids plus HYP (hydroxyproline) and PCA (pyroglutamic acid). Other atoms are ignored. The potential at each grid point is a sum over the atomic contributions. Positive potentials correspond to more lipophilic (more hydrophobic) areas, negative to less lipophilic (more hydrophilic) areas.
The method specifies how the atomic values propagate through space, with factors based on the distance d from the atom (default fauchere):
The spacing s of the map grid can be specified in the range 0.1–10.0 Å (default 1.0). Decreasing the spacing increases map size and calculation time.
With color true (default), molecular surfaces for the protein chains containing the specified atoms are generated if they do not already exist and colored by the MLP, and the surface patches for those atoms displayed. A separate MLP map is computed for each surface (protein chain), and its value ranges reported in the Log. Defaults for the coloring palette-options are
palette lipophilicity range -20,20
Different choices of method and/or maxDistance can give very different values, and the range may need to be adjusted.
With color false, a single MLP map will be calculated based on the specified atoms (disregarding any nonprotein atoms), and no surface calculations or coloring will be performed. This is only useful in combination with map true.
With map true (default false), MLP maps will be opened as volume models. This allows subsequently recoloring surfaces by the map values (without having to recalculate them on the fly) using color, and/or saving the maps to file.