Editing Modeling and Editing Structures (section)

==Protonating ligands==
If your ligands come in with valid valencies and formal charges, PyMOL's h_add command can protonate ligands. (NOTE that there is a minor technical hiccup with SD-files which are loaded by default as immutable "discrete" objects.) Suffice it to say that in order to make changes to the chemical structure, an object must be loaded with the "discrete" flag set to zero.
Unfortunately, much of the molecular editing stuff remains to be documented. Here's an example sequence, but I'm not sure it will help to much...as indicated in the manual, this is immature functionality with some major gaps. Attach in particular is very limited...

<source lang="python">
# show valences
set valence=0.05

# load cysteine fragment
fragment cys

# remove hydrogens
remove (hydro)

# edit gamma S
edit cys////sg

# add hydrogen
attach H,1,1

# add planer, trivalent nitrogen onto C terminus
edit cys////C
attach N,3,3

# edit that nitrogen
edit (elem N and neighbor cys////C)

# attach a tetrahedral methyl (note random position)
attach C,4,4

# here's an example of adding a whole residue from the library
edit cys////N
editor.attach_amino_acid("pk1","ace")

# now restore missing hydrogens (note that the names are off...)
h_add
</source>