Residue varinats default to the pH 7 forms, specifically protonated LYS, ARG, HIS, and N-terminus
and deprotonated ASP, GLU, CYS, and C-terminus. 'deprotonated' CYS is generally assumed to be the
disulfide form. Where given teh RCSB variant code is used. Ther is no decision on what to use where
these codes are not defined.