Questions and problems?

AMBER Histidine residues

Histidine (HIS in normal pdb files) is really one of three possible residues:

HID: Histidine with hydrogen on the delta nitrogen

HIE: Histidine with hydrogen on the epsilon nitrogen

HIP: Histidine with hydrogens on both nitrogens; this is positively charged.

It is up to the user to inspect the environment of each histidine and identify the type that is appropriate.