Histidine flip prediction in an active site. Histidine flip prediction in structure 1ywr. From left to right: Asp150, His148, Asn155, Leu167. A: Structure as in the PDB. B: Automatically corrected structure. In the top rightern corner is a part of the cocrystallized ligand. The original structure results in one atom clash for His148 and several unsatisfied hydrogen bonding groups. Protoss rotates the histidine to allow for two hydrogen bonds with the backbone atoms of Asp150 and Leu167. Also, Asn155 is flipped to allow for a favorable hydrogen bond with Asp150.