Figure 8
From: Fast automated placement of polar hydrogen atoms in protein-ligand complexes

Example of a hydrogen bond network. Hydrogen bond network in the active site of PDB structure 1ps3 as perceived by Protoss. O2, O3 and O4 are hydroxyl atoms in the ligand. The gray nodes are the nodes that are removed by the cycle decomposition algorithm. The node with the star is the root of the tree traversal.