HB plots of the open and closed forms of beta-lactoglobulin are very similar, all unique motifs can be recognized in both forms. Difference in HB plots of open and ligand-bound form show few important individual changes in tertiary hydrogen bonding pattern. Especially, the formation of hydrogen bonds between Y20-E157 and S21-H161 in closed form might be crucial in conformational rearrangement. These hydrogen bonds lie at the bottom of the cavity, which suggests that the closure of the entrance of a lipocalin starts when a ligand reached the bottom of the cavity and broke hydrogen bonds R123-Y99, R123-T18, and V41-Q120. Lipocalins are known to have very low sequence similarity with high structural similarity. The only conserved regions are exactly the region around 20 and 160 with an unknown role.