The modified aflatoxin ligand at segment 303 in puzzles 1440 and 1445. The ligand is already bonded to three locked segments of the protein. The "show bonds (non-protein)" and "show bondable atoms" view options highlight the bondable atoms in the ligand. All the bondable atoms are oxygen.
The type of hydrogen bond each oxygen can accept depends on how the atom is already bound.
Ligand atoms 2 and 6 can act as hydrogen bond acceptors. Ligand atoms 12, 16, 22, 23, and 25 can act as either hydrogen bond acceptors or hydrogen bond donors.