Representative Kunitz-type toxins are LmKTT-1a from scorpion, Conkunitzin-S1 (PDB Code: 1Y62) from conus, APEKTx1 (PDB Code: 1WQK) from sea anemone, α-DTX (PDB Code: 1DTX) from snake, and HWTXI-XI (PDB Code: 2JOT) from spider. The known disulfide bridges are labeled in black lines. The red dotted line suggests a possible new disulfide bridge.