Alignment of the Protobothrops flavoviridis three-finger toxin [AB851958] with selected sequences from colubrid, elapid, and viperid venoms. Not surprisingly, the Protobothrops sequence aligns most closely with that from Sistrurus, one of only two other crotalid 3FTx sequences available to date. Both the Protobothrops and Sistrurus sequences share an N-terminal sequence, EPGYT; however, the first two Cys residues in the Sistrurus sequence occur in positions 8 and 11, whereas the Protobothrops sequence has paired Cys residues at positions 8 and 9. The Protobothrops sequence also has a Pro residue in position 12 which does not occur in the Sistrurus mRNA. Based upon the mapping of disulfide bonds in candoxin, the elapid 3FTx most similar to the crotalid toxins , it appears that in the Sistrurus toxin Cys-11 is bonded to Cys-18, whereas in the Protobothrops toxin, Cys-9 is bonded to Cys-18 (red arrow), but these tentative assignments require experimental confirmation. All other disulfide bonds are indicated with black arrows.