PROSITE documentation PDOC60020

Janus-faced atracotoxin (J-ACTX) family signature

Janus-faced atracotoxins (J-ACTXs) form a family of insecticidal neurotoxins isolated from the venom of one of the world's most lethal arachnids, the Blue mountains funnel-web spider Hadronyche versuta. J-ACTXs are 36 or 37 residues in length with eight conserved cysteine residues involved in four disulfide bonds, including an extemely rare vicinal disulfide (a disulfide bond between adjacent cysteine residues) that has been shown to be essential for insecticidal activity. J-ACTXs possess two strikingly dissimilar faces. One face presents an almost contiguous charged surface, while the opposing face containing the vicinal disulfide is devoid of ionizable side chains [1].

J-ACTX family proteins have a [C-C-CC-CC-C-C] cysteine arrangement, which is similar to that of the I-superfamily conotoxins (see <PDOC60004>). The three dimensional structure of J-ACTXs possesses a knottin scaffold (see <PDOC60004>) [E1] and III-IV pair of cysteine residues (as marked '#' in schematic representation) involved in a additional disulfide linkage. The cysteine knot motif in J-ACTXs provides high stability and maintains the tertiary structure.

                                    +----------------+
                                 ## |                |
                       CxxxxxxCxxCCxCCxxxxCxxxxxxxxxxC
                       |      |      |    |
                       +------|------+    |
                              +-----------+

'C': conserved cysteine involved in disulfide bond.
'#': Cysteines  three and four are connected to each other through a disulfide
     bond.

Our signature pattern for J-ACTXs contains the eight conserved cysteines involved in disulfide bonds.