Absence of phospholipase A2 in most Crotalus horridus venom due to translation blockage: comparison with Crotalus horridus atricaudatus venom

To investigate the peculiar absence of phospholipases A2 (PLA2s) in most Crotalus horridus (CH) venom, we cloned and sequenced the venom PLA2s of three CH specimens from different regions. The results revealed that all the venom glands contained mRNAs that encoded an acidic PLA2 (designated as either CH-E6 or CH-E6’). The predicted CH-E6 from the Iowan CH and CH-E6’ from the South Carolinian CH differed by only one amino acid residue, while the PLA2 cDNA cloned from the Kentuckian CH contained an early stop codon instead of a Tyr22 codon. Only the individual South Carolinian CH venom was found to contain the CH-E6’ protein whose mass was confirmed by MALDI-TOF analysis. Our results suggest that low PLA2 expression levels in most CH venom can be attributed to translation blockage. We also purified two acidic PLA2s and canebrake toxin from the pooled venom of Crotalus horridus atricaudatus (neurotoxic CH subspecies). One of the acidic PLA2s was identical to CH-E6 and showed high lipolytic activity and weak anti-platelet activities. The possibility that C. h. atricaudatus could be a hybrid between CH and Crotalus scutulatus is discussed.