Abstract
Phosphodiesterase (PDE) from snake venom is a glycoprotein which digests extracellular nucleotides to affect the intercellular signaling (Fredholm et al., 2001) and the inhibition of ADP-induced platelet aggregation (Peng et al., 2011). In this study, we purified a PDE from Taiwan cobra venom (NA_PDE) by using gel filtration, ion exchange and affinity chromatography and its full length amino acid sequence (853 residues) was characterized from PDE-encoding cDNA. Sequence analysis reveals that NA_PDE belongs to Ectophosphodiesterase/nucleotide phosphohydrolase family (ENPP) (Greiner et al., 2013). Like ENPP, the purified NA_PDE hydrolyses ATP/ADP into AMP and PPi/Pi, GTP into GMP and PPi, CTP into CMP and PPi, UTP into UMP and PPi and also NAD into AMP and NMN. Compared to trimeresurus stejnegeri of Viperidae and ENPP1, NA_PDE showed a stronger enzymatic activity in hydrolysis of ATP. In addition, NA_PDE crystal structure resembles ENPP1 architecture and reveals a characteristic bimetallic (two zincs) active site and a nucleotide-binding pocket. These results provide the structural and functional insights of NA_PDE catalytic mechanism for digestion of nucleotides. Herewith we propose that NA_PDE might play a role in reducing immune system as it is known that ATP will stimulate the immune system (Akio & Michail, 2014).