Recombinant Antitoxic and Antiinflammatory Factor from the Nonvenomous Snake Python reticulatus:  Phospholipase A2 Inhibition and Venom Neutralizing Potential

From the serum of the nonvenomous snake Python reticulatus, a new phospholipase A2 (PLA2) inhibitor termed phospholipase inhibitor from python (PIP) was purified by sequential chromatography and cloned to elucidate its primary structure and fundamental biochemical characteristics. A cDNA clone encoding PIP was isolated from the liver total RNA by reverse transcriptase−polymerase chain reaction (RT-PCR). It contained a 603 bp open reading frame that encoded a 19-residue signal sequence and a 182-residue protein. PIP showed about 60% sequence homology with those PLA2 inhibitors having a urokinase-type plasminogen activator receptor-like domain structure. PIP was also functionally expressed as a fusion protein in Escherichia coli to explore its potential therapeutic significance. The recombinant PIP was shown to be identical to the native form in chromatographic behavior and biochemical characteristics. Both the native and recombinant PIP appear to exist as a hexamer of 23-kDa subunits having an apparent molecular mass of ∼140 kDa. PIP showed ability to bind to the major PLA2 toxin (daboiatoxin, DbTx) of Daboia russelli siamensis at 1−2-fold molar excess of inhibitor to toxin. It exhibited broad spectra in neutralizing the toxicity of various snake venoms and toxins and inhibited the formation of edema in mice. Our data demonstrate the venom neutralizing potential of the recombinant PIP and suggest that the proline-rich hydrophobic core region may play a role in binding to PLA2.