A novel protein from the serum of Python sebae, structurally homologous to γ-phospholipase A2 inhibitor, displays antitumor activity
Résumé
Cytotoxic and antitumors factors have been documented in the venom of snakes, while little information is available on the identification of cytotoxic products in the snake serum. In this study, we purified and characterized a new cytotoxic factor from serum of the non venomous Phyton sebae, endowed with antitumor activity. The serum of the P. sebae, termed PSS, exerted a cytotoxic activity and reduced dose dependently the viability of several different tumor cell lines. In a model of human squamous cell carcinoma xenograft (A431), subcutaneous injection of PSS in proximity of the tumor mass reduced by 20% tumor volume. Fractionation of PSS by ion-exchange chromatography yielded an active protein fraction, F5, which significantly reduced tumor cell viability in vitro, and strikingly tumor growth in vivo. F5 is composed of P1 and P2 subunits interacting in a 1:1 stoichiometric ratio to form a hetero-tetramer in equilibrium with a hexameric form, which retained the biological activity only when assembled. The two peptides share sequence similarity with type-γ phospholipase A2 (PLA2) inhibitor (PLI-γ) from P. reticulatus, PIP, existing as a homo-hexamer. More importantly, while PIP inhibits the hydrolytic activity of PLA2, the anti-PLA2 function of F5 is negligible. Using high resolution mass spectrometry, we covered 87 and 97% sequence of P1 and P2. In conclusion, here we have identified and thoroughly characterized a novel protein displaying high sequence similarity with PLI-γ molecule and possessing remarkable cytotoxic and antitumor effects, that can be exploited for potential pharmacological applications.
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