Phosphodiesterase from Vipera lebetina venom - structure and characterization.

Nucleases and phosphatases are ubiquitous but mostly marginal components of snake venoms. These proteins have been studied quite extensively but up to now no data regarding their amino acid sequences confirmed at protein level have been published. The present study deals with purification, characterization, and structural properties of a phosphodiesterase from Vipera lebetina venom (VLPDE). The VLPDE with molecular mass of about 120 kDa hydrolyses ADP but not ATP and 5'-AMP. The aggregation of platelets induced by ADP or collagen is dose-dependently inhibited by VLPDE. The cloning and sequencing of the VLPDE-encoding cDNA resulted in 2772-nt sequence with ORF of 2556 nt. The translated sequence comprises 851 amino acids including the 23-amino acid signal peptide. VLPDE is synthesized as a 828-amino acid single-chain protein but subsequently cleaved to form a two-chain protein held together with disulfide bonds. In reducing conditions the enzyme behaves like a heterodimeric protein but, differently from the real heterodimers, it is synthesized as a single-chain protein. VLPDE is the first snake venom phosphodiesterase with established and confirmed primary structure.