Sequencing and two-dimensional structure prediction of a phospholipase A2 inhibitor from the serum of the common tiger snake (Notechis scutatus)

A phospholipase A2 inhibitor has been identified in the serum of the common tiger snake (Notechis scutatus). The inhibitor is composed of two chains, an α-chain and a β-chain, that form a non-covalently associated complex capable of inhibiting the enzymatic activity of all phospholipase A2 enzymes it was tested against. The α and β-chains have been purified to homogeneity, digested and sequenced. From the peptide sequence generated, degenerate PCR primers were designed and used to elucidate the complete cDNA sequence of the chains using 5′ and 3′ RACE PCR. A total of three α-chain isoforms were identified, only one isoform of the β-chain was detected. The two-dimensional structure of the three α-chains and one β-chain were predicted using five prediction programs (discrimination of secondary structure class; nearest neighbour secondary structure, profile network from Heidelberg; self-optimised prediction method from multiple alignment, SSPAL). For each protein chain a consensus prediction was generated. Results are discussed in relation to the function of the protein, and how they may influence the three-dimensional structure of the inhibitor. Additionally, the sequences of several snake phospholipase A2 inhibitors were used as the input for a motif prediction algorithm (MEME). The results are discussed in relation to the activity of these proteins.