Rungsa_2018_Toxicon_148_74

Vespa tropica, a social wasp locally found in Thailand is responsible for many out off the record accidental stings due to close encounters with human activities and because of the animal's highly potent venom. Phospholipase (PLA) is one of the major proteins commonly found in insect venom. In this work, V. tropica phospholipase was successfully isolated, purified and characterized. Three isoforms PLAs have been purified using reversed phase HPLC, and are named VesT1s (VesT1.01a, VesT1.01b and VesT1.02). They are not glycoproteins. VesT1.01s has a molecular weight of 33.72kDa while for VesT1.02 a mass of 34kDa was found. The deduced sequence of the mature VesT1.02 protein is composed of 301 amino acid residues (1005 bp), including the catalytic triad (Ser-His-Asp), which is similar to other wasp venom PLAs. The 12 cysteine residues found are conserved among venom PLA1. They form six disulfide bonds, and therefore have no free sulfhydryl groups. Based on homology modelling, VesT1.02 belongs to the alpha/beta hydrolase fold family. Its structure is composed of 10 beta-sheets and 11 alpha-helixes, characterized by a beta-strand/epsilonSer/alpha-helix structural motif, which contains the Gly-X-Ser-X-Gly consensus sequence. The shortened lid and shortened beta9 loop, which play important roles in substrate selectivity, cause this enzyme to only exhibit PLA activity. Moreover, these PLAs have been shown to be highly thermally stable after heating at 100 degrees C for 5min. We propose that an inserted Pro residue might be involved in this high thermo-stability.