Abstract
Plants have developed various defense strategies against insect, bacterial and fungal attack. Interestingly, many small, highly basic and cysteine-rich proteins are involved in the defense mechanisms. These defense related proteins include hevein, thionins, knottin-like peptides, plant non-specific lipid transfer proteins (nsLTPs) and plant defensins. All of them adopt a compact fold stabilized by 2-6 disulfide bonds. Among these defense proteins, both nsLTPs and plant defensins have eight conserved cysteines forming four disulfide bonds. NsLTPs are well known for their ability to bind a variety of lipid molecules and catalyze the transfer of lipids between membranes in vitro. They are also involved in other biological functions such as involvement in defense against pathogens, biosynthesis of cutin, and managing abiotic stress conditions imparted by temperature and drought situation. NsLTPs are subdivided into two different isoforms with molecular mass of 9kDa (nsLTP1) and 7kDa (nsLTP2). We have isolated nsLTP1 and nsLTP2 from rice seeds. Here, the purification, characterization, lipid-transfer and lipid-binding of nsLTPs are reported. Plant defensins are well known for their ability to exhibit antifungal activity against a broad range of fungi including various plant pathogens. They are a family of cysteine-rich, basic peptides of 45 to 54 amino acids isolated from many plants including wheat, barley, pea, radish, sorghum and mung bean. Plant defensins also have additional biological activities including inhibition of alpha-amylase, of trypsin, of sodium channel and of protein synthesis in cell-free system. Recently, an insecticidal plant defensin designated VrD1 was reported exhibiting in vitro insect-resistant activity against bruchid. Here we report the three-dimensional structure of VrD1 as determined by NMR spectroscopy. Furthermore, VrD1 was confirmed to inhibit Tenebrio molitor alpha-amylase implying that VrD1 exhibited insecticidal activity through inhibition of alpha-amylase. Computational docking experiments were used to study the interactions between VrD1 and insect alpha-amylase, and these results provide useful interaction information that may improve the insecticidal activity of VrD1.