Isolation of Antipathogenic Proteins from Plants

Plants produce a diversity of proteins with antipathogenic activities. These proteins comprise among others, (i) ribonucleases, (ii) antifungal proteins, (iii) lectins and (iv) trypsin inhibitor with antiviral, antifungal and anticancer activities. The aim of this project was to isolate antipathogenic plant proteins including a ribonuclease from American ginseng branch roots, a trypsin inhibitor from rambutan seeds, defensin-like antifungal peptides from borlotti beans and king pole beans, and lectins from borlotti beans, Japanese large pinto beans and Pseudostellaria heterophylla..;The isolated 26-kDa ginseng branch root ribonuclease was monomeric with a novel N-terminal amino acid sequence. It exhibited maximal robonucleolytic activity toward yeast tRNA at pH 5 and 60°C. It inhibited proliferation of MCF7 human breast cancer cells and HepG2 human hepatoma cells. It also inhibited the activity of HIV-1 reverse transcriptase.;Both borlotti bean lectin and Japanese large pinto bean lectin were dimeric with a subunit molecular mass of 32-kDa. They were stable from 0°C to 60°C and from pH 3 to pH 12. Borlotti bean lectin was xylose-specific whereas Japanese large pinto bean lectin was galactose-specific. The 33-kDa Pseudostellaria heterophylla lectin could not be inhibited by the simple sugars tested. It was stable from 0°C to 60°C and from pH 2 to 5. All three isolated lectins suppressed proliferation of MCF7 and HepG2 cells and inhibited HIV-1 reverse transcriptase.;The isolated 21-kDa rambutan trypsin inhibitor has relatively high pH stability and thermostability, and exhibited HIV-1 reverse transcriptase inhibitory activity and antiproliferative activity toward a variety of tumor cells. The isolated 5447-Da king pole bean defensin-like peptide inhibited fungal growth.