Bemisia tabaci whiteflies are vectors of several devastating plant viruses of the genus, Begomovirus. These pests have damaged millions of dollars worth of agriculture in California, Arizona, Texas, and Florida. They feed on the phloem of an infected plant whereby the whitefly obtains the virus and allows it to pass through the digestive and salivary systems before it is transmitted to the next plant host. Our research focuses on digestive proteases hypothesized to be present in the whitefly. Previously using a spectrophotometric assay and synthetic protease substrates, we identified proteolytic activity in whitefly whole-body extracts and demonstrated optimal activity at pH 5.5. Trypsin and chymotrypsin inhibitors were tested and found to be ineffective toward this proteolytic activity. Furthermore, enzymatic activity was found in whole-body whitefly extracts using native and denaturing, reducing gelatin/polyacrylamide gel electrophoresis (PAGE) assays. We now hypothesize that the activity is cysteine protease-like due to its acidic nature and its molecular weight of 40 kDa. Pseudo-two dimensional gel electrophoresis confirmed that the activated protease is a single polypeptide with a molecular weight similar to that of the insect cysteine protease, cathepsin B. Once fully characterized, we plan to determine if the protease has digestive and/or homeostatic functions by localizing the protease activity in different insect tissues. If the proteases are digestive enzymes, future experiments will focus on determining how a virus that has a protein coat can survive in the digestive system in the presence of proteases.
Species 1: Homoptera Aleyrodidae Bemisia tabaci (silverleaf whitefly (B-biotype))
Keywords: protease, cathepsin B
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