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A Glycolytic Enzyme, Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH), is Required for Insect Cellular Immunity, which is Revealed by a Viral Gene, CpBV-CrV1
Insect immunity is innate and consists of cellular and humoral immune responses. Cellular immune response usually requires hemocyte-spreading behavior, which is accompanied by cytoskeletal rearrangement. A glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), catalyzes an oxidation reaction of glyceraldehyde-3-phosphate to 1,3-biphosphoglycerate in the cytosol. Another function of GAPDH in mammalian cell is to bind C-terminal α-tubulin to facilitate cytoskeletal arrangement. An immunoprecipitation (IP) of viral protein, CpBV-CrV1, against hemocyte protein lysate revealed that CpBV-CrV1 binds to GAPDH, identified by MALDI-TOF analysis. RNA interference (RNAi) of GAPDH significantly suppressed cellular immune response, but neither RNAi of hexokinase nor aldolase suppressed the cellular immune response. A common molecular motif of CpBV-CrV1 and a-tubulin at C-terminal region supported the IP analysis. To test the role of α-tubulin motif in CpBV-CrV1, point mutations of CpBV-CrV1 were applied and resulted in loss of the biological activity of CpBV-CrV1. Furthermore, an immunofluorescence assay indicates CpBV-CrV1 colocalized with a-tubulin in hemocytes collected from Plutella xylostella parasitized by Cotesia plutellae possessing C. plutellae bracovirus (CpBV). This result suggests that GAPDH plays a critical role in hemocyte-spreading behavior during immune challenge, and it is a molecular target of the pathogenic virus.
