Small GTPases of the Rab family are key regulators of membrane trafficking. Monoclonal antibodies are useful tools for identifying proteins that interact with other proteins and for examining their tissue distribution. We selected a monoclonal antibody against Rab8 of Bombyx mori L. It specifically recognized amino acid residues 30-109, which are conserved among Rab8 proteins, and did not recognize any other Rab proteins. Western blotting using the antibody revealed one band in the brains of B. mori and rat. Far-Western blotting analysis detected three proteins interacting with Rab8. These results indicate that this antibody is useful for clarifying the physiological function of Rab8 of B. mori and other species. This is a report of a study on a monoclonal antibody against insect Rab protein.
Small GTPases of the Rab family act as essential regulators of vesicle transport pathways. Five Rab cDNA clones (BRab1, 7, 8, 11 and 14) from Bombyx mori were expressed in Escherichia coli as a thioredxin or glutathione sulfotransferase fusion protein. After purification, the fusion protein was tested for phosphorylation using protein kinase C (PKC). Results indicate that all of them were phosphorylated in vitro. The phosphorylation site of BRab1 was determined by mass-spectrometric analysis, which identified that Ser-17 of BRab1 was phosphorylated by PKC. Deletion and site-directed mutagenesis indicated that Ser-111of BRab8, in addition to Ser-17, was newly phosphorylated. Further immunohistochemical analysis using antibodies against Rab8 indicated that there are some Rab8 immunoreactive cells close to the neuropeptide secreting cells. This result suggests that in insects Rab proteins are regulated by phosphorylation and at least some of them are involved in neuropeptide secretion.