Small GTP-binding proteins in the brain-corpus cardiacum-corpus allatum complex of the silkworm, Bombyx mori: involvement in the secretion of prothoracicotropic hormone.

摘要

At least three GTP-binding proteins (G-proteins), 28, 25, and 21 kDa, were found in the brain-corpus cardiacum-corpus allatum complex (BR-CC-CA) of the silkworm, Bombyx mori. They bound to GTP and GDP specifically among the nucleotides tested, indicating that these proteins were small G-proteins. The 25 kDa G-protein showed a cross-reactivity to anti-rab3A antibody, but did not cross-react with anti-rhoA, rab3B, and anti-ras antibodies. However, the 28 and 21 kDa G-proteins showed no cross-reactivity to any of those antibodies tested. Immunoblot analysis using the anti-rab3A antibody demonstrated that the 25 kDa G-protein was detected preferentially in the BR-CC-CA, and to some extent in the sub-oesophageal ganglion, but not in the salivary gland,fat body, prothoracic gland, and oesophagus. The results suggested that the 25 kDa G-protein was a member of the rab family of G-proteins. Furthermore, 1 mM GTPgammaS capable of activating G-proteins induced BR-CC-CA to release PTTH under the conditionsthat stimulation of the PTTH release with hetero-trimeric G-protein was suppressed. These results indicate that the small G-proteins may possibly contribute to PTTH release in Bombyx mori.