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Genes Cells. 1997 Apr;2(4):273-88.

A novel function of the C-terminal lipid moieties of Rab3A small G protein implicated in Ca2+-dependent exocytosis--inhibition of interaction with GTP and reduction of this inhibition by phospholipid.

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  • 1Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, Japan.



Rab3A small G protein is implicated in Ca2+-dependent exocytosis. It undergoes posttranslational lipid-modifications at its C-terminal region. These lipid moieties are important for the actions of the regulators of Rab3A, but not for the interaction with its downstream target.


We have found another function of the C-terminal lipid moieties of Rab3A. GTP rapidly associates with the guanine nucleotide-free form of unmodified Rab3A, but not with the same form of modified Rab3A. Moreover, GTP rapidly dissociates from the GTP-bound form of modified Rab3A, but not from the same form of unmodified Rab3A. The association of GTP with the guanine nucleotide-free form of modified Rab3A is stimulated by the Rab3 GDP/GTP exchange protein (Rab3 GEP), and the dissociation of GTP from the GTP-bound form is markedly reduced by synaptic vesicle phospholipid.


These results suggest that the interaction of the lipid moieties of Rab3A with Rab3 GEP or synaptic vesicles is required for the interaction of modified Rab3A with GTP. Moreover, these results - together with the fact that Rabphilin-3A associated with synaptic vesicles inhibits the activity of Rab3 GTPase-activating protein - suggest that the GTP-bound form of modified Rab3A is associated with synaptic vesicles through both Rabphilin-3A and the vesicle phospholipid.

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