Importance of the Rab3a-GTP binding domain for the intracellular stability and function of Rabphilin3a in secretion

J Neurochem. 1997 Jul;69(1):164-73. doi: 10.1046/j.1471-4159.1997.69010164.x.


We had previously demonstrated that Rab3a-GTP inhibits and the Rab3a-binding protein Rabphilin3a enhances secretion in bovine chromaffin cells. In this study, we investigated the role of Rab3a-GTP binding in the intracellular expression and the function of Rabphilin3a in regulated exocytosis in bovine chromaffin cells. Using transient transfections, we found that a minimal domain, Rp(51-190), that inhibits secretion coincides with a minimal domain that effectively binds Rab3a-GTP and allows intracellular stability of the construct. This domain includes a cysteine-rich, Zn2+-binding domain whose integrity is also required for Rab3a-GTP binding and the ability to inhibit secretion. A Rabphilin3a mutant, containing both C2 domains but defective in Rab3a-GTP, and wild-type Rabphilin3a both localized to chromaffin granules and stimulated secretion similarly despite lessened intracellular expression of the mutant protein. The data are consistent with a sequence of events in which a Rab3a-GTP x Rabphilin3a complex forms on the secretory granule as a precursor in a pathway that enhances secretion. The complex dissociates (perhaps because of GTP hydrolysis) to permit the enhancement of secretion by Rabphilin3a.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding Sites / physiology
  • Biological Transport / physiology
  • Cattle
  • Chromaffin Cells / chemistry
  • Chromaffin Cells / metabolism*
  • Chromaffin Cells / ultrastructure
  • Cytoplasmic Granules / chemistry
  • Cytoplasmic Granules / metabolism
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism*
  • Gene Deletion
  • Gene Expression / physiology
  • Guanosine Triphosphate / chemistry
  • Guanosine Triphosphate / metabolism*
  • Mutagenesis / physiology
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Protein Structure, Tertiary
  • Zinc / metabolism
  • rab3 GTP-Binding Proteins


  • Nerve Tissue Proteins
  • Guanosine Triphosphate
  • GTP-Binding Proteins
  • rab3 GTP-Binding Proteins
  • Zinc