The small G protein Rab3A plays an important role in the regulation of neurotransmitter release. The crystal structure of activated Rab3A/GTP/Mg2+bound to the effector domain of rabphilin-3A was solved to 2.6 Å resolution. Rabphilin-3A contacts Rab3A in two distinct areas. The first interface involves the Rab3A switch I and switch II regions, which are sensitive to the nucleotide-binding state of Rab3A. The second interface consists of a deep pocket in Rab3A that interacts with a SGAWFF structural element of rabphilin- 3A. Sequence and structure analysis, and biochemical data suggest that this pocket, or Rab complementarity-determining region (RabCDR), establishes a specific interaction between each Rab protein and its effectors. RabCDRs could be major determinants of effector specificity during vesicle trafficking and fusion.
Ostermeier, C., & Brunger, A. T. (1999). Structural Basis of Rab Effector Specificity. Cell, 96(3), 363–374. https://doi.org/10.1016/s0092-8674(00)80549-8