Isolation and Characterization of a Dual Prenylated Rab and VAMP2 Receptor

Rab GTPases have been implicated in intracellular vesicle trafficking. Using the yeast two-hybrid screen, we have isolated a rat clone that interacts with Rab3A as well as with Rab1. The gene encodes a 20.6-kDa protein with two extensive hydrophobic domains and is broadly expressed in all tissues. This protein binds to prenylated Rab GTPases but not to other small Ras-like GTPases such as the Rho/Rac family. This prenylated Rab acceptor (PRA1) also binds specifically to the synaptic vesicle protein VAMP2 (or synaptobrevin II) but shows no affinity for VAMP1 or cellubrevin in both the yeast two-hybrid system and in vitro binding assays. This specificity resides, in part, in the proline-rich domain of VAMP2 as a chimera containing this domain of VAMP2 fused to VAMP1 is able to bind to PRA1. The transmembrane domain of VAMP2 is also essential as its deletion abolished binding to PRA1. Replacement of the deleted VAMP2 transmembrane domain by a CAAX prenylation signal can not restore binding to PRA1. This interaction is therefore distinct from that required for VAMP2 binding to either syntaxin or both syntaxin and SNAP-25. Deletion analysis on PRA1 indicates that the critical Rab- and VAMP2-interacting residues reside in two regions: the amino-terminal residues 30–54 and the extreme carboxyl-terminal domain. This dual Rab and VAMP2 binding characteristic suggests that PRA1 may serve to link these two protein families in the control of vesicle docking and fusion.