Purification and Interaction Analysis of a Plant-Specific RAB5 Effector by In Vitro Pull-Down Assay.

RAB GTPases regulate membrane traffic by interacting with effector proteins in the GTP-bound active form. RAB GTPases are highly conserved in a broad range of eukaryotic organisms, while land plants and some green algal species possess a plant-specific RAB5 group. A plant-specific RAB5 in Arabidopsis called ARA6 was shown to regulate a characteristic trafficking route, and participate in abiotic and biotic stress responses. The identification of ARA6 effectors is a powerful strategy to get insights into the molecular basis of ARA6 functions. Recently, we identified an ARA6 effector, PLANT-UNIQUE RAB5 EFFECTOR 2 (PUF2), and characterized its functions by biochemical means. PUF2 was hardly expressed as a recombinant protein in the bacterial system, but we solved this problem by optimizing the codon usage of PUF2 CDS to suite for expression in Escherichia coli. Here, we present the protocol we employed to purify PUF2 protein, and to test its nucleotide state-specific interaction with ARA6 by in vitro pull-down assay. This approach would be extended to analyze the molecular functions of other effector proteins of RAB GTPases.