Tethering assay to assess the physical interaction of Mitofusin proteins in trans.
A, schematic of the differential epitope labeling utilized in the tethering assay. B, mitochondria were isolated from a clonal population of Mfn1WT-FLAG-expressing Mfn1-null cells (Mfn1WT Mfn2+/+), a clonal population of Mfn1WTeGFP-expressing Mfn1-null cells (Mfn1WT Mfn2+/+), a clonal population of Mfn1F202LFLAG-expressing Mfn1-null cells (Mfn1F202L Mfn2+/+), and a clonal population of Mfn1F202L-eGFP-expressing Mfn1-null cells (Mfn1F202L Mfn2+/+) and incubated with BeF3 in the absence or presence of GDP. Following lysis, immunoprecipitation was performed with α-FLAG magnetic beads. Proteins eluted from the beads were subjected to SDS-PAGE and immunoblotted with α-Mfn1. The arrowhead indicates the eGFP protein eluted from FLAG beads. Total (T) represents 3% of the input, flow-through (FT) represents 3% of the unbound protein, and elution (E) represents 40% of the immunoprecipitated protein. C, the percentage of the indicated Mitofusin-eGFP in the elution compared with the total is shown as the mean +S.D. of three independent experiments. D, the percentage of the indicated Mitofusin-FLAG in the elution compared with the total is shown as the mean + S.D. of three independent experiments.