Microscopy allows researchers to interrogate proteins within a cellular context. To deliver protein-specific contrast, we developed a new class of genetically encoded peptide tags called versatile interacting peptide (VIP) tags. VIP tags deliver a reporter to a target protein via the formation of a heterodimer between the peptide tag and an exogenously added probe peptide. We report herein a new VIP tag named MiniVIPER, which is comprised of a MiniE-MiniR heterodimer. We first demonstrated the selectivity of MiniVIPER by labeling three cellular targets: Transferrin receptor 1 (TfR1), histone protein H2B, and the mitochondrial protein TOMM20. We showed that either MiniE or MiniR could serve as the genetically encoded tag. Next, we demonstrated MiniVIPER's versatility by generating five spectrally distinct probe peptides to label tagged TfR1 on live cells. Lastly, we demonstrated two new applications for VIP tags. First, we used MiniVIPER in combination with another VIP tag, VIPER, to selectively label two different proteins in a single cell (e.g., TfR1 with H2B or TOMM20). Second, we used MiniVIPER to translocate a fluorescent protein to the nucleus through in situ dimerization of mCherry with H2B-mEmerald. In summary, MiniVIPER is a new peptide tag that enables multitarget imaging and artificial dimerization of proteins in cells.
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