Analysis of Nanobody-Epitope Interactions in Living Cells via Quantitative Protein Transport Assays.

Over the past few decades, quantitative protein transport analyses have been used to elucidate the sorting and transport of proteins in the endomembrane system of plants. Here, we have applied our knowledge about transport routes and the corresponding sorting signals to establish an in vivo system for testing specific interactions between soluble proteins.Here, we describe the use of quantitative protein transport assays in tobacco mesophyll protoplasts to test for interactions occurring between a GFP-binding nanobody and its GFP epitope. For this, we use a secreted GFP-tagged α-amylase as a reporter together with a vacuolar-targeted RFP-tagged nanobody. The interaction between these proteins is then revealed by a transport alteration of the secretory reporter due to the interaction-triggered attachment of the vacuolar sorting signal.