Use of split-dihydrofolate reductase for the detection of protein-protein interactions and simultaneous selection of multiple plasmids in Plasmodium falciparum

Nanobody-assisted nanoluciferase fragment complementation for in situ measurement and visualization of endogenous protein-protein interaction

Here, we developed nanobody-assisted nanoluciferase fragment complementation for in situ measurement and visualization of endogenous protein-protein interaction (NanaPPI). When an interaction occurs, primary antibodies for two proteins bring the proximity of secondary nanobody-fused small/large fragment to reassemble into an intact NanoLuc variant, thus transforming interaction events to luminescent signals in situ with high sensitivity. Compared to proximity ligation assay, NanaPPI has a similar signal-to-background ratio, but it is more convenient with faster procedures, easier readout and lower cost. NanaPPI not only allows direct detection of low abundant interactions, but also visualizes protein-protein interaction events in fixed cells and tissue sections. By applying NanaPPI, disruption of PPIs by inhibitors and distinct PPI levels under physiological or pathological conditions, can be quantified efficiently. Unknown interactions YTHDF2/G3BP1 and RNA m6A/G3BP1 can be also identified by NanaPPI under unstressed conditions, with drastic increasing under arsenite stress. The interaction between RNA m6A and G3BP1 is largely reduced upon YTHDF2 knockdown, indicating YTHDF2 mediates the enrichment of m6A-modified mRNA in stress granules. In conclusion, NanaPPI provides a robust, easy, and economical method for rapid in situ measurement of PPIs in cells and tissues, which has great potential for new PPI identification, PPI inhibitor screening, and PPI biomarker-based diagnosis in clinics.

Near-Infrared Luciferase Complementation Assay with Enhanced Bioluminescence for Studying Protein-Protein Interactions and Drug Evaluation Under Physiological Conditions

Identification of protein-protein interactions (PPIs) that occur in various cellular processes helps to reveal their potential molecular mechanisms, and there is still an urgent need to develop the assays to explore PPIs in living subjects. Here, we reported a near-infrared split luciferase complementation assay (SLCA) with enhanced bioluminescence produced by cleaving a luciferase, Akaluc, for exploring and visualizing PPIs in living cells and live mice. Compared with the previously developed and widely used red SLCA based on split firefly luciferase (Fluc-SLCA), the signal intensities for PPI recognition in living cells and live mice of the Akaluc-SLCA increased by ∼3.79-fold and ∼18.06-fold in the measured condition, respectively. Additionally, the interactions between the nucleocapsid protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and cellular RNA processing proteins were identified, and the drug evaluation assays were also performed in living cells using Akaluc-SLCA. This study provides a new tool in the near-infrared region for the identification of PPIs in living cells and in vivo and new information for the understanding and treatment of SARS-CoV-2.

Protein-fragment complementation assays for large-scale analysis of protein-protein interactions

Protein-protein interactions (PPIs) orchestrate nearly all biological processes. They are also considered attractive drug targets for treating many human diseases, including cancers and neurodegenerative disorders. Protein-fragment complementation assays (PCAs) provide a direct and straightforward way to study PPIs in living cells or multicellular organisms. Importantly, PCAs can be used to detect the interaction of proteins expressed at endogenous levels in their native cellular environment. In this review, we present the principle of PCAs and discuss some of their advantages and limitations. We describe their application in large-scale experiments to investigate PPI networks and to screen or profile PPI targeting compounds.