Visualization of Protein Interactions in Living Cells

Imaging of Receptor Dimers in Zebrafish and Living Cells via Aptamer Recognition and Proximity-Induced Hybridization Chain Reaction

On cell-membrane surfaces, receptor-protein dimers play fundamental roles in many signaling pathways that are crucial for normal biological processes and cancer development. Efficient and sensitive analysis of receptor dimers in the native environment is highly desirable. Herein, we present a strategy for amplified imaging of receptor dimers in zebrafish and living cells that relies on aptamer recognition and proximity-induced hybridization chain reaction. Taking advantage of specific aptamer recognition and enzyme-free signal amplification, this strategy is successfully applied to the visualization of c-Met-receptor dimers in an HGF-independent or -dependent manner. Therefore, the developed imaging strategy paves the way for further investigation of the dimerization or oligomerization states of cell-surface receptors and their corresponding activation processes in zebrafish and living cells.

Detection of protein interactions during virus infection by bimolecular fluorescence complementation

The bimolecular fluorescence complementation (BiFC) allows not only the investigation of protein interactions but also the visualization of protein complexes in living cells. This method is based on two nonfluorescent fragments of fluorescent proteins (FPs) which can reassemble into a fluorescent complex. The formation of the fluorescent complex requires association of the nonfluorescent fragments which is facilitated by their fusion to two proteins that interact with each other. It is necessary to confirm the specificity of the BiFC signal, e.g., by using proteins with a mutated interaction site. Here, we describe a BiFC protocol adapted for the investigation of protein-protein interactions during herpesvirus infection.

Development of a robust cell-based high-throughput screening assay to identify targets of HIV-1 viral protein R dimerization

Targeting protein-protein interactions (PPI) is an emerging field in drug discovery. Dimerization and PPI are essential properties of human immunodeficiency virus (HIV)-1 proteins, their mediated functions, and virus biology. Additionally, dimerization is required for the functional interaction of HIV-1 proteins with many host cellular components. In this study, a bimolecular fluorescence complementation (BiFC)-based screening assay was developed that can quantify changes in dimerization, using HIV-1 viral protein R (Vpr) dimerization as a "proof of concept." Results demonstrated that Venus Vpr (generated by BiFC Vpr constructs) could be competed off in a dose-dependent manner using untagged, full-length Vpr as a competitor molecule. The change in signal intensity was measured quantitatively through flow cytometry and fluorescence microscopy in a high content screening assay. High content imaging was used to screen a library of small molecules for an effect on Vpr dimerization. Among the tested molecules, a few of the small molecules demonstrate an effect on Vpr dimerization in a dose-dependent manner.