Probing Protein-Protein Interactions In A Single Virus: Application To Hiv Integrase Oligomerization

Direct measurement of protein-protein interactions (PPIs) in single viruses is crucial to provide insight into viral biology, replication and pathogenesis in a spatial and time-resolved manner. We report on an imaging method based on Förster resonance energy transfer (FRET) with fluorescent proteins (FPs) to probe the oligomerization of the human immunodeficiency virus (HIV) type 1 integrase enzyme (IN) in viral particles and in infected cells. We performed a detailed characterization of fluorescently labeled viruses at the single-FP level and show that the fluorescent content of particles can be accurately controlled. We demonstrate that measuring FRET with FPs inside single virions is feasible and prove that IN forms oligomers in the virus, as well as in HIV-1 viral complexes inside infected cells. Our methodology can be applied to the study of any protein targeted into viral particles and to measure interactions with host proteins in infected cells.