The HIV-1 capsid is a protein shell protecting the viral genome after entry into the host cell. The virus has evolved to exploit host cofactors that interact with the incoming capsid core to regulate reverse transcription, nuclear import and integration of viral cDNA into preferred regions of the host chromosome. Conversely the cell has evolved restriction factors that recognise the capsid lattice and block infection. Spatiotemporal control of capsid disassembly ("uncoating") plays a central role in these competing processes: Host cofactors function by controlling capsid stability to evade detection by innate immune sensors while restriction factors lead to premature uncoating (or prevent uncoating entirely), resulting in degradation of the virus.
Structural approaches have yielded high-resolution snapshots of host cell proteins interacting with the capsid lattice. However, a detailed understanding of the dynamics of these interactions and how they lead to changes in the lattice is still missing. Here we use fluorescence microscopy to visualise the dynamic interactions between host cell protein or drugs and viral capsids in real time. Single-molecule analysis of individual capsids allows us to overcome the challenges associated with the heterogeneity of viral particles and resolve distinct steps in the uncoating process without the need for synchronisation. Our study reveals that different interactors binding to the same site of the lattice can have opposing effects on different phases of viral uncoating.