BPS2026 – Actin-aided viral trafficking on plasma membrane directly observed with 3D single-virus tracking

Understanding how viruses exploit the host cytoskeleton at the cell membrane remains a key challenge in viral entry. While “virus surfing” on actin-rich protrusions, such as filopodia, is well-documented, direct observation of viral dynamics on non-protrusive actin structures has been limited by the difficulty of resolving nanoscale motion along the three-dimensional cell surface. Here, we employed three-dimensional tracking and imaging microscopy (3D-TrIm) together with photostable StayGold-labeled SARS-CoV-2 virus-like particles to achieve long-term, high-resolution single-virus tracking in live cells. This platform revealed a previously under-characterized trafficking mode: linear, actin-dependent viral motion along the plasma membrane preceding internalization. Quantitative analysis demonstrated that this trafficking is receptor-dependent, positively correlated with ACE2 expression levels, and strongly suppressed by perturbation of actin polymerization or myosin activity but largely unaffected by microtubule inhibition. These results illustrate the power of advanced single-virus tracking to uncover new modes of virus-cell interaction at tens of nanometers precision and millisecond timescales. Our findings also expand the paradigm of actin-mediated viral motility beyond filopodial surfing, highlighting a general mechanism by which viruses hijack actin networks underlying the plasma membrane to explore the cell surface and relocate toward optimal entry sites.