What it is
The authors combined mass photometry with a single-molecule trapping method to watch individual virus-like particles assemble in real time with molecular resolution. Weak, reversible multivalent interactions steer assembly through a limited set of on-path, topologically closed intermediates, with progress set by the transition rates between them in a sequence of effectively irreversible first-passage events. The particle's symmetry separates the formation of the first closed intermediate from later elongation, giving a nucleation-and-growth mechanism whose final distribution still matches the law of mass action.
Why it matters
Viral capsid assembly is the archetypal self-assembly system, but despite decades of experiments its pathways and dynamics had not been directly observed or quantified. Following single particles as they build explains how the system reliably reaches one final structure despite thousands of available intermediates, and the approach offers a general way to watch multimeric biological machines assemble at the molecular level.
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Filed underBacteriophages and microbial interactions, Polyomavirus and related diseases, SARS-CoV-2 and COVID-19 Research