McArthur, S. J.; Umeda, K.; Kodera, N.

Although the maturation state of dengue virus (DENV) particles is a key determinant of their infectivity, maturation is unusually inefficient. Fully mature and immature DENV particles are well-studied; however, little is known about partially mature particles. Moreover, single-particle structural dynamics and nanomechanical properties are unknown. Here, we observe wildtype and immature DENV particles using a single-particle approach combining high-speed AFM (HS-AFM) and 3D force mapping (3DFM). HS-AFM shows that the conformations of each morphotype are heterogeneous and dynamic in liquid, particularly partially mature virions. Tracking immature prM-E spikes elucidates their dynamic movements, which show intraviral variation and constrained independence. 3DFM measurements suggest that internal DENV structure is also heterogeneous and undergoes maturation-dependent changes, with the nucleocapsid core not occupying the full internal volume of immature virions. This approach complements current structural virology techniques and adds a new dimension to our understanding of the structural properties of viruses.