Abstract

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. ### Competing Interest Statement The authors have declared no competing interest. Japan Society for the Promotion of Science, https://ror.org/00hhkn466, 20H00327, 24H00402, 24K04849, PE20014, 24K18450 Japan Agency for Medical Research and Development, https://ror.org/004rtk039, JP24gm1610009 Japan Science and Technology Agency, https://ror.org/00097mb19, JPMJPR20E3, JPMJPR23J2