Visualization of single receptor molecules bound to human rhinovirus under physiological conditions

Dynamic force microscopy (DFM) was used to image human rhinovirus HRV2 alone and complexed with single receptor molecules under near physiological conditions. Specific and site-directed immobilization of HRV2 on a model cell membrane resulted in a crystalline arrangement of virus particles with hexagonal symmetry and 35 nm spacing. High-resolution imaging of the virus capsid revealed about 20 resolvable structural features with 3 nm diameters; this finding is in agreement with protrusions seen by cryo-electron microscopy. Binding of receptor molecules to individual virus particles was observed after injection of soluble receptors into the liquid cell. Virus-receptor complexes with zero, one, two, or three attached receptor molecules were resolved. The number of receptor molecules associated to virions increased over time. Occasionally, dissociation of single receptor molecules from viral particles was also observed.