Lemon-shaped archaeal viruses are found in some of the most extreme environments (80 °C, pH ~2). They undergo dramatic architectural rearrangement into tubular structures that could be facilitated by their unique helical structure built of seven strands of major capsid protein. Little is known about the mechanical properties compatible with this alteration and their ability to thrive in such environments. Our experiments reveal that lemon-shaped virions withstand deformations of 80%, collapsing wall-to-wall without damage. Our data suggest a protein shell with membrane-like fluidity and a liquid genomic cargo that only fills ~11% of the virion internal volume. These features are in stark contrast with those known for other viruses with protein capsids, stressing the interplay between mechanics, structure, and function. [Full article]
