Maturation of adenovirus primes the protein nano-shell for successful endosomal escape

The ability of adenoviruses to infect a broad range of species has spurred a growing interest in nanomedicine to use adenovirus as a cargo delivery vehicle. While successful maturation of adenovirus and controlled disassembly are critical for efficient infection, the underlying mechanisms regulating these processes are not well understood. Here, we present Atomic Force Microscopy nanoindentation and fatigue studies of adenovirus capsids at different maturation stages to scrutinize their dynamic uncoating properties. Surprisingly, we find that the early intermediate immature (lacking DNA) capsid is mechanically indistinguishable in both break force and spring constant from the mature (containing DNA) capsid. However, mature and immature capsids do display distinct disassembly pathways, as revealed by our mechanically-induced fatigue analysis. The mature capsid first loses the pentons, followed by either long-term capsid stability or abrupt and complete disassembly. However, the immature capsid has a stable penton region and undergoes a stochastic disassembly mechanism, thought to be due to the absence of genomic pressure. Strikingly, the addition of the genome alone is not sufficient to achieve penton destabilization as indicated by the penton stability of the maturation-intermediate mutant, G33A. Full penton destabilization was achieved only when the genome was present in addition to the successful maturation-linked proteolytic cleavage of preprotein VI. Therefore these findings strongly indicate that maturation of adenovirus in concert with genomic pressure induces penton destabilization and thus, primes the capsid for controlled disassembly. This latter aspect is critical for efficient infection and successful cargo delivery.