Cuellar JL, Meinhoevel F, Höhne M, Donath E (2010): Size and Mechanical Stability of Norovirus Capsids depend on pH - A Nanoindentation Study
J. Gen. Virol. 91 (10): 2449-2456. Epub Jun 30.

Norovirus - like particles (VLPs), were imaged with Atomic Force Microscopy. The mechanical stability of the VLPs was probed by nanoindentation at pH values ranging from 2 - 10. This range includes pH values of the natural environment during the life cycle of noroviruses. The resistivity of VLPs toward indentation was constant at acidic and neutral pH. The young modulus was of the order of 30 MPa. At basic pH the compliance of the capsid increased along with an increase of the diameter. This specific pH-dependent mechanical response of the capsid may have a relation to mechanisms controlling uptake and release of the RNA during infection. Consecutive indentations with pressures up to 300 bars demonstrated the ability of the capsids to fully recover from deformations comparable with the size of the capsid. The capsids can be viewed as nanocontainers with an inbuilt self-repair mechanism. At pH 10 the capsids lost their stability and were irreversibly destroyed after one single indentation.