Viruses are remarkable self-assembled nanobiomaterial-based machines, exposed to a wide range of pH values. Extreme pH values can induce dramatic structural changes, critical for the function of the virus nanoparticles, including assembly and genome uncoating. Tuning cargo-capsid interactions is essential for designing virus-based delivery systems. Here we show how pH controls the structure and activity of wild-type simian virus 40 (wtSV40) and the interplay between its cargo and capsid. Using cryo-TEM and solution X-ray scattering, we found that wtSV40 was stable between pH 5.5 and 9, and only slightly swelled with increasing pH. At pH 3, the particles aggregated, while capsid protein pentamers continued to coat the virus cargo but lost their positional correlations. Infectivity was only partly lost after the particles were returned to pH 7. At pH 10 or higher, the particles were unstable, lost their infectivity, and disassembled. Using time-resolved experiments we discovered that disassembly began by swelling of the particles, poking a hole in the capsid through which the genetic cargo escaped, followed by a slight shrinking of the capsids and complete disassembly. These findings provide insight into the fundamental intermolecular forces, essential for SV40 function, and for designing virus-based nanobiomaterials, including delivery systems and antiviral drugs.
Bibliographical noteFunding Information:
We thank Daniel Harries for helpful discussions. We thank the Desy synchrotron at Hamburg, beamline P12 (D. Svergun and his team), the Soleil synchrotron, Swing beamline (J. Perez and his team), and the ESRF synchrotron, ID02 beamline (T. Narayanan and his team) for provision of synchrotron radiation facilities and for assistance in using the beamlines. This project was supported by the Israel Science Foundation (656/17), the United States-Israel Binational Science Foundation (2016311), and the NIH (Award Number R01GM108021). RA acknowledges support from the Kaye-Einstein fellowship foundation.
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