Herpes Virus Genome, The Pressure Is On

David W Bauer,Jamie B Huffman,Alex Evilevitch,Fred L Homa

doi:10.1021/ja404008r

Abstract

Herpes simplex virus type 1 (HSV-1) packages its micrometers-long double-stranded DNA genome into a nanometer-scale protein shell, termed the capsid. Upon confinement within the capsid, neighboring DNA strands experience repulsive electrostatic and hydration forces as well as bending stress associated with the tight curvature required of packaged DNA. By osmotically suppressing DNA release from HSV-1 capsids, we provide the first experimental evidence of a high internal pressure of tens of atmospheres within a eukaryotic human virus, resulting from the confined genome. Furthermore, the ejection is progressively suppressed by increasing external osmotic pressures, which reveals that internal pressure is capable of powering ejection of the entire genome from the viral capsid. Despite billions of years of evolution separating eukaryotic viruses and bacteriophages, pressure-driven DNA ejection has been conserved. This suggests it is a key mechanism for viral infection and thus presents a new target for antiviral therapies.

Highlights

Herpes simplex virus type 1 (HSV-1) is one of 8 human pathogenic herpesviruses known today, including Epstein-Barr virus (EBV), cytomegalovirus (CMV), and Kaposi’s sarcomaassociated herpesvirus (KSHV)[1]
Southern blot analysis confirms that trypsin-induced DNA ejection follows the expected directionality, with ejection beginning at the S end of the HSV-1 genome[29] (Supporting Information Figure S2)
When HSV-1 capsids are opened by trypsin treatment in the presence of polyethylene glycol (PEG), DNA exits the capsid until the decreasing ejection force equals the resisting force imposed by the external osmotic pressure

Summary

Introduction

Herpes simplex virus type 1 (HSV-1) is one of 8 human pathogenic herpesviruses known today, including Epstein-Barr virus (EBV), cytomegalovirus (CMV), and Kaposi’s sarcomaassociated herpesvirus (KSHV)[1]. The HSV-1 DNA packaging process resembles that of the more extensively studied dsDNA bacteriophages[11,12] (viruses that infect bacteria), which package their microns-long genome into a nanometer-scale capsid This confinement requires DNA to bend along radii that are energetically unfavorable given its 50 nm persistence length*, creating bending stress on the packaged genome[13,14,15]. The energetics and mechanical properties associated with tight genome confinement have been probed using microcalorimetry[20] and atomic force microscopy (AFM)[8,21,22] We have investigated this internal pressure for HSV-1 using solutions containing an osmotic stress agent, polyethylene glycol with molecular weight 8000 g/mol (PEG 8000)[23]. Osmotically suppressing DNA ejection from HSV-1, this work provides the first experimental evidence of a high internal pressure within a eukaryotic human virus

Results and Discussion

Conclusions

Materials and Methods