Deciphering the packaging mechanism of the herpesvirus HSV-1

• Applicant: Dr. Laura Meißner
• Subject Area: Virology ; Biophysics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561072518

Herpesviruses are widespread in humans and once infected, the virus becomes latent and stays in the host. While herpesvirus infection is often mild in healthy individuals, infection or reactivation can lead to severe consequences in immunocompromised individuals. The Herpes simplex virus (HSV-1) causes cold sores and viral encephalitis. Kaposi’s sarcoma-associated herpesvirus and Epstein-Barr virus cause cancer. While many small molecules exist to help treat infections, available drugs exhibit nephrotoxicity. Additionally, drugs eventually become ineffective as resistance mutations develop in the population. Thus, discovery and development of new anti-herpesviral drugs is essential to help treat these human pathogens. To generate progeny viruses, the virus must package the genetic material into its capsid. Viral packaging is an attractive target for therapeutics, as viruses encode their own packaging machinery. Herpesviruses use a terminase motor to package their DNA genome into a pre-formed capsid. Additionally, an accessory factor of unknown function, UL32, is required for packaging, although both complexes do not stably interact. Surprisingly, the mechanism of viral genome packaging is conserved between herpesviruses and the tailed bacteriophages, but differs for example in the oligomeric state of the terminase and the accessory factor. While the packaging mechanism of bacteriophages is well-characterized, the biophysical mechanism of viral genome packaging in herpesviruses remains poorly understood. My first goal is to determine how the central components of the packaging machinery, the terminase and UL32, interact together and with DNA. My second aim is to reconstitute packaging in vitro using recombinantly expressed packaging components. Using TIRF microscopy, I will characterize the biophysical characteristics of the packaging process, e.g., velocity and pause frequency as well as the role of individual components. In the third aim, I will use optical tweezers to resolve individual packaging steps and measure the forces that the terminase produces in packaging. Using the outlined approaches, I will reconstitute the first packaging assay of a eukaryotic virus, HSV-1. I will determine the mechanistic contributions of each packaging factor and measure the dynamics of viral DNA translocation into the capsid. I anticipate that the results of the project will contribute to our understanding of the viral life cycle and the packaging process. These insights will pave the way to drug development targeting the function or interaction of packaging components.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Host: Allison Didychuk, Ph.D.