Tethered release of the pseudorabies virus deubiquitinase from the capsid promotes enzymatic activity

Herpesviruses carry an assortment of proteins in the interstitial space between the capsid and membrane envelope, collectively referred to as the tegument. Upon virion fusion with a cell, envelope integrity is disrupted, and many tegument constituents disperse into the cytosol to carry out individual effector functions, while others direct transport of the capsid to the nucleus. To gain insight into the tegument dynamics that occur with disruption of envelope integrity, we used a combination of single-particle fluorescence and biochemical approaches that leveraged the previously established use of n-ethylmaleimide to inhibit virion dynamics. We document that the large tegument protein (pUL36), which is stably bound to the capsid surface at its C-terminus, is also conditionally bound to the capsid via its N-terminal deubiquitinase (DUB) domain. The DUB is released, while remaining tethered to the capsid by the pUL36 C-terminus, by a mechanism dependent on reactive cysteines. Mutation of these cysteines locks the DUB in a capsid bound state and suppresses enzymatic activity.

Neuroinvasive alphaherpesviruses, such as herpes simplex virus and pseudorabies virus, cause a broad range of diseases in humans and other animals. Novel strategies to interfere with the virion structural rearrangements required for infectivity could prove valuable to treat infections, yet critical aspects of the virion architecture and its metastability remain poorly defined. In this study, we document that the pUL36 tegument protein exhibits conditional capsid binding in its N-terminal deubiquitinase domain that regulates enzymatic activity during infection.