Viral Modulators of Herpesvirus Transport: Insights into Assembly and Transport RegulationPublic Deposited
Herpesviruses require axonal transport for the successful establishment of infection in peripheral ganglia (retrograde transport), and the subsequent spread to exposed body surfaces following reactivation from latency (anterograde transport). Viral progeny are assembled and spread to other tissues or hosts during egress. I focused on viral proteins which modulate directed transport and assembly of viral particles. Recent data from our lab shows fully that assembled viral particles (comprised of capsid, tegument layer, and envelope) are transported in a membrane bound vesicle to the axon terminal. Dissociation of the capsid from the membrane results in misdirection of the capsid back to the nucleus. Interactions between the different compartments of the viral particle are critical to assembly of infectious particles. I identified a novel and direct interaction between the tegument protein VP1/2 and the capsid associated protein UL25; both are essential to viral propagation. This interaction was identified through immunoprecipitation of transiently expressed proteins, fluorescence colocalization during infection, and viral nucleocapsid isolation. A capsid binding domain comprised of the 62-carboxy terminal amino acids of VP1/2 interacts with the capsid through UL25. The role of the viral kinases, US3 and UL13, during axonal transport in sensory neurons was examined by time-lapse fluorescence microscopy. Following replication of mutant viruses lacking kinase activity, viral progeny displayed an increase in retrograde motion that prevented efficient delivery to the distal axon. The aberrant increase in retrograde motion was accompanied by dissociation of the viral membrane from the transporting capsid, indicating that the viral kinases allow for efficient anterograde transport by stabilizing membrane-capsid interactions during the long transit from the neuron cell body to the distal axon. Together, these novel findings provide insight into how herpesvirus particles are assembled and transported to the axon terminal, where spread to other hosts may occur.