| الوصف: |
Marek’s Disease Virus (MDV, Gallid alphaherpesvirus-2) is an oncogenic alphaherpesvirus that affects poultry and results in severe economic losses. The US3 kinase is conserved amongst alphaherpesviruses and facilitates several steps in viral replication, including viral budding from the nucleus and rearrangement of the host cytoskeleton. US3 from MDV remodels the actin cytoskeleton in a kinase-independent manner, the mechanism for which remains to be understood. Here, using proximity-dependent biotinylation and proteomic mass spectrometry, the actin-crosslinking protein alpha-actinin was identified as a new interactor of MDV US3. Using purified proteins, we demonstrate that US3 directly binds alpha-actinin in a Ca2+-dependent manner and blocks its actin-bundling activity in vitro. Ab initio protein structure prediction and molecular modelling suggest that the N-terminal 111 amino acids of US3 bind to the calponin-homology domains of alpha-actinin in their “closed” conformation, which is adopted in the presence of Ca2+ and incompatible with binding actin. Indeed, an ~7-fold increase in the affinity between MDV US3 and chicken alpha-actinin occurs in the presence of Ca2+ ions. Overexpression of alpha-actinin-4 counteracted the removal of stress fibres by kinase-dead, but not wild-type MDV US3. In addition to actinin, we also identified the microtubule motor dynein as an interactor of US3. Using fluorescent single-molecule motility assays, US3-GFP was observed being transported by both dynein and the kinesin KIF1C. This finding could have implications for the intracellular transport of the virus that needs to be further investigated. Together, these findings determine the mechanism for kinase-independent removal of stress fibres and identify new host interactors of MDV US3. |
