The crystal structure of the varicella zoster Orf24-Orf27 nuclear egress complex spotlights multiple determinants of herpesvirus subfamily specificity

Varicella zoster virus (VZV) is a human pathogen from the α-subfamily of herpesviruses. Here, the crystal structure of the VZV Orf24-Orf27 complex is described, representing the essential viral core nuclear egress complex (NEC) that orchestrates the egress of the preassembled capsids from the nucleus. While previous studies have primarily emphasized the finding that the architecture of core NEC complexes is highly conserved among herpesviruses, the present report focusses on subfamily-specific structural and functional features that help explain the differences in the autologous versus nonautologous interaction patterns observed for NEC formation across herpesviruses. CoIP and confocal imaging data show that Orf24-Orf27 complex formation displays some promiscuity in a herpesvirus subfamily-restricted manner. At the same time, analysis of the NEC formation thermodynamic parameters of three prototypical α-, β- and γ herpesviruses, i.e. VZV, human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) reveals highly similar binding affinities for the autologous interaction with some specific differences in the enthalpy and entropy terms. Computational alanine scanning and structural comparisons highlight intermolecular interactions shared among α-herpesviruses that are clearly distinct from those seen in β- and γ-herpesviruses. Combined, these data allow to explain the distinct properties of specificity and permissivity so far observed in herpesviral NEC interactions. These findings might prove highly valuable when attempting to target multiple herpesvirus core NECs with selective or broad-acting drug candidates.