Structure of herpes simplex virus pUL7:pUL51, a conserved complex required for efficient herpesvirus assembly

Herpesviruses are an ancient family of highly-prevalent human and animal pathogens that acquire their membrane envelopes in the cytoplasm of infected cells. While multiple conserved viral proteins are known to be required for efficient herpesvirus production, many of these proteins lack identifiable structural homologues and the molecular details of herpesvirus assembly remain unclear. We have characterized the complex of assembly proteins pUL7 and pUL51 from herpes simplex virus (HSV)-1, an α-herpesvirus, using multi-angle light scattering and small-angle X-ray scattering with chemical crosslinking. HSV-1 pUL7 and pUL51 form a stable 1:2 complex that is capable of higher-order oligomerization in solution. We solved the crystal structure of this complex, revealing a core heterodimer comprising pUL7 bound to residues 41–125 of pUL51. While pUL7 adopts a previously-unseen compact fold, the extended helix-turn-helix conformation of pUL51 resembles the cellular endosomal complex required for transport (ESCRT)-III component CHMP4B, suggesting a direct role for pUL51 in promoting membrane scission during virus assembly. We demonstrate that the interaction between pUL7 and pUL51 homologues is conserved across human α-, β- and γ-herpesviruses, as is their association with -Golgi membranes in cultured cells. However, pUL7 and pUL51 homologues do not form complexes with their respective partners from different virus families, suggesting that the molecular details of the interaction interface have diverged. Our results demonstrate that the pUL7:pUL51 complex is conserved across the herpesviruses and provide a structural framework for understanding its role in herpesvirus assembly.