Intermolecular disulfide bond of PRRSV GP5 and M facilitates VLPs secretion and cell binding

Porcine reproductive and respiratory syndrome virus (PRRSV), the causative agent of porcine reproductive and respiratory syndrome (PRRS), continues to significantly impact on the global swine industry. GP5 and M are the primary structural proteins of PRRSV, playing crucial roles in the processes of virus attachment, entry, assembly and budding. The co-expression of GP5 and M can result in the formation of virus-like particles (VLPs). However, the underlying mechanisms remain incompletely understood. This study investigated the role of GP5-M interaction in VLPs secretion and cell binding. VLPs were generated by co-expressing GP5 and M via recombinant baculoviruses in Sf9 cells and confirmed by transmission electron microscopy. The secretion of VLPs was modulated by the expression levels of GP5 and M. Using the BirA technique, the GP5-M interaction was confirmed in Sf9 cells. Disruption of the N-terminally intermolecular disulfide bond between GP5 and M weakened, but did not completely abolish, the interaction between the proteins, leading to reduced VLPs secretion. Notably, the absence of this intermolecular disulfide bond resulted in the loss of VLPs' ability to bind to MARC-145 cells. In summary, our findings reveal the critical function of the intermolecular disulfide bond in GP5-M interaction, which significantly contributes to VLPs secretion and cell binding, and suggest potential interaction sites between GP5 and M.