Griffithsin-mediated inhibition of cellular entry of hemorrhagic fever viruses and insights into its mechanisms.

UNLABELLED: Griffithsin (GRFT), a lectin derived from the red algae Griffithsia, is known as an antiviral agent that binds to high-mannose glycans on viral envelope glycoproteins (GPs). In this study, we evaluated the antiviral activity of GRFT against Ebola virus (EBOV), Marburg virus (MARV), Lassa virus (LASV), Lujo virus (LUJV), and Crimean-Congo hemorrhagic fever virus (CCHFV), all of which cause severe and often fatal hemorrhagic fevers in humans. GRFT effectively blocked the entry of these viruses into cells, with stronger inhibition observed against LASV, LUJV, and CCHFV than against EBOV and MARV. This inhibitory effect depended on the lectin activity of GRFT, as its mutant lacking glycan-binding function completely lost the ability to inhibit the entry of these viruses into cells. We found that GRFT induced aggregation of virus-like particles (VLPs) derived from EBOV and MARV, whereas this activity was not observed with LASV- and LUJV-derived VLPs. Most of the escape mutants of LASV and LUJV GPs exhibited amino acid substitutions that likely disrupted GRFT binding by removing glycosylation sites at positions 79 and 73, respectively. Interestingly, other substitutions close to these positions, although unrelated to glycosylation, also contributed to reduced inhibitory activity of GRFT, suggesting a unique recognition mode in which both sugar chains and adjacent amino acid residues constitute the binding site structure for GRFT. Overall, our results provide insights into mechanisms underlying the antiviral effects of GRFT and highlight lectin-related activities as a key feature for broad-spectrum antiviral agents targeting highly glycosylated envelope GPs.

IMPORTANCE: Emerging and re-emerging infectious diseases, including viral hemorrhagic fevers, pose a major global health threat due to their potential for widespread outbreaks. Currently, treatment options for such diseases are limited and often ineffective against newly emerging viruses. Here, we demonstrate that Griffithsin (GRFT), a naturally derived lectin from red algae, inhibits the entry of multiple hemorrhagic fever viruses into host cells. By blocking key processes of the viral entry mediated by envelope glycoproteins, lectins such as GRFT can exhibit broad antiviral activity that could potentially overcome the limitations of existing treatments against emerging viruses. Our findings emphasize that targeting sugar chains and adjacent structures on viral glycoproteins with GRFT could provide a therapeutic strategy against diverse viral species. Such an approach is particularly valuable for newly emerging viruses for which specific countermeasures have not yet been established.