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

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.