Plant or microbial
lectins are known to exhibit potent
antiviral activities against viruses with glycosylated
surface proteins, yet the mechanism(s) by which these
carbohydrate-
binding proteins exert their
antiviral activities is not fully understood. Hepatitis C virus (HCV) is known to possess glycosylated envelope
proteins (gpE1E2) and to be potently inhibited by
lectins. Here, we tested in detail the
antiviral properties of the newly discovered Microcystis viridis
lectin (MVL) along with
cyanovirin-N (CV-N) and
Galanthus nivalis agglutinin (GNA) against cell culture HCV, as well as their binding properties toward viral particles, target cells, and recombinant HCV
glycoproteins. Using infectivity assays, CV-N, MVL, and GNA inhibited HCV with IC50 values of 0.6 nM, 30.4 nM, and 11.1 nM, respectively. Biolayer interferometry analysis demonstrated a higher affinity of GNA to immobilized recombinant HCV
glycoproteins compared to CV-N and MVL. Complementary studies, including fluorescence-activated cell sorting (FACS) analysis, confocal microscopy, and pre- and post-virus binding assays, showed a complex mechanism of inhibition for CV-N and MVL that includes both viral and cell association, while GNA functions by binding directly to the viral particle. Combinations of GNA with CV-N or MVL in HCV
infection studies revealed synergistic inhibitory effects, which can be explained by different
glycan recognition profiles of the mainly high-
mannoside specific
lectins, and supports the hypothesis that these
lectins inhibit through different and complex modes of action. Our findings provide important insights into the mechanisms by which
lectins inhibit HCV
infection. Overall, the data suggest MVL and CV-N have the potential for toxicity due to interactions with cellular
proteins while GNA may be a better therapeutic agent due to specificity for the HCV gpE1E2.