Mannosylated hemagglutinin peptides bind cyanovirin-N independent of disulfide-bonds in complementary binding sites

Cyanovirin-N (CV-N) has been shown to reveal broad neutralizing activity against human immunodeficiency virus (HIV) and to specifically bind Man alpha(1 -> 2)Man alpha units exposed on various glycoproteins of enveloped viruses, such as influenza hemagglutinin (HA) and Ebola glycoprotein. Chemically synthesized dimannosylated HA peptides bound domain-swapped and dimeric CV-N with either four disulfide-bonds (Cys-Cys), or three Cys-Cys bonds and an intact fold of the high-affinity binding site at an equilibrium dissociation constant K-D of 10 mu M. Cys-Cys mutagenesis with ion-pairing amino-acids glutamic acid and arginine was calculated by in silico structure-based protein design and allowed for recognizing dimannose and dimannosylated peptide binding to low-affinity binding sites (K-D approximate to 11 mu M for one C58-C73 bond, and binding to dimannosylated peptide). In comparison, binding to HA was achieved based on one ion-pairing C58E-C73R substitution at K-D = 275 nM, and K-D = 5 mu M for two C58E-C73R substitutions. We were utilizing a triazole bioisostere linkage to form the respective mannosylated-derivative on the HA peptide sequence of residues glutamine, glycine, and glutamic acid. Thus, mono- and dimannosylated peptides with N-terminal cysteine facilitated site-specific interactions with HA peptides, mimicking a naturally found N-linked glycosylation site on the HA head domain.