High Mannose-binding Lectin with Preference for the Cluster of α1–2-Mannose from the Green Alga Boodlea coacta Is a Potent Entry Inhibitor of HIV-1 and Influenza Viruses

Yuichiro Sato,Makoto Hirayama,Kinjiro Morimoto,Naoki Yamamoto,Satomi Okuyama,Kanji Hori

doi:10.1074/jbc.m110.216655

Abstract

The complete amino acid sequence of a lectin from the green alga Boodlea coacta (BCA), which was determined by a combination of Edman degradation of its peptide fragments and cDNA cloning, revealed the following: 1) B. coacta used a noncanonical genetic code (where TAA and TAG codons encode glutamine rather than a translation termination), and 2) BCA consisted of three internal tandem-repeated domains, each of which contains the sequence motif similar to the carbohydrate-binding site of Galanthus nivalis agglutinin-related lectins. Carbohydrate binding specificity of BCA was examined by a centrifugal ultrafiltration-HPLC assay using 42 pyridylaminated oligosaccharides. BCA bound to high mannose-type N-glycans but not to the complex-type, hybrid-type core structure of N-glycans or oligosaccharides from glycolipids. This lectin had exclusive specificity for α1-2-linked mannose at the nonreducing terminus. The binding activity was enhanced as the number of terminal α1-2-linked mannose substitutions increased. Mannobiose, mannotriose, and mannopentaose were incapable of binding to BCA. Thus, BCA preferentially recognized the nonreducing terminal α1-2-mannose cluster as a primary target. As predicted from carbohydrate-binding propensity, this lectin inhibited the HIV-1 entry into the host cells at a half-maximal effective concentration of 8.2 nm. A high association constant (3.71 × 10(8) M(-1)) of BCA with the HIV envelope glycoprotein gp120 was demonstrated by surface plasmon resonance analysis. Moreover, BCA showed the potent anti-influenza activity by directly binding to viral envelope hemagglutinin against various strains, including a clinical isolate of pandemic H1N1-2009 virus, revealing its potential as an antiviral reagent.

Highlights

IntroductionFrom Japan Society of the Promotion of Science. □S The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2 and Tables 1 and 2
From Japan Society of the Promotion of Science. □S The on-line version of this article contains supplemental Figs. 1 and 2 and Tables 1 and 2
Purification of BCA—The lectin of B. coacta was extracted with buffer and effectively recovered as a precipitate with 75% saturated ammonium sulfate

Summary

Introduction

From Japan Society of the Promotion of Science. □S The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2 and Tables 1 and 2. HIV-inactivating proteins such as CV-N from Nostoc ellipsosporum [8, 9], scytovirin from Scytonema varium [10], MVL from Microcystis viridis [11], and OAA from Oscillatoria agardhii [12] are high mannose-binding cyanobacterial lectins These prokaryotic lectins share the common structural features, an internal multiplication of the amino acid sequences. Red algal lectin ESA-2 from Eucheuma serra is structurally and evolutionarily related to the cyanobacterial lectin OAA [15] Both lectins exclusively recognize high mannose-type N-glycans with extremely high affinity (association constant (KA) ϭ ϳ108 MϪ1) but do not recognize monosaccharides or small oligomannoses [12, 15]. Detailed oligosaccharide binding specificity of BCA and its antiviral activity against two global viruses, HIV and influenza virus, were evaluated

Methods

Results

Conclusion