Isolation and Characterization of a Mannan-Binding Lectin from the Freshwater Cyanobacterium (Blue-Green Algae) Microcystis viridis

107

138

The primary structure of a lectin, designated Oscillatoria agardhii agglutinin (OAA), isolated from the freshwater cyanobacterium O. agardhii NIES-204 was determined by the combination of Edman degradation and electron spray ionizationmass spectrometry. OAA is a polypeptide (M r 13,925) consisting of two tandem repeats. Interestingly, each repeat sequence of OAA showed a high degree of similarity to those of a myxobacterium, Myxococcus xanthus hemagglutinin, and a marine red alga Eucheuma serra lectin. A systematic binding assay with pyridylaminated oligosaccharides revealed that OAA exclusively binds to high mannose (HM)-type N-glycans but not to other N-glycans, including complex types, hybrid types, and the pentasaccharide core or oligosaccharides from glycolipids. OAA did not interact with any of free mono-and oligomannoses that are constituents of the branched oligomannosides. These results suggest that the core disaccharide, GlcNAc-GlcNAc, is also essential for binding to OAA. The binding activity of OAA to HM type N-glycans was dramatically decreased when ␣1-2 Man was attached to ␣1-3 Man branched from the ␣1-6 Man of the pentasaccharide core. This specificity of OAA for HM-type oligosaccharides is distinct from other HM-binding lectins. Kinetic analysis with an HM heptasaccharide revealed that OAA possesses two carbohydrate binding sites per molecule, with an association constant of 2.41؋10 8 M ؊1 . Furthermore, OAA potently inhibits human immunodeficiency virus replication in MT-4 cells (EC 50 ‫؍‬ 44.5 nM). Thus, we have found a novel lectin family sharing similar structure and carbohydrate binding specificity among bacteria, cyanobacteria, and marine algae.

Section: Discussioncontrasting

confidence: 56%

Primary Structure and Carbohydrate Binding Specificity of a Potent Anti-HIV Lectin Isolated from the Filamentous Cyanobacterium Oscillatoria agardhii

Sato¹,

Okuyama

Hori

2007

107

138

“…Various lectins, including cyanovirin-N (6), DC-SIGN (7), scytovirin (8), griffithsin (9), MVL (10), and actinohivin (11), are known to bind to the high mannose glycans on gp120, thereby exerting anti-HIV activity. Interestingly, the binding modes and target epitopes on Man-9 are quite distinct for the different lectins.…”

mentioning

confidence: 99%

Novel Fold and Carbohydrate Specificity of the Potent Anti-HIV Cyanobacterial Lectin from Oscillatoria agardhii

Koharudin

Furey

Gronenborn

2011

Oscillatoria agardhii agglutinin (OAA) is a recently discovered cyanobacterial lectin that exhibits potent anti-HIV activity. Up to now, only its primary structure and carbohydrate binding data have been available. To elucidate the structural basis for the antiviral mechanism of OAA, we determined the structure of this lectin by x-ray crystallography at 1.2 Å resolution and mapped the specific carbohydrate recognition sites of OAA by NMR spectroscopy. The overall architecture of OAA comprises 10 ␤-strands that fold into a single, compact, ␤-barrel-like domain, creating a unique topology compared with all known protein structures in the Protein Data Bank. OAA sugar binding was tested against Man-9 and various disaccharide components of Man-9. Two symmetric carbohydratebinding sites were located on the protein, and a preference for Man␣(1-6)Man-linked sugars was found. Altogether, our structural results explain the antiviral activity OAA and add to the growing body of knowledge about antiviral lectins.HIV infection occurs via virus-cell and cell-cell fusion mediated by the two viral envelope glycoproteins gp120 and gp41 (1-3). gp120 interacts with the CD4 receptor of the host cell, resulting in a conformational change in gp120 that eventually leads to the insertion of the fusion peptide of gp41 into the target membrane, causing membrane fusion (4). The gp120 glycoprotein is remarkably enriched in high mannose N-linked sugars (5), and novel avenues for controlling HIV infection may become available by targeting to the sugars of gp120.Various lectins, including cyanovirin-N (6), DC-SIGN (7), scytovirin (8), griffithsin (9), MVL (10), and actinohivin (11), are known to bind to the high mannose glycans on gp120, thereby exerting anti-HIV activity. Interestingly, the binding modes and target epitopes on Man-9 are quite distinct for the different lectins. Cyanovirin-N specifically recognizes Man␣(1-2)Man-linked mannose substructures, in particular the D1 and D3 arms of Man-9 (12, 13); DC-SIGN preferentially interacts with the Man␣(1-3)Man␣(1-6)Man trisaccharide (14); griffithsin binds to single mannose units (15); and MVL specifically interacts with the Man␣(1-6)Man␤(1-4)GlcNAc␤(1-4)GlcNAc tetrasaccharide (16). Although no crystal structures for protein-carbohydrate complexes are available for scytovirin and actinohivin, sugar binding studies revealed specificities for Man␣(1-2)Man␣(1-6)Man␣(1-6)Man (17) and Man␣(1-2)Man (18), respectively.Here, we determined the crystal structure of Oscillatoria agardhii agglutinin (OAA), 2 a recently discovered cyanobacterial lectin with potent anti-HIV activity (19); mapped the carbohydrate-binding sites on the protein by NMR spectroscopy; and determined its oligosaccharide specificity. Our results demonstrate that OAA is unique with respect to both its structure and specific carbohydrate binding. Altogether, this work provides the molecular basis for understanding the potent anti-HIV activity of OAA and may aid in its further development as a useful diagnostic and pharmacological re...

“…Apart from the plant lectins, high mannose-binding cyanobacterial (blue-green algal) or eukaryotic algal lectins are a group of promising compounds for antiviral agents because of their unique oligosaccharide binding nature and physicochemical characteristics (6,7). For example, 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.…”

mentioning

confidence: 99%

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

Sato

Hirayama

Morimoto

et al. 2011

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 carbohydratebinding 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 ␣1-2-linked mannose at the nonreducing terminus. The binding activity was enhanced as the number of terminal ␣1-2-linked mannose substitutions increased. Mannobiose, mannotriose, and mannopentaose were incapable of binding to BCA. Thus, BCA preferentially recognized the nonreducing terminal ␣1-2-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.