BanLec is a jacalin-related lectin isolated from the fruit of bananas, Musa acuminata. This lectin binds to high mannose carbohydrate structures, including those found on viruses containing glycosylated envelope proteins such as human immunodeficiency virus type-1 (HIV-1). Therefore, we hypothesized that BanLec might inhibit HIV-1 through binding of the glycosylated HIV-1 envelope protein, gp120. We determined that

Summary A key effector route of the Sugar Code involves lectins that exert crucial regulatory controls by targeting distinct cellular glycans. We demonstrate that a single amino acid substitution in a banana lectin, replacing histidine 84 with a threonine, significantly reduces its mitogenicity while preserving its broad-spectrum antiviral potency. X-ray crystallography, NMR spectroscopy, and glycocluster assays reveal that loss of mitogenicity is strongly correlated with loss of pi-pi stacking between aromatic amino acids H84 and Y83, which removes a wall separating two carbohydrate binding sites, thus diminishing multivalent interactions. On the other hand, monovalent interactions and antiviral activity are preserved by retaining other wild-type conformational features and possibly through unique contacts involving the T84 side chain. Through such fine-tuning, target selection and downstream effects of a lectin can be modulated so as to knock down one activity while preserving another, thus providing tools for therapeutics and for understanding the Sugar Code.

No abstract

A blood group B-specific lectin from the mushroom Marasmius oreades (MOA) was investigated with respect to its molecular structure and carbohydrate binding properties. SDS-PAGE mass spectrometric analysis showed it to consist of an intact (H; 33 kDa) and truncated (L; 23 kDa) subunit in addition to a small polypeptide (P; 10 kDa). Isolation in the presence of EDTA produced only the H subunits, indicating that the latter two are formed by metalloprotease cleavage of the intact H subunit. Tryptic digestion of the H, L, and P polypeptide chains followed by mass spectral analysis supports this view. The lectin strongly precipitated blood group type B substance, was nonreactive with type A substance, and reacted weakly with type H substance. Carbohydrate binding studies reveal a high affinity for Gal␣1,3Gal (but not for the isomeric ␣1,2-, ␣1,4-, and ␣1,6-disaccharides); Gal␣1,3Gal␤1,4GlcNAc; and the type B branched trisaccharide. MOA also reacts strongly with murine laminin from the Engelbreth-Holm-Swarm sarcoma and bovine thyroglobulin, both of which contain multiple Gal␣1,3Gal␤1,4GlcNAc end groups. This linear B trisaccharide is a component of porcine tissues and organs, preventing their transplantation into humans. MOA also shares carbohydrate recognition of this trisaccharide with toxin A elaborated by Clostridium difficile.Blood group-specific lectins have served as serological reagents for typing blood for over 65 years (1)(2)(3). Among the useful reagents are Dolichos biflorus lectin for human type A 1 erythrocytes (4, 5), the B 4 Griffonia simplicifolia isolectin for type B erythrocytes (6), and the Ulex europeus I (7, 8) and eel (Anguilla anguilla) serum agglutinins for type O(H) erythrocytes (1, 2). Of all the blood group-specific lectins studied, group B-specific lectins are probably fewest in number.Presently, the fruiting bodies of mushrooms are being studied as sources for lectins with novel carbohydrate binding activity. Several surveys have been published that classify these proteins based on their ability to agglutinate human (and rabbit) erythrocytes according to blood type (9 -12).Crude extracts of the mushroom Marasmius oreades (Tricholomataceae) were first reported to exhibit human type B erythrocyte agglutinating activity in 1951 (9, 13). A lectin from this source was isolated by affinity chromatography on a matrix of ␣-galactosyl-polyacrylamide gel by Horejsi and Kocourek (14). It was reported to agglutinate type B erythrocytes six times more avidly than type A erythrocytes and was stated to be a heterodimeric protein of 50 kDa, with subunits of 33 and 23 kDa. No mono-or oligosaccharides (25 mM) tested were found to inhibit agglutination of human type B erythrocytes.We have undertaken a more detailed investigation of this potentially important B-specific lectin with interesting results. Quantitative precipitation studies using a highly purified preparation with A, B, and O(H) blood group substances show absolute specificity for B versus A substance, with slight Obinding activity. Binding stud...

No abstract