Sequence studies of peanut agglutinin

A galactoside-specific Dalbergieae legume lectin from seeds of Vataireopsis araroba (Aguiar) Ducke

The Dalbergieae lectin group encompasses several lectins with significant differences in their carbohydrate specificities and biological properties. The current work reports on the purification and characterization of a GalNAc/Gal-specific lectin from Vataireopsis araroba (Aguiar) Ducke, designated as VaL. The lectin was purified from the seeds in a single step using guar gum affinity chromatography. The lectin migrated as a single band of about 35 kDa on SDS-PAGE and, in native conditions, occurs as a homodimer. The purified lectin is stable at temperatures up to 60 °C and in a pH range from 7 to 8 and requires divalent cations for its activity. Sugar-inhibition assays demonstrate the lectin specificity towards N-acetyl-D-galactosamine, D-galactose and related sugars. Furthermore, glycan array analyses show that VaL interacts preferentially with glycans containing terminal GalNAc/Galβ1-4GlcNAc. Biological activity assays were performed using three insect cell lines: CF1 midgut cells from the spruce budworm Choristoneura fumiferana, S2 embryo cells from the fruit fly Drosophila melanogaster, and GutAW midgut cells from the corn earworm Helicoverpa zea. In vitro assays indicated a biostatic effect for VaL on CF1 cells, but not on S2 and GutAW cells. The lectin presented a biostatic effect by reducing the cell growth and inducing cell agglutination, suggesting an interaction with glycans on the cell surface. VaL has been characterized as a galactoside-specific lectin of the Dalbergieae tribe, with sequence similarity to lectins from Vatairea and Arachis.

Dalbergieae lectins: A review of lectins from species of a primitive Papilionoideae (leguminous) tribe

Lectins are (glyco)proteins capable of reversibly binding to specific carbohydrates, thus having various functions and applications. Plant lectins are the best studied, and the Leguminoseae family is highlighted in a number of published works, especially species of the Papilionoideae subfamily. Dalbergieae is one of the tribes in this subfamily comprising 49 genera and over 1300 species. From this tribe, about 26 lectins were studied, among which we can highlight the Arachis hypogaea lectin, widely used in cancer studies. Dalbergieae lectins demonstrate various carbohydrate specificities and biological activities including anti-inflammatory, vasorelaxant, nociceptive, antibacterial, antiviral among others. Structurally, these lectins are quite similar in their three-dimensional folding but present significant differences in oligomerization patterns and in the conservation of carbohydrate-recognition domain. Despite the existence of structural data from some lectins, only sparse literature has reported on this tribe's diversity, not to mention the range of biological effects, determined through specific assays. Therefore, this work will review the most important studies on Dalbergieae lectins and their potential biomedical applications.

Cloning, sequence analysis and expression in Escherichia coli of the cDNA encoding a precursor of peanut agglutinin

The cDNA coding for pre-peanut agglutinin (PNA) was isolated from a bacterial expression library. It codes for a polypeptide of 273 amino acids composed of a hydrophobic signal peptide of 23 amino acids and a mature protein of 250 amino acids. The sequence of the latter is identical to that of native PNA, determined very recently by conventional methods, except that it contains 14 additional amino acids at the C-terminus. Bacterial cells harboring a plasmid with the prePNA-cDNA, produced two PNA cross-reacting proteins: one migrated on SDS-PAGE identically with the native lectin (apparent mol. wt. 31 kDa); the other, at 35 kDa, was a beta-galactosidase pre-PNA fusion protein. The former protein possessed an N-terminal sequence identical to that of the mature, native PNA, suggesting that it was processed from the 35 kDa prePNA precursor. Only the 31 kDa protein was exported into the bacterial periplasmic space, and had the ability to bind to galactose-Sepharose. The isolated processed protein had the same hemagglutinating activity as the native lectin, when assayed with sialidase-treated human erythrocytes. Like the native lectin, it did not agglutinate the untreated cells, was not inhibited by N-acetylgalactosamine, and was inhibited by Gal beta 1----3GalNAc 30-times more strongly than by galactose.

The amino acid sequence of peanut agglutinin

The amino acid sequence of peanut (Arachis hypogaea) agglutinin was determined from three major fragments obtained by mild acid cleavage at Asp-Pro peptide bonds. The sequence of 236 amino acids has residues identical to those that form the metal-binding site and the hydrophobic pocket in concanavalin A and other lectins, although the overall similarity is only 42%. In the segments of peanut agglutinin that correspond to the four loops that form the carbohydrate-binding site in concanavalin A and favin, several central residues are homologous, while others show changes to smaller side chains, such as Tyr----Gly. The carbohydrate-binding site of peanut agglutinin may therefore have a similar peptide-backbone architecture, but form a considerably more open cleft.

The amino acid sequence of Erythrina corallodendron lectin and its homology with other legume lectins

The primary sequence of Erythrina corallodendron lectin was deduced from analysis of the peptides derived from the lectin by digestion with trypsin, chymotrypsin, Staphylococcus aureus V8 protease, elastase and lysylendopeptidase-C, and of fragments generated by cleavage of the lectin with dilute formic acid in 6 M guanidine hydrochloride. Purification of the individual peptides was achieved by gel filtration, followed by reverse phase HPLC. The glycosylation site (Asn17-Leu18-Thr19) was deduced from analysis of the glycopeptide isolated from a pronase digest of the lectin before and after deglycosylation of the glycopeptide with endoglycosidase F. Comparison of the sequence of 244 residues thus obtained with those of 9 other legume lectins revealed extensive homologies, including 39 invariant positions and 60 partial identities. These data provide further evidence for the conservation of the lectin gene in leguminous plants.

Evidence for the involvement of protein-carbohydrate interaction in hematopoietic, multipotential colony-stimulating factor-dependent stem cell proliferation

Immunologically important mediators have been shown to exhibit ability to specifically bind distinct carbohydrates. This type of protein-carbohydrate interaction is one mechanism how to explain involvement of glycochemical interactions in regulatory processes. Interference of certain saccharides with murine multipotential colony-stimulating factor (multi-CSF)-dependent colony formation from progenitor cells in semisolid agar raised evidence for similar potential involvement of protein-carbohydrate interactions. Affinity depletion of conditioned WEHI-3B-medium on resins, bearing saccharides that have been elucidated to be effective inhibitors (mannose and lactose), resulted in preparations with significantly reduced capability to sustain development and proliferation. Sequence comparison of multi-CSF to carbohydrate-binding proteins (lectins) with this specificity failed to uncover extended homologies in diagonal plots. But detailed sequence alignments revealed confined, high-scoring stretches of homology between various lectins and two types of CSF. These results prove the importance of protein-carbohydrate interactions in stem cell proliferation.