Conformation and activity of mannose- and N-acetylgalactosamine-specific lectins from Vicia villosa seeds

A review of Vicieae lectins studies: End of the book or a story in the writing?

Vicieae tribe, Leguminosae family (Fabaceae), has been extensively studied. In particular, the study of lectins. The purification, physicochemical and structural characterizations of the various purified lectins and the analysis of their relevant biological activities are ongoing. In this review, several works already published about Vicieae lectins are addressed. Initially, we presented the purification protocols and the physicochemical aspects, such as specificity for carbohydrates, optimal activity in the face of variations in temperature and pH, as well metals-dependence. Following, structural characterization studies are highlighted and, finally, various biological activities already reported are summarized. Studies on lectins in almost all genera (Lathyrus, Lens, Pisum and Vicia) are considered, with the exception of Vavilovia which studies of lectins have not yet been reported. Like other leguminous lectins, Vicieae lectins present heterogeneous profiles of agglutination profiles for erythrocytes and other cells of the immune system, and glycoproteins. Most Vicieae lectins consist of two subunits, α and β, products of a single precursor protein derived from a single gene. The differences between the isoforms result from varying degrees of proteolytic processing. Along with the identification of these molecules and their characteristics, biological activities become very relevant and robust for both basic and applied research.

Purification, Characterization, and Antiproliferative Activity of a Single-Chain Lectin from Vicia palaestina (Fabaceae) Seeds

Vicia palaestina Boiss. is an annual herb that grows in dry areas of eastern Mediterranean countries. It belongs to section Cracca subgenus Vicilla, which is characterized by having a high content in the non-protein amino acid canavanine. The seeds from some of these vetches are also rich in lectins. The purification and characterization of a single-chain lectin from the seeds of V. palaestina is described here. This lectin was the most abundant protein in albumin extracts. It has affinity for the glycoconjugate N-acetylgalactosamine and inhibits proliferation of the cancerous Caco-2 and THP-1 cell lines. In addition to their high nutritional value, the seeds from V. palaestina represent a source of lectins with health promoting and pharmacological potential because of their antiproliferative activity.

Mass spectrometry-based analyses showing the effects of secretor and blood group status on salivary N-glycosylation

Background

The carbohydrate portions of salivary glycoproteins play important roles, including mediating bacterial and leukocyte adhesion. Salivary glycosylation is complex. Many of its glycoproteins present ABO and Lewis blood group determinants. An individual’s genetic complement and secretor status govern the expression of blood group antigens. We queried the extent to which salivary glycosylation varies according to blood group and secretor status. First, we screened submandibular/sublingual and parotid salivas collected as ductal secretions for reactivity with a panel of 16 lectins. We selected three lectins that reacted with the largest number of glycoproteins and one that recognized uncommon lactosamine-containing structures. Ductal salivas representing a secretor with complex blood group expression and a nonsecretor with a simple pattern were separated by SDS-PAGE. Gel slices were trypsin digested and the glycopeptides were individually separated on each of the four lectins. The bound fractions were de-N-glycosylated. LC–MS/MS identified the original glycosylation sites, the peptide sequences, and the parent proteins.

Results

The results revealed novel salivary N-glycosites and glycoproteins not previously reported. As compared to the secretor, nonsecretor saliva had higher levels of N-glycosylation albeit with simpler structures.

Conclusions

Together, the results suggested a molecular basis for inter-individual variations in salivary protein glycosylation with functional implications for oral health.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9100-y) contains supplementary material, which is available to authorized users.

Sweetening the pot: adding glycosylation to the biomarker discovery equation

BACKGROUND

Cancer has profound effects on gene expression, including a cell's glycosylation machinery. Thus, tumors produce glycoproteins that carry oligosaccharides with structures that are markedly different from the same protein produced by a normal cell. A single protein can have many glycosylation sites that greatly amplify the signals they generate compared with their protein backbones.

CONTENT

In this article, we survey clinical tests that target carbohydrate modifications for diagnosing and treating cancer. We present the biological relevance of glycosylation to disease progression by highlighting the role these structures play in adhesion, signaling, and metastasis and then address current methodological approaches to biomarker discovery that capitalize on selectively capturing tumor-associated glycoforms to enrich and identify disease-related candidate analytes. Finally, we discuss emerging technologies--multiple reaction monitoring and lectin-antibody arrays--as potential tools for biomarker validation studies in pursuit of clinically useful tests.

SUMMARY

The future of carbohydrate-based biomarker studies has arrived. At all stages, from discovery through verification and deployment into clinics, glycosylation should be considered a primary readout or a way of increasing the sensitivity and specificity of protein-based analyses.

Structural and thermodynamic studies of KM+, a d-mannose binding lectin from Artocarpus integrifolia seeds

The KM+ lectin exhibits a novel and unusual circular dichroism (CD) spectrum that could be explained by a high proline content that would be inducing deformation of the beta-structure and/or unusual turns. KM+ was shown to be a very rigid lectin, which was very stable under a broad variety of conditions (urea, guanidine, hydrolysis, pH, etc.). Only incubation for 60 min at 333-338 K and extreme basic pH were able to induce conformational changes which could be observed by CD and fluorescence measurements. Data from CD are typical for protein denaturing associated with changes in the overall secondary structure. Data from high-performance size exclusion chromatography (SEC) showed that the denatured forms produced at pH 12.0 are eluted in clusters that co-elute with the native forms. A significant contribution from the tyrosines to the fluorescence emission upon denaturation was observed above 328 K. In fact at 328 K some broadening of the emission spectrum takes place followed by the appearance of a shoulder (approx. 305 nm) at 333 K and above. The sensitivity of tryptophan fluorescence to the addition of sugar suggests a close proximity of the tryptophan residues to the sugar binding site, K(a)=(2.9+/-0.6)x10(3) M(-1). The fraction of chromophore accessible to the quencher obtained is f(a)=0.43+/-0.08, suggesting that approximately 50% of the tryptophan residues are not accessible to quenching by d-mannose. KM+ thermal denaturation was found to be irreversible and was analyzed using a two-state model (N-->D). The results obtained for the activation energy and transition temperature from the equilibrium CD studies were: activation energy, E(a)=134+/-11 kJ/mol and transition temperature, T(m)=339+/-1 K, and from the fluorescence data: E(a)=179+/-18 kJ/mol and T(m)=337+/-1 K. Kinetic studies gave the following values: E(a)=108+/-18 kJ/mol and E(a)=167+/-12 kJ/mol for CD and fluorescence data, respectively.