The specificity of frutalin lectin using biomembrane models

On the role of surrounding regions in the fusion peptide in dengue virus infection

Dengue virus infection depends on its fusion with the host membrane, where the binding occurs through interaction between proteins on the virus cell surface and specific viral receptors on target membranes. This process is mediated by the fusion peptide located between residues 98 and 112 (DRGWGNGCGLFGKGG) that forms a loop in domain II of dengue E glycoprotein. In this study, we evaluated the role of fusion peptide surrounding regions (88-97 and 113-123) of the Dengue 2 subtype on its interaction with the membrane and fusion activity. These sequences are important to stabilize the fusion peptide loop and increase fusion activity. Three peptides, besides the fusion peptide, were synthesized by SPPS using the Fmoc chemical approach. The first contains the fusion peptide and the C-terminal region of the loop (sequence 98-123); another contains the N-terminal region (88-112) and the larger peptide contains both regions (88-123). The peptides were able to interact with a model membrane. Differences in morphology of the monolayer promoted by the peptides were assessed by Brewster Angle Microscopy (BAM). Our data indicated that the C-terminal region of fusion peptide loop is more efficient in promoting fusion and interacting with the membrane than the N-terminal sequence, which is responsible for the electrostatic initial interaction. We propose a 2-step mechanism for the interaction of the dengue virus fusion peptide with the host membrane, where the N-terminal sequence docks electrostatically on the headgroups and then the C-terminal interacts via hydrophobic forces in the acyl chains.

Label-Free Proteome Analysis of Plasma from Patients with Breast Cancer: Stage-Specific Protein Expression

Breast cancer is one of the most commonly diagnosed types of cancer among women. Breast cancer mortality rates remain high probably because its diagnosis is hampered by inaccurate detection methods. Since changes in protein expression as well as modifications in protein glycosylation have been frequently reported in cancer development, the aim of this work was to study the differential expression as well as modifications of glycosylation of proteins from plasma of women with breast cancer at different stages of disease (n = 30) compared to healthy women (n = 10). A proteomics approach was used that depleted albumin and IgG from plasma followed by glycoprotein enrichment using immobilized Moraceae lectin (frutalin)-affinity chromatography and data-independent label-free mass spectrometric analysis. Data are available via ProteomeXchange with identifier PXD003106. As result, 57,016 peptides and 4,175 proteins among all samples were identified. From this, 40 proteins present in unbound (PI—proteins that did not interact with lectin) and bound (PII—proteins that interacted with lectin) fractions were differentially expressed. High levels of apolipoprotein A-II were detected here that were elevated significantly in the early and advanced stages of the disease. Apolipoprotein C-III was detected in both fractions, and its level was increased slightly in the PI fraction of patients with early-stage breast cancer and expressed at higher levels in the PII fraction of patients with early and intermediate stages. Clusterin was present at higher levels in both fractions of patients with early and intermediate stages of breast cancer. Our findings reveal a correlation between alterations in protein glycosylation, lipid metabolism, and the progression of breast cancer.

Crystallization and preliminary X-ray diffraction studies of frutalin, an α-D-galactose-specific lectin from Artocarpus incisa seeds

Frutalin is an α-D-galactose-specific carbohydrate-binding glycoprotein with antitumour properties and is a powerful tool for tumour biomarker discovery. The crystallization and preliminary X-ray diffraction analysis of this lectin, which was isolated from Artocarpus incisa seeds, are reported here. Frutalin was purified and submitted to mass-spectrometric analysis. Diverse masses at approximately 16 kDa were observed in the deconvoluted spectra, which support the presence of isoforms. The best frutalin crystals were grown within a week in 0.1 M citric acid pH 3.5 which contained 25% PEG 3350 as a precipitant at 293 K, and diffracted to a maximum resolution of 1.81 Å. The monoclinic crystals belonged to space group I2, with unit-cell parameters a = 76.17, b = 74.56, c = 118.98 Å, β = 96.56°. A molecular-replacement solution was obtained which indicated the presence of four monomers per asymmetric unit. Crystallographic refinement of the structure is in progress.

Recombinant production of plant lectins in microbial systems for biomedical application - the frutalin case study

Frutalin is a homotetrameric partly glycosylated α-D-galactose-binding lectin of biomedical interest from Artocarpus incisa (breadfruit) seeds, belonging to the jacalin-related lectins family. As other plant lectins, frutalin is a heterogeneous mixture of several isoforms possibly with distinct biological activities. The main problem of using such lectins as biomedical tools is that "batch-to-batch" variation in isoforms content may lead to inconstant results. The production of lectins by recombinant means has the advantage of obtaining high amounts of proteins with defined amino-acid sequences and more precise properties. In this mini review, we provide the strategies followed to produce two different forms of frutalin in two different microbial systems: Escherichia coli and Pichia pastoris. The processing and functional properties of the recombinant frutalin obtained from these hosts are compared to those of frutalin extracted from breadfruit. Emphasis is given particularly to recombinant frutalin produced in P. pastoris, which showed a remarkable capacity as biomarker of human prostate cancer and as apoptosis-inducer of cancer cells. Recombinant frutalin production opens perspectives for its development as a new tool in human medicine.

Cytotoxic effects of native and recombinant frutalin, a plant galactose-binding lectin, on HeLa cervical cancer cells

Frutalin is the α-D-galactose-binding lectin isolated from breadfruit seeds. Frutalin was obtained from two different sources: native frutalin was purified from its natural origin, and recombinant frutalin was produced and purified from Pichia pastoris. This work aimed to study and compare the effect of native and recombinant frutalin on HeLa cervical cancer cells proliferation and apoptosis. Furthermore, the interaction between frutalin and the HeLa cells was investigated by confocal microscopy. Despite having different carbohydrate-binding affinities, native and recombinant frutalin showed an identical magnitude of cytotoxicity on HeLa cells growth (IC₅₀~100 μg/mL) and equally induced cell apoptosis. The interaction studies showed that both lectins were rapidly internalised and targeted to HeLa cell's nucleus. Altogether, these results indicate that frutalin action is not dependent on its sugar-binding properties. This study provides important information about the bioactivity of frutalin and contributes to the understanding of the plant lectins cytotoxic activity.