Functional Diversity of Novel Lectins with Unique Structural Features in Marine Animals

Carbohydrate-Binding Properties and Antimicrobial and Anticancer Potential of a New Lectin from the Phloem Sap of Cucurbita pepo

A Cucurbita phloem exudate lectin (CPL) from summer squash (Cucurbita pepo) fruits was isolated and its sugar-binding properties and biological activities were studied. The lectin was purified by affinity chromatography and the hemagglutination assay method was used to determine its pH, heat stability, metal-dependency and sugar specificity. Antimicrobial and anticancer activities were also studied by disc diffusion assays and in vivo and in vitro methods. The molecular weight of CPL was 30 ± 1 KDa and it was stable at different pH (5.0 to 9.0) and temperatures (30 to 60 °C). CPL recovered its hemagglutination activity in the presence of Ca2+. 4-nitrophenyl-α-D-glucopyranoside, lactose, rhamnose and N-acetyl-D-glucosamine strongly inhibited the activity. With an LC50 value of 265 µg/mL, CPL was moderately toxic and exhibited bacteriostatic, bactericidal and antibiofilm activities against different pathogenic bacteria. It also exhibited marked antifungal activity against Aspergillus niger and agglutinated A. flavus spores. In vivo antiproliferative activity against Ehrlich ascites carcinoma (EAC) cells in Swiss albino mice was observed when CPL exerted 36.44% and 66.66% growth inhibition at doses of 3.0 mg/kg/day and 6.0 mg/kg/day, respectively. A 12-day treatment by CPL could reverse their RBC and WBC counts as well as restore the hemoglobin percentage to normal levels. The MTT assay of CPL performed against human breast (MCF-7) and lung (A-549) cancer cell lines showed 29.53% and 18.30% of inhibitory activity at concentrations of 128 and 256 µg/mL, respectively.

A Novel Hemocyte-Derived Peptide and Its Possible Roles in Immune Response of Ciona intestinalis Type A

A wide variety of bioactive peptides have been identified in the central nervous system and several peripheral tissues in the ascidian Ciona intestinalis type A (Ciona robusta). However, hemocyte endocrine peptides have yet to be explored. Here, we report a novel 14-amino-acid peptide, CiEMa, that is predominant in the granular hemocytes and unilocular refractile granulocytes of Ciona. RNA-seq and qRT-PCR revealed the high CiEma expression in the adult pharynx and stomach. Immunohistochemistry further revealed the highly concentrated CiEMa in the hemolymph of the pharynx and epithelial cells of the stomach, suggesting biological roles in the immune response. Notably, bacterial lipopolysaccharide stimulation of isolated hemocytes for 1-4 h resulted in 1.9- to 2.4-fold increased CiEMa secretion. Furthermore, CiEMa-stimulated pharynx exhibited mRNA upregulation of the growth factor (Fgf3/7/10/22), vanadium binding proteins (CiVanabin1 and CiVanabin3), and forkhead and homeobox transcription factors (Foxl2, Hox3, and Dbx) but not antimicrobial peptides (CrPap-a and CrMam-a) or immune-related genes (Tgfbtun3, Tnfa, and Il17-2). Collectively, these results suggest that CiEMa plays roles in signal transduction involving tissue development or repair in the immune response, rather than in the direct regulation of immune response genes. The present study identified a novel Ciona hemocyte peptide, CiEMa, which paves the way for research on the biological roles of hemocyte peptides in chordates.

New l-Rhamnose-Binding Lectin from the Bivalve Glycymeris yessoensis: Purification, Partial Structural Characterization and Antibacterial Activity

In this study, a new l-rhamnose-binding lectin (GYL-R) from the hemolymph of bivalve Glycymeris yessoensis was purified using affinity and ion-exchange chromatography and functionally characterized. Lectin antimicrobial activity was examined in different ways. The lectin was inhibited by saccharides possessing the same configuration of hydroxyl groups at C-2 and C-4, such as l-rhamnose, d-galactose, lactose, l-arabinose and raffinose. Using the glycan microarray approach, natural carbohydrate ligands were established for GYL-R as l-Rha and glycans containing the α-Gal residue in the terminal position. The GYL-R molecular mass determined by MALDI-TOF mass spectrometry was 30,415 Da. The hemagglutination activity of the lectin was not affected by metal ions. The lectin was stable up to 75 °C and between pH 4.0 and 12.0. The amino acid sequence of the five GYL-R segments was obtained with nano-ESI MS/MS and contained both YGR and DPC-peptide motifs which are conserved in most of the l-rhamnose-binding lectin carbohydrate recognition domains. Circular dichroism confirmed that GYL is a α/β-protein with a predominance of the random coil. Furthermore, GYL-R was able to bind and suppress the growth of the Gram-negative bacteria E. coli by recognizing lipopolysaccharides. Together, these results suggest that GYL-R is a new member of the RBL family which participates in the self-defense mechanism against bacteria and pathogens with a distinct carbohydrate-binding specificity.