Structural and Functional Characterisation of Novel Lectins from Underutilised Nigerian Legumes with Anticancer and Immunomodulatory Properties

Lectins are carbohydrate-binding proteins with diverse biological activities including anticancer and immunomodulatory properties, and underutilised Nigerian legumes represent a largely unexplored source of structurally novel lectins that may possess unique bioactivity profiles. This dissertation structurally and functionally characterises lectins isolated from three underutilised Nigerian legumes: Mucuna pruriens, Canavalia ensiformis (jack bean), and Pentaclethra macrophylla, sourced from the South East and South South zones. Lectins were isolated from seed extracts by affinity chromatography on Sephadex G-100 and carbohydrate-conjugated agarose columns, and purified to homogeneity. Structural characterisation employed SDS-PAGE, native PAGE, size exclusion chromatography, isoelectric focusing, circular dichroism spectroscopy, and primary sequence determination by tandem mass spectrometry combined with de novo sequencing. Haemagglutination activity, carbohydrate specificity, metal ion dependence, and pH-temperature stability profiles were determined. Functional characterisation of anticancer activity was assessed in MCF-7 breast cancer, HepG2 hepatocellular carcinoma, and HCT116 colon cancer cell lines by MTT assay, flow cytometric apoptosis analysis, and cell cycle analysis. Immunomodulatory activity was assessed by lymphocyte proliferation assay, cytokine induction profiling, and macrophage activation assays. The Mucuna pruriens lectin showed selective cytotoxicity against MCF-7 cells with IC50 of 18.4 micrograms per millilitre and induced apoptosis through the intrinsic mitochondrial pathway confirmed by caspase-9 activation and cytochrome c release. Pentaclethra macrophylla lectin showed potent macrophage activation and IL-12 induction, suggesting Th1 immunomodulatory potential. The dissertation makes original contributions to Nigerian legume lectin biochemistry and to structure-activity relationships of plant lectins in cancer biology. Keywords: lectins, Nigerian legumes, anticancer activity, immunomodulation, structural characterisation.