Exploration of carbohydrate binding behavior and anti-proliferative activities of Arisaema tortuosum lectin

Kshema Thakur,Tarnjeet Kaur,Rachna Hora,Manpreet Kaur,Jatinder Singh

doi:10.1186/s12867-019-0132-0

Abstract

BackgroundLectins have come a long way from being identified as proteins that agglutinate cells to promising therapeutic agents in modern medicine. Through their specific binding property, they have proven to be anti-cancer, anti-insect, anti-viral agents without affecting the non-target cells. The Arisaema tortuosum lectin (ATL) is a known anti-insect and anti-cancer candidate, also has interesting physical properties. In the present work, its carbohydrate binding behavior is investigated in detail, along with its anti-proliferative property.ResultsThe microcalorimetry of ATL with a complex glycoprotein asialofetuin demonstrated trivalency contributed by multiple binding sites and enthalpically driven spontaneous association. The complex sugar specificity of ATL towards multiple sugars was also demonstrated in glycan array analysis in which the trimannosyl pentasaccharide core N-glycan [Manα1-6(Manα1-3)Manβ1-4GlcNAcβ1-4GlcNAcβ] was the highest binding motif. The high binding glycans for ATL were high mannans, complex N-glycans, core fucosylated N-glycans and glycans with terminal lactosamine units attached to pentasaccharide core. ATL induced cell death in IMR-32 cells was observed as time dependent loss in cell number, formation of apoptotic bodies and DNA damage. As a first report of molecular cloning of ATL, the in silico analysis of its cDNA revealed ATL to be a β-sheet rich heterotetramer. A homology model of ATL showed beta prism architecture in each monomer with 85% residues in favoured region of Ramachandran plot.ConclusionsDetailed exploration of carbohydrate binding behavior indicated ATL specificity towards complex glycans, while no binding to simple sugars, including mannose. Sequence analysis of ATL cDNA revealed that during the tandem evolutionary events, domain duplication and mutations lead to the loss of mannose specificity, acquiring of new sugar specificity towards complex sugars. It also resulted in the formation of a two-domain single chain polypeptide with both domains having different binding sites due to mutations within the consensus carbohydrate recognition sites [QXDXNXVXY]. This unique sugar specificity can account for its significant biological properties. Overall finding of present work signifies anti-cancer, anti-insect and anti-viral potential of ATL making it an interesting molecule for future research and/or theragnostic applications.

Highlights

Lectins have come a long way from being identified as proteins that agglutinate cells to promising therapeutic agents in modern medicine
Lectin–carbohydrate interaction Isothermal titration microcalorimetry Various thermodynamic parameters characterizing ligand (Asialofetuin, Afet) binding of Arisaema tortuosum lectin (ATL) are provided in Additional file 1: Table S1
ATL–Afet binding demonstrates an exothermic reaction in which the heat released is a function of ATL–Afet molar ratio

Summary

Introduction

Lectins have come a long way from being identified as proteins that agglutinate cells to promising therapeutic agents in modern medicine. Through their specific binding property, they have proven to be anti-cancer, anti-insect, anti-viral agents without affecting the non-target cells. With a size large enough to be capable of generating immunogenic response, they are instead, becoming favourites in alternative therapies. This is due to their highly specific binding nature which remains central to their various activities. Lectins are known to bind directly to specific cells [10]

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Conclusion