In Silico and in vitro evaluation of Cucurbitaceae seed lectins as promising prophylactic and therapeutic agents against SARS-CoV-2.

Concern over COVID-19 has arisen from continuous mutations in SARS-CoV-2 genome leading to emergence of novel variants. A detailed study and understanding of N-linked glycans (NAGs) of SARS-CoV-2 spike protein are key for the development of vaccines and new therapeutic strategies. Potential of four Cucurbitaceae seed lectins (CSLs) to inhibit SARS-CoV-2 attachment to host cells via interaction with receptor binding domain (RBD), was determined by Molecular Docking using PRODIGY and LZerD web servers. Among them, Luffa cylindrica lectin (PDB ID: 1NIO) displayed the most significant binding (B.E.: -24.9 kcal/mol; Kd: 0.052 aM). Further, docking (HADDOCK version 2.4) and interaction analysis (PDBsum and LigPlot+) of 1NIO with defined glycan site of SARS-CoV-2 spike protein revealed that glycans NAGs 1303, 1304, 1305, 1309 and 1314 on spike protein formed stable interactions with NAGs 248 and 249 on the lectin. Notably, NAG248 played a dual role in glycan-glycan interaction and binding. Momordia charantia seed lectin (MCSL) was partially purified using a combination of ethanol precipitation and affinity chromatography. Hemagglutination test confirmed antiviral activity and validated the utility of MCSL on human samples. Toxicity assessment of MCSL on normal HEK-293 cells using MTT assay revealed no significant effect on their morphology and viability at 10-100 µg/mL. Thus, CSLs have the potential to emerge as promising broad spectrum antiviral candidates against COVID-19 if investigated further. The present work is unique in that no such work is being done presently on anti-SARS-CoV-2 potential of CSLs. Also, very few in silico studies focusing on lectin-glycan interactions exist to date.