Elucidation of the interactions between SARS-CoV-2 Spike protein and wild and mutant types of IFITM proteins by in silico methods

COVID-19 is a viral disease that has been a threat to the whole world since 2019. Although effective vaccines against the disease have been developed, there are still points to be clarified about the mechanism of SARS-CoV-2, which is the causative agent of COVID-19. In this study, we determined the binding energies and the bond types of complexes formed by open (6VYB) and closed (6VXX) forms of the Spike protein of SARS-CoV-2 and wild and mutant forms of IFITM1, IFITM2, and IFITM3 proteins using the molecular docking approach. First, all missense SNPs were found in the NCBI Single Nucleotide Polymorphism database (dbSNP) for IFITM1, IFITM2, and IFITM3 and analyzed with SIFT, PROVEAN, PolyPhen-2, SNAP2, Mutation Assessor, and PANTHER cSNP web-based tools to determine their pathogenicity. When at least four of these analysis tools showed that the SNP had a pathogenic effect on the protein product, this SNP was saved for further analysis. Delta delta G (DDG) and protein stability analysis for amino acid changes were performed in the web-based tools I-Mutant, MUpro, and SAAFEC-SEQ. The structural effect of amino acid change on the protein product was made using the HOPE web-based tool. HawkDock server was used for molecular docking and Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) analysis and binding energies of all complexes were calculated. BIOVIA Discovery Studio program was utilized to visualize the complexes. Hydrogen bonds, salt bridges, and non-bonded contacts between Spike and IFITM protein chains in the complexes were detected with the PDBsum web-based tool. The best binding energy among the 6VYB-IFITM wild protein complexes belong to 6VYB-IFITM1 (-46.16 kcal/mol). Likewise, among the 6VXX-IFITM wild protein complexes, the most negative binding energy belongs to 6VXX-IFITM1 (-52.42 kcal/mol). An interesting result found in the study is the presence of hydrogen bonds between the cytoplasmic domain of the IFITM1 wild protein and the S2 domain of 6VYB. Among the Spike-IFITM mutant protein complexes, the best binding energy belongs to the 6VXX-IFITM2 N63S complex (-50.77 kcal/mol) and the worst binding energy belongs to the 6VXX-IFITM3 S50T complex (4.86 kcal/mol).

The study suggests that IFITM1 protein may act as a receptor for SARS-CoV-2 Spike protein. Assays must be advanced from in silico to in vitro for the determination of the receptor-ligand interactions between IFITM proteins and SARS-CoV-2.