Amyloidogenesis of SARS-CoV-2 delta plus and omicron variants receptor-binding domain (RBD): impact of SUMO fusion tag.

Purpose: The RBD of SARS-CoV-2 mediates viral entry into host cells by binding to the host receptor ACE2. SARS-CoV-2 infection is linked to various health issues resembling amyloid-related problems, persuading us to investigate the amyloidogenicity of the SARS-CoV-2 spike RBD.

Methods: The FoldAmyloid program was used to assess the amyloidogenic propensities in the RBD of Delta Plus and RBD of the Omicron variant, with and without the SUMO tag. After the expression of RBDs, purification, and dialysis steps were performed, subsequently the ThT assay, FTIR, and TEM were employed to check the RBD ability to form fibrils.

Results: The ThT assay, TEM, and FTIR revealed the ability of RBD to self-assemble into β-sheet-rich aggregates (48.4% β-sheet content). Additionally, the presence of the SUMO tag reduced the formation of RBD amyloid-like fibrils. The amyloidogenic potential of Omicron RBD was higher than Delta Plus, according to both in silico and experimental analyses.

Conclusions: The SARS-CoV-2 RBD can assemble itself by forming aggregates containing amyloid-like fibrils and the presence of a SUMO tag can significantly decrease the formation of RBD amyloid-like fibrils. In silico analysis suggested that variation in the ThT fluorescence intensity of amyloid accumulations in the two SARS-CoV-2 strains arises from specific mutations in their RBD regions.