Secondary conformation of MERS-CoV, SARS-CoV and SARS-CoV-2 Spike Proteins revealed by Infrared Vibrational Spectroscopy

Abstract

All coronaviruses are characterized by spike glycoproteins whose S1 subunit contains the receptor binding domain anchoring the virus to the host cellular membrane and regulating virus transmissibility and infectious process. Although the protein/receptor interaction depends on the spike secondary-conformation, in particular to its S1 unit, few is known about the secondary-structure of different coronaviruses. In this paper the S1 conformation is investigated for MERS-CoV, SARS-CoV and SARS-CoV-2 in serological condition, by measuring their Amide I infrared vibrational absorption bands. The SARS-CoV-2 secondary structure reveals a strong difference in comparison to MERS-CoV and SARS-CoV ones, with a higher amount of intermolecular β-sheet content. Moreover, the conformation of SARS-CoV-2 S1 shows a significant change by moving from serological pH and mild acidic to alkaline pH conditions close to the bat ecological niche. Both results suggest a huge capability of SARS-CoV-2 S1 glycoprotein to adapt its secondary structure to different environments.