Best talk award - XXVIII School of pure and applied biophysics: "Molecule in(ter)action: from nano to macroscale", SIBPA

Spike (S) glycoprotein is the largest structural protein of SARS-CoV-2 virus and the first involved in the anchoring of the host receptor angiotensin-converting enzyme 2 (ACE2) through the receptor binding domain (RBD). It is composed by two subunits: S1, responsible for recognition/anchoring to the host receptor ACE2 and containing the RBD; S2, responsible for the membrane fusion. The secondary structure characterization of S protein and its components is important to understand and shed light on the mechanisms occurring in the viral process, from their functionality to pathogenesis, finally to spectral fingerprint for the design of optical biosensors. In this work the whole monomeric S protein and its domains, such as RBD, S1 and S2 are investigated at serological pH (7.4) using Attenuated Total Reflectance Infrared spectroscopy (ATR-IR), one of the main techniques used in the secondary structure analysis of proteins. In order to obtain an estimation of the secondary structure percentage of each protein, the spectra analyses are focused on the Amide I band (1600-1700 cm-1), which are deconvoluted into gaussian curves associated with a specific secondary structure. Furthermore, being the S1 the first part involved in the viral process, it is useful to study its secondary structure alterations under chemical/physical environmental modifications. For this reason, we performed a study on the S1 subunit under pH and temperature variations, observing how the S1 protein adapts its secondary structure to different inhospitable surroundings. The high stable configuration is present at endosomal pH 5.5 and at temperature of 30 C, proving that the protein evolution modifications yield the protein more performant.