Introduction
Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV), Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV), and the recently identified novel Coronavirus (SARS-CoV-2) belong to the Coronaviridae family, genus Betacoronavirus, that has been related to important epidemiological outbreaks. These are enveloped viruses with a positive-sense single-strand RNA of around 32 Kb. The viral particles contain four main structural proteins: the spike, membrane, envelope protein, and nucleocapsid. The spike protein protrudes from the envelope of the virion and plays a pivotal role in the receptor host selectivity and cellular attachment. Strong scientific evidence showed that SARS and SARS-CoV-2 spike proteins interact with angiotensin-converting enzyme 2 (ACE2) (Chen et al 2020[2]; Wan et al., 2020[16]). Also, other cellular receptors play a secondary role in the viral attachment, as the C-type lectin CD209L, and DC-SIGN binds to SARS-CoV. However, ACE2 appears to be the key functional receptor for the SARS-CoV (Coutard et al., 2020[3]; Satija and Lal, 2007[12]) and probably for SARS-CoV-2 (Walls et al., 2020[15]) The interaction between the viral protein and its cell membrane receptor is a critical step in the replication cycle. Furthermore, the efficiency of viral infection is strongly dependent on this process. Several physicochemical factors are associated with protein-protein interactions. These factors are determined by the nature of residues and the type of chemical interactions occurring between ligand and receptor. Thus, the presence of residues that produce an energetically favored interaction (lower free energy) may drive binding kinetics and finally lead to the fusion event. Based on that, this study aimed to evaluate the energetic profile of the interaction between the SARS-CoV-2 spike protein and the human cell receptor ACE2.