Uncovering the structural flexibility of SARS-CoV-2 glycoprotein spike variants

The severe acute respiratory syndrome CoV-2 rapidly spread worldwide, causing a pandemic. After a period of evolutionary stasis, a set of SARS-CoV-2 mutations has arisen in the spike, the leading glycoprotein at the viral envelope and the primary antigenic candidate for vaccines against the 2019 CoV disease (COVID-19). Here, we present comparative biochemical data of the glycosylated full-length ancestral and D614G spike together with three other highly transmissible strains classified by the World Health Organization as variants of concern (VOC): beta, gamma, and delta. By showing that only D614G early variant has less hydrophobic surface exposure and trimer persistence at mid-temperatures, we place D614G with features that support a model of temporary fitness advantage for virus spillover worldwide. Further, during the SARS-CoV-2 adaptation, the spike accumulates alterations leading to less structural rigidity. The decreased trimer stability observed for the ancestral and the gamma strain and the presence of D614G uncoupled conformations mean higher ACE-2 affinities when compared to the beta and delta strains. Mapping the energetic landscape and flexibility of spike variants is necessary to improve vaccine development.