Fig. 1: Characterization of SARS-CoV-2 S mutants containing single stabilizing mutations.

a Analytical SEC of S variants on an SRT-10C SEC-500 15 cm column showing the trimer peak (solid line) relative to the control, which is the un-mutated backbone (dashed line). b ACE2-Fc binding to S protein mutants based on AlphaLISA of ΔFurin variants (left panel) and S-2P (right panel). Data are represented as mean + SD of n = 4 biologically independent samples in one experiment. Mutants were grouped according to the structural regions indicated in light gray. c Temperature stability of purified S trimers as measured by DSC. Two melting events are indicated by Tm1 and Tm2. c (left panel) Uncleaved SARS2-S variants with furin site mutations (ΔFurin), with one stabilizing proline mutation in the hinge loop (ΔFurin K986P or ΔFurin V987P), and both proline mutations in the hinge loop (S-2P); (middle panel) ΔFurin variants with indicated mutations in S1 and (right panel) ΔFurin variants with indicated mutations in S2. d Binding of SAD-S35, ACE2, and CR3022 to purified S proteins measured with BioLayer Interferometry, showing the initial slope V0 at the start of binding. Source data are provided as a Source Data file.