Fig. 1: Vaccine design and characterization of the expressed antigens.

a, Structure of BNT162b1 and BNT162b2 RNA. UTR, untranslated region; SP, signal peptide. The proline subsitutions of S(P2) (K986P and V897P) are indicated. b, Liquid capillary electropherograms of in vitro-transcribed BNT162b1 and BNT162b2 RNA. Peaks represent individual samples merged into one graph. c, Representative 2D class averages from electron microscopy of negatively stained RBD–foldon trimers. Box edge, 37 nm. d, Two-dimensional class average from cryo-EM of the ACE2–B⁰AT1–RBD–foldon trimer complex. Long box edge, 39.2 nm. Peripheral to the relatively well-defined density of each RBD domain bound to ACE2, there is diffuse density that we attribute to the remainder of the flexibly tethered RBD–foldon trimer. A detergent micelle forms the density at the end of the complex opposite the RBD–foldon. e, Density map of the ACE2–B⁰AT1–RBD–foldon trimer complex at 3.24 Å, after focused refinement of the ACE2 extracellular domain bound to a RBD monomer. Surface colour-coding is by subunit. The ribbon model refined to the density shows the RBD–ACE2 binding interface.Residues that potentially mediate polar interactions are labelled. f, A 3.29 Å cryo-EM map of S(P2) with fitted and refined atomic model, viewed down the threefold axis towards the membrane (left) and viewed perpendicular to the threefold axis (right). The map is coloured by protomer. g, Mass density map of TwinStrep-tagged S(P2) produced by 3D classification of images extracted from cryo-EM micrographs with no symmetry averaging, showing the class in the one-RBD-up and two-RBD-down position.