Fig. 1: Cryo-EM structures of HKU1 spike S1-RBD in complex with TMPRSS2.
a Schematic diagrams of HKU1 spike S1-RBD and TMPRSS2 constructs. b, c BLI titrations of 1A RBD–TMPRSS2 (b) and 1B RBD–TMPRSS2 (c); the KD values of binding are indicated. Data fitting is shown with red curves. d Cryo-EM structure of HKU1 1A RBD (orange) in complex with TMPRSS2 (purple); left, cryo-EM densities, right, ribbon models. e Cryo-EM structure of HKU1 1B RBD (magenta) in complex with TMPRSS2 (blue); left, cryo-EM densities, right, ribbon models. Sugars are colored green. f 1B RBD and TMPRSS2 interaction shown with ribbon models. HKU1 receptor binding groove (RBG) is indicated. g Sequence alignment of 1A-RBD and 1B-RBD illustrating 13 residues (marked by blue asterisks) of RBG important for TMPRSS2 binding. Two disulfide bridges stabilizing RBG are indicated. h, i Detailed interaction between HKU1 1B RBD and TMPRSS2. TMPRSS2 is shown with molecular surface (blue), the proteinase active site is colored red, and RBD binding site is colored yellow. HKU1 1B RBD is shown with ribbon model (magenta). Key interaction residues are shown with stick model. Magnified view focusing 1B-RBD β-hairpin–TMPRSS2 interaction (h) and 1B-RBD Proline-rich–TMPRSS2 interaction (i) are shown. j HKU1 RBD–TMPRSS2 complex. RBD core domain is colored orange, RBG is colored red, and the insertion domain (RBM) is colored magenta. The black box indicates the RBD–TMPRSS2 interface. k, l TMPRSS2 (blue) is modeled to an HKU1 spike trimer with one RBD in up-state. Ribbon model (k) and molecular surface (l) are shown. Sugars are shown with green spheres; the RBGs are colored red. m Top view of an HKU1 spike trimer in close-state. RBGs are colored red. n A working model of HKU1 spike protein-mediated receptor binding.
