Figure 1: Inhibition of HKU1 virus infection by 1A-S310-677aa.

(a) Schematic diagram of HKU1 S protein, modified from Kirchdoerfer et al¹⁸. NTD, N-terminal domain; CTD, C-terminal domain; SD-1, subdomain-1; SD-2, subdomain-2; RBD, receptor-binding domain; FP, fusion peptide; HR-N, N-terminal heptad repeat; HR-C, C-terminal heptad repeat; TMD, transmembrane domain; cleavage site, furin cleavage site between S1 and S2. The amino acid numbers are from the S protein of genotype A HKU1 virus. (b) ELISA was performed using purified 1A-S310-677aa and purified antibodies. The experiments were done in triplicate and the s.d.‘s (n=3) were shown as error bar. The experiments were performed twice and one representative is shown. Differentiated HTBE cells were incubated with 20 μM of 1A-310-677aa protein at 37 °C for 1 h. HKU1 viruses were diluted into the same amount of proteins and added onto HTBE cells for 4 h. Forty-eight hours after inoculation, cells were fixed and stained with polyclonal rabbit anti HKU1 S antibodies 1814 at a dilution at 1:100 (c), and released viruses at 24 h post inoculation from apical wash were analysed using real-time PCR (d). The amount of HKU1 viral RNA from BSA control was set as 100%. Scale bar, 50 μm. The experiments were done in triplicate and the s.d.‘s (n=3) were shown as error bar. The experiments were performed twice and one representative is shown.