Coronavirus hemagglutinin-esterase and spike proteins co-evolve for functional balance and optimal virion avidity

Yifei Lang; Wentao Li; Zeshi Li; Danielle Koerhuis; Arthur C.S. van den Burg; Erik Rozemuller; Berend-Jan Bosch; Frank J.M. van Kuppeveld; Geert-Jan P.H. Boons; Eric G. Huizinga; Hilde M. van der Schaar; Raoul J. de Groot

cell culture supernatant with BCoV HE-Fc 17 to final concentrations of 1 pg to 10 μg/ml, and allowed 155 infection to proceed for 120 hr. While in the absence of HE-Fc there was no sign of virus propagation 156 as detectable by IFA, concentrations of exogenous sialate-O-acetylesterase as low as 1 ng/ml to up to frequency in p3. As a result of this mutation, HE lectin affinity was regained albeit to levels solely 207 detectable by high-sensitivity nanobead hemagglutination assay, while esterase activity towards 208 clustered glycotopes in BSM increased 4-fold as compared to HE-Phe 211 Ala, but still remained 125-fold 209 lower than that of wildtype HE (sFig. 4). Apparently, the increase in HE function, minor as it may be, 210 provides a selective advantage, but apparently one that benefits both low and high affinity S variants, 211 because the mutation was found in cloned viruses of either type. 3.4 x 10 7 TCID50/ml, when measured in the presence or absence of exogenous HE-Fc, respectively.