Molecular basis of sarbecovirus evolution and receptor tropism in natural hosts, potential intermediate hosts, and humans

The spike protein of many sarbecoviruses binds to the angiotensin-converting enzyme 2 (ACE2) receptor and facilitates viral entry. The diversification of the sarbecovirus spike gene and the mammalian ACE2 gene suggests that sarbecoviruses and their hosts have co-evolved, and the genetic diversity in these genes affects the host tropism of sarbecoviruses. Better comprehending the evolutionary potential of sarbecoviruses can lead to preparedness for the next pandemic. However, the host tropism of sarbecoviruses is not fully understood. Here, we performed round-robin pseudovirus infection assays using 53 sarbecoviruses and ACE2s from 17 mammals to elucidate the ACE2 tropism of sarbecoviruses in natural hosts, potential intermediate hosts and humans. We determined the factors responsible for the ACE2 tropism of sarbecoviruses through structural, phylogenetic analyses, and infection experiments, revealing which substitutions can expand the host range of sarbecoviruses. These results highlight the mechanisms modulating host tropism throughout sarbecovirus evolution.