FIG. 1.

The SARS-CoV/receptor interface. (A) Alignment of residues on the SARS-CoV RBD at the interface that have undergone evolution. In red are two residues, residues 479 and 487, that determine the major species barriers between human and civet for SARS-CoV infections. Four prototypic viral strains are defined in the text. (B) Alignment of residues on the N-terminal helix of ACE2 that differ between human and civet. In red are residues that directly interact with SARS-CoV. (C) Crystal structure of the interface between hTor02 RBD and chimeric ACE2 bearing the N-terminal helix from civet and the remaining peptidase domain from human. The receptor-binding motif (RBM) on hTor02 RBD is in red, with side chains of the four residues that have undergone evolution (residues 472, 479, 480, and 487). The N-terminal helix from civet ACE2 is in green, with side chains of residues that differ between human and civet. The rest of peptidase domain from human ACE2 is in yellow. (D) An overall view of the crystal structure of human-civet chimeric ACE2 complexed with hTor02 RBD. The structure is rotated clockwise in depth compared with the structure in panel C. The illustrations were made using Povscript (4).