Mutational Analysis of Aminopeptidase N, a Receptor for Several Group 1 Coronaviruses, Identifies Key Determinants of Viral Host Range

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Abstract
Feline coronavirus (FCoV), porcine transmissible gastroenteritis coronavirus (TGEV), canine coronavirus (CCoV), and human coronavirus HCoV-229E, which belong to the group 1 coronavirus, use aminopeptidase N (APN) of their natural host and feline APN (fAPN) as receptors. Using mouse-feline APN chimeras, we identified three small, discontinuous regions, amino acids (aa) 288 to 290, aa 732 to 746 (called R1), and aa 764 to 788 (called R2) in fAPN that determined the host ranges of these coronaviruses. Blockade of infection with anti-fAPN monoclonal antibody RG4 suggested that these three regions lie close together on the fAPN surface. Different residues in fAPN were required for infection with each coronavirus. HCoV-229E infection was blocked by an N-glycosylation sequon present between aa 288 to 290 in murine APN. TGEV required R1 of fAPN, while FCoV and CCoV required both R1 and R2 for entry. N740 and T742 in fAPN and the homologous R741 in human APN (hAPN) were key determinants of host range for FCoV, TGEV, and CCoV. Residue N740 in fAPN was essential only for CCoV receptor activity. A conservative T742V substitution or a T742R substitution in fAPN destroyed receptor activity for the pig, dog, and cat coronaviruses, while a T742S substitution retained these receptor activities. Thus, the hydroxyl on T742 is required for the coronavirus receptor activity of fAPN. In hAPN an R741T substitution caused a gain of receptor activity for TGEV but not for FCoV or CCoV. Therefore, entry and host range of these group 1 coronaviruses depend on the ability of the viral spike glycoproteins to recognize small, species-specific amino acid differences in the APN proteins of different species.