DETERMINANTS ESSENTIAL FOR THE TRANSMISSIBLE GASTROENTERITIS VIRUS-RECEPTOR INTERACTION RESIDE WITHIN A DOMAIN OF AMINOPEPTIDASE-N THAT IS DISTINCT FROM THE ENZYMATIC SITE

The swine-specific coronavirus transmissible gastroenteritis virus (TGEV) uses pig aminopeptidase-N (pAPN) as a cellular receptor. We showed that the human aminopeptidase-N (hAPN) cannot substitute for pAPN in this respect, although the two enzymes have 80% amino acid sequence identity. In order to map the TGEV binding site on pAPN, we constructed a series of APN cDNA chimeras between pAPN and hAPN and analyzed them for their capacity to confer infectivity. The region between residues 717 and 813 was found to be essential for infectivity. This region also contains the epitopes for three TGEV-blocking monoclonal antibodies directed against pAPN. These data support the view that the catalytic site and the TGEV receptor site are located in different domains. Moreover, APN inhibitors and mutations in the catalytic site had no obvious effect on permissiveness for virus, thus providing evidence that the APN enzymatic activity is not involved in the process of infection.