Molecular Interactions of Group 1 Coronaviruses with Feline APN

Abstract

Most coronaviruses in phylogenetic group 1 can cause disease in only one animal species. Within group 1, porcine transmissible gastroenteritis virus (TGEV), feline infectious peritonitis virus (FIPV), human coronavirus 229E (HCoV-229E), and canine coronavirus (CCoV) use aminopeptidase N (APN) from their natural host for entry and infection of cells. APN is a highly conserved type II transmembrane glycoprotein in mammals (70– 80% at the amino acid level). Remarkably, although each of these group 1 coronaviruses uses APN of its normal host for entry, all of them can also use feline APN (fAPN) as a receptor for entry and infection in cell culture. Previous studies used chimeras between APN proteins of different species to identify domains in APN that are required for coronavirus receptor activity. Studies on receptor specificities of chimeras between human and feline APN or pig and human APN suggest that the spike glycoproteins of TGEV, FIPV, and HCoV-229E interact with two discontinous regions within APN. Also, species-specific N-linked glycosylations in APN can affect receptor activity for HCoV-229E. In in vivo studies, transgenic mice expressing human APN (hAPN) were resistant to infection with HCoV-229E, but cells harvested from the transgenic mice were susceptible to HCoV-229E. hAPN transgenic mice in a Stat-1 knockout background (hAPN Stat ) were susceptible to HCoV-229E, which was adapted for growth in cells from these double transgenic mice. These studies suggest that other host factors in addition to the receptor are needed for infection in vivo. In this study, we used chimeras between mouse APN (mAPN) and fAPN to identify domains of fAPN that are necessary for entry by group 1 coronaviruses. Baby hamster