
<ArticleTitle>Molecular determinants of species specificity in the coronavirus receptor <prot>aminopeptidase N</prot> (<prot>CD13</prot>): influence of N-linked glycosylation.</ArticleTitle>
<AbstractText><prot>Aminopeptidase N</prot> (<prot>APN</prot>), a 150-kDa metalloprotease also called <prot>CD13</prot>, serves as a receptor for serologically related coronaviruses of humans (human coronavirus 229E [<prot>HCoV-229E</prot>]), pigs, and cats. These virus-receptor interactions can be highly species specific; for example, the human coronavirus can use human <prot>APN</prot> (<prot>hAPN</prot>) but not porcine <prot>APN</prot> (<prot>pAPN</prot>) as its cellular receptor, and porcine coronaviruses can use <prot>pAPN</prot> but not <prot>hAPN</prot>. Substitution of <prot>pAPN</prot> amino acids 283 to 290 into <prot>hAPN</prot> for the corresponding amino acids 288 to 295 introduced an N-glycosylation sequon at amino acids 291 to 293 that blocked <prot><prot>HCoV-229E</prot> receptor</prot> activity of <prot>hAPN</prot>. Substitution of two amino acids that inserted an N-glycosylation site at amino acid 291 also resulted in a mutant <prot>hAPN</prot> that lacked receptor activity because it failed to bind <prot>HCoV-229E</prot>. Single amino acid revertants that removed this sequon at amino acids 291 to 293 but had one or five <prot>pAPN</prot> amino acid substitution(s) in this region all regained <prot>HCoV-229E</prot> binding and receptor activities. To determine if other N-linked glycosylation differences between <prot>hAPN</prot>, feline <prot>APN</prot> (<prot>fAPN</prot>), and <prot>pAPN</prot> account for receptor specificity of pig and cat coronaviruses, a mutant <prot>hAPN</prot> protein that, like <prot>fAPN</prot> and <prot>pAPN</prot>, lacked a glycosylation sequon at 818 to 820 was studied. This sequon is within the region that determines receptor activity for porcine and feline coronaviruses. Mutant <prot>hAPN</prot> lacking the sequon at amino acids 818 to 820 maintained <prot><prot>HCoV-229E</prot> receptor</prot> activity but did not gain receptor activity for porcine or feline coronaviruses. Thus, certain differences in glycosylation between coronavirus receptors from different species are critical determinants in the species specificity of infection.</AbstractText>
