ART4 and infection: HS binding has been clearly demonstrated for MHV, where infection by MHV-A59 strain (which is solely dependent on mCEACAM1a binding for entry), led to the emergence of variant strains with mutations and a short 7 amino acid insertion in the S1 subunit; 492TQTTRTKKVPKPKS505 that introduces multibasic sites at different locations within the S glycoprotein [248,249].