title: N-terminal domain of the murine coronavirus receptor CEACAM1 is responsible for fusogenic activation and conformational changes of the spike protein.
abstract: The mouse hepatitis virus (MHV) receptor (MHVR), CEACAM1, has two different functions for MHV entry into cells: binding to MHV spike protein (S protein) and activation of the S protein to execute virus-cell membrane fusion, the latter of which is accompanied by conformational changes of the S protein. The MHVR comprising the N-terminal and fourth domains [R1(1,4)] displays these two activities, and the N domain is thought to be critical for binding to MHV. In this study, we have addressed whether or not the N domain alone is sufficient for these activities. We examined three types of soluble form MHVR (soMHVR), one consisting of the N domain alone [soR1(1)], one with the N and second domains [soR1(1,2)], and one [soR1(1,4)] expressed by recombinant baculoviruses. We assessed the abilities of these three types of soMHVR to bind to MHV, activate fusogenicity, and induce conformational changes of the S protein. All three types of soMHVR similarly bound to MHV, as examined by a solid-phase binding assay and neutralized MHV infectivity. They also activated S protein fusogenicity and induced its conformational changes with similar levels of efficiency. However, R1(1) expressed on the BHK cell surface failed to serve as a receptor in spite of a sufficient level of expression. The inability of expressed R1(1) to work as a receptor was due to the inaccessibility of virions to R1(1); however, these were accessible using the MHVR-specific monoclonal antibody CC1. These results collectively indicated that the N domain retains all biological activities necessary for receptor function.
authors.affiliation: National Institute of Neuroscience, NCNP, Kodaira, Tokyo 187-8502, Japan.
authors.forename: Hideka S
authors.initials: HS
authors.lastname: Miura
authors.forename: Keiko
authors.initials: K
authors.lastname: Nakagaki
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Taguchi
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000737:chemistry* / Q000378:metabolism; D000943:Antigens, Differentiation / Q000737:chemistry* / Q000378:metabolism; D002272:Carcinoembryonic Antigen; D015815:Cell Adhesion Molecules; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D005434:Flow Cytometry; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006517:Murine hepatitis virus / Q000378:metabolism / Q000472:pathogenicity* / Q000502:physiology; D009500:Neutralization Tests; D011487:Protein Conformation; D011991:Receptors, Virus / Q000737:chemistry* / Q000378:metabolism; D064370:Spike Glycoprotein, Coronavirus; D013329:Structure-Activity Relationship; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; C069847:CD66 antigens; D002272:Carcinoembryonic Antigen; C486183:Ceacam1 protein, mouse; D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins; D011991:Receptors, Virus; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus