Structural and Molecular Evidence Suggesting Coronavirus-driven Evolution of Mouse Receptor

Abstract

Hosts and pathogens are locked in an evolutionary arms race. To infect mice, mouse hepatitis coronavirus (MHV) has evolved to recognize mouse CEACAM1a (mCEACAM1a) as its receptor. To elude MHV infections, mice may have evolved a variant allele from the gene, called, producing mCEACAM1b, which is a much poorer MHV receptor than mCEACAM1a. Previous studies showed that sequence differences between mCEACAM1a and mCEACAM1b in a critical MHV-binding CC' loop partially account for the low receptor activity of mCEACAM1b, but detailed structural and molecular mechanisms for the differential MHV receptor activities of mCEACAM1a and mCEACAM1b remained elusive. Here we have determined the crystal structure of mCEACAM1b and identified the structural differences and additional residue differences between mCEACAM1a and mCEACAM1b that affect MHV binding and entry. These differences include conformational alterations of the CC' loop as well as residue variations in other MHV-binding regions, including β-strands C' and C'' and loop C'C''. Using pseudovirus entry and protein-protein binding assays, we show that substituting the structural and residue features from mCEACAM1b into mCEACAM1a reduced the viral receptor activity of mCEACAM1a, whereas substituting the reverse changes from mCEACAM1a into mCEACAM1b increased the viral receptor activity of mCEACAM1b. These results elucidate the detailed molecular mechanism for how mice may have kept pace in the evolutionary arms race with MHV by undergoing structural and residue changes in the MHV receptor, providing insight into this possible example of pathogen-driven evolution of a host receptor protein.

Structure of mouse coronavirus spike protein complexed with receptor reveals mechanism for viral entry

“…Briefly, the protein was harvested from cell culture medium, and purified sequentially on Ni-NTA column and Superdex 200 size exclusion column (GE Healthcare). Mouse CEACAM1a ectodomain (residues 1-202) was expressed and purified as previously described [22,34]; the construct contained a C-terminal His 6 tag. Purified MHV S-e and CEA-CAM1a were mixed and incubate at 4˚C for 2 hours.…”

Cryo-EM structure of infectious bronchitis coronavirus spike protein reveals structural and functional evolution of coronavirus spike proteins

“…PDB IDs for mouse hepatitis coronavirus (MHV) and MERS coronavirus are 3JCL and 5X5F, respectively. CEACAM1b (PDB ID: 5VST), whose β-sandwich fold is topologically different from that of coronavirus S1-NTDs [59], was used as a negative control. N.D.: no detectable structural similarity.…”

Evolution: Decoy Receptors as Unique Weapons to Fight Pathogens

“…Alternatively, viral pathogens such as the mouse hepatitis virus (MHV) [17] may have appropriated CEACAM1 as a receptor. Viruses in general are highly dependent on just one entry receptor, which can probably be more easily counteracted by the host through fixation of non-binding receptor alleles as found for MHV [18]. In this case, decoy receptors might not be required for defense.…”