Significance We report here a 3.3-Å cryo-EM structure of feline infectious peritonitis virus (FIPV) S protein derived from the serotype I FIPV UU4 strain. The near-atomic EM map enabled ab initio modeling of 27 out of the 33 experimentally verified high-mannose and complex-type N-glycans that mask most of the protein surface. We demonstrated the feasibility to directly visualize the core fucose of a complex-type glycan, which was independently cross-validated by glycopeptide mass spectrometry analyses. There exist 3 N-glycans that wedge between 2 galectin-like domains within the S1 subunit of FIPV-UU4 S protein, resulting in a propeller-like conformation unique to all reported CoV S proteins. The results highlight a structural role of glycosylation in maintaining complex protein structures. Feline infectious peritonitis virus (FIPV) is an alphacoronavirus that causes a nearly 100% mortality rate without effective treatment. Here we report a 3.3-Å cryoelectron microscopy (cryo-EM) structure of the serotype I FIPV spike (S) protein, which is responsible for host recognition and viral entry. Mass spectrometry provided site-specific compositions of densely distributed high-mannose and complex-type N – glycans that account for 1/4 of the total molecular mass; most of the N-glycans could be visualized by cryo-EM. Specifically, the N-glycans that wedge between 2 galectin-like domains within the S1 subunit of FIPV S protein result in a unique propeller-like conformation, underscoring the importance of glycosylation in maintaining protein structures. The cleavage site within the S2 subunit responsible for activation also showed distinct structural features and glycosylation. These structural insights provide a blueprint for a better molecular understanding of the pathogenesis of FIP.
【저자키워드】 mass spectrometry, Cryoelectron microscopy, alphacoronavirus, Feline infectious peritonitis virus, protein glycosylation, 【초록키워드】 Treatment, Pathogenesis, S protein, glycosylation, feasibility, virus, viral entry, Protein, Microscopy, CoV, cryo-EM, mortality rate, molecular, S2 subunit, glycan, structures, N-glycan, Feline infectious peritonitis, Activation, serotype, domain, S proteins, cleavage site, Host, cryo-EM structure, feature, effective, highlight, responsible, resulting, the S1 subunit, reported, provided, unique, demonstrated, cause, analyses, complex protein, high-mannose, Significance, 【제목키워드】 coronavirus spike protein, glycan, Analysis, unique, reveal,