Structural characterization of the HCoV-229E fusion core

Abstract

HCoV-229E spike (S) protein mediates virion attachment to cells and subsequent fusion of the viral and cellular membranes. This protein is composed of an N-terminal receptor-binding domain (S1) and a C-terminal trans-membrane fusion domain (S2). S2 contains a highly conserved heptad repeat 1 and 2 (HR1 and HR2). In this study, the HRs sequences were designed and connected with a flexible linker. The recombinant fusion core protein was crystallized and its structure was solved at a resolution of 2.45 Å. Then we characterized the binding of HR1s and HR2s via both sequence alignment and structural analysis. The overall structures, especially the residues in some positions of HR2 are highly conserved. Fourteen hydrophobic and three polar residues from each HR1 peptide are packed in layers at the coiled-coil interface. These core amino acids can be grouped into seven heptad repeats. Analysis of hydrophobic and hydrophilic interactions between HR2 helix and HR1 helices, shows that the HR1 and HR2 polypeptides are highly complementary in both shape and chemical properties. Furthermore, the available knowledge concerning HCoV-229E fusion core may make it possible to design small molecule or polypeptide drugs targeting membrane fusion, a crucial step of HCoV-229E infection.

The human coronavirus HCoV-229E S-protein structure and receptor binding

“…The S2 subunit is largely alpha-helical and the three longest helices, helix 629-652 (UH), helix 821- 852 (HR1 821-852 ) and helix 873-918 (the central helix, CH), form the helical core region of each S2 subunit (Figure 4f,g). The HR1 821-852 helix is only a portion of the HR1 segment that forms the central 3-helix coiled-coil of the post-fusion 6-helix bundle Zhang et al, 2018). The remainder of HR1 is made up of two shorter helices and two non-helical segments (Figure 4g).…”

“…In the up conformation, it is exposed for receptor binding and data exist to suggest that the RBD up conformation may promote conversion to the post-fusion form . The post-fusion form of the coronavirus S-protein is characterized by a 6-helix bundle formed by the inner HR1 triple-helical coiled-coil around which the HR2 helices are packed (Xu et al, 2004;Yan et al, 2018;Zhang et al, 2018). The coronavirus S2 subunit is large and the structural changes that accompany conversion to the post-fusion conformation are extensive (Walls et al, 2017).…”

Crystal structure of the post-fusion core of theHuman coronavirus 229Espike protein at 1.86 Å resolution

“…Such a structure is typical for the CoV fusion core and represents the post-fusion state of the HCoV-229E spike protein. As our structure is at higher resolution and the HR1 and HR2 motifs are more complete than in Zhang et al (2018), we therefore used our HCoV-229E structure in the following comparisons of different HCoVs.…”

“…(f, g) Sequence alignment of the HR1 region ( f ) and HR2 region (g) of HCoV-229E, HCoV-NL63, HCoV-HKU1, HCoV-OC43, SARS and MERS. The HR1 and HR2 coverages of previous HCoV structures (PDB entry 2ieq for HCoV-NL63, PDB entry 1wyy for SARS and PDB entry 4njl for MERS) and the recently reported HCoV-229E structure (PDB entry 5zhy; Zhang et al, 2018) are depicted with a yellow background. The HCoV-229E structure presented here is denoted with a cyan highlight.…”

“…Nevertheless, structural elucidation of the interaction research papers between HCoV-229E and APN was only revealed very recently (Wong et al, 2017). More recently, a crystal structure of the HCoV-229E fusion core (HR1 residues 788-838 and HR2 residues 1060-1097) was reported at 2.45 Å resolution (Zhang et al, 2018) while we were preparing this manuscript.…”