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Cryo-EM structure of SARS-CoV-2 prototype spike protein receptor-binding domain in complex with hippopotamus ACE2
Structural highlights
FunctionSPIKE_SARS2 attaches the virion to the cell membrane by interacting with host receptor, initiating the infection (By similarity). Binding to human ACE2 receptor and internalization of the virus into the endosomes of the host cell induces conformational changes in the Spike glycoprotein (PubMed:32142651, PubMed:32075877, PubMed:32155444). Uses also human TMPRSS2 for priming in human lung cells which is an essential step for viral entry (PubMed:32142651). Proteolysis by cathepsin CTSL may unmask the fusion peptide of S2 and activate membranes fusion within endosomes.[HAMAP-Rule:MF_04099][1] [2] [3] mediates fusion of the virion and cellular membranes by acting as a class I viral fusion protein. Under the current model, the protein has at least three conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes.[HAMAP-Rule:MF_04099] Acts as a viral fusion peptide which is unmasked following S2 cleavage occurring upon virus endocytosis.[HAMAP-Rule:MF_04099] Publication Abstract from PubMedSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a wide range of hosts, including hippopotami, which are semi-aquatic mammals and phylogenetically closely related to Cetacea. In this study, we characterized the binding properties of hippopotamus angiotensin-converting enzyme 2 (hiACE2) to the spike (S) protein receptor binding domains (RBDs) of the SARS-CoV-2 prototype (PT) and variants of concern (VOCs). Furthermore, the cryo-electron microscopy (cryo-EM) structure of the SARS-CoV-2 PT S protein complexed with hiACE2 was resolved. Structural and mutational analyses revealed that L30 and F83, which are specific to hiACE2, played a crucial role in the hiACE2/SARS-CoV-2 RBD interaction. In addition, comparative and structural analysis of ACE2 orthologs suggested that the cetaceans may have the potential to be infected by SARS-CoV-2. These results provide crucial molecular insights into the susceptibility of hippopotami to SARS-CoV-2 and suggest the potential risk of SARS-CoV-2 VOCs spillover and the necessity for surveillance. IMPORTANCE: The hippopotami are the first semi-aquatic artiodactyl mammals wherein SARS-CoV-2 infection has been reported. Exploration of the invasion mechanism of SARS-CoV-2 will provide important information for the surveillance of SARS-CoV-2 in hippopotami, as well as other semi-aquatic mammals and cetaceans. Here, we found that hippopotamus ACE2 (hiACE2) could efficiently bind to the RBDs of the SARS-CoV-2 prototype (PT) and variants of concern (VOCs) and facilitate the transduction of SARS-CoV-2 PT and VOCs pseudoviruses into hiACE2-expressing cells. The cryo-EM structure of the SARS-CoV-2 PT S protein complexed with hiACE2 elucidated a few critical residues in the RBD/hiACE2 interface, especially L30 and F83 of hiACE2 which are unique to hiACE2 and contributed to the decreased binding affinity to PT RBD compared to human ACE2. Our work provides insight into cross-species transmission and highlights the necessity for monitoring host jumps and spillover events on SARS-CoV-2 in semi-aquatic/aquatic mammals. Molecular basis of hippopotamus ACE2 binding to SARS-CoV-2.,Yang R, Han P, Han P, Li D, Zhao R, Niu S, Liu K, Li S, Tian W-X, Gao GF J Virol. 2024 May 14;98(5):e0045124. doi: 10.1128/jvi.00451-24. Epub 2024 Apr 9. PMID:38591877[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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