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. Author manuscript; available in PMC: 2017 Jun 5.
Published in final edited form as: Annu Rev Virol. 2016 Aug 25;3(1):237–261. doi: 10.1146/annurev-virology-110615-042301

Figure 1.

Figure 1

Introduction to coronaviruses and their spike proteins. (a) Classification of coronaviruses. Representative coronaviruses in each genus are human coronavirus NL63 (HCoV-NL63), porcine transmissible gastroenteritis coronavirus (TGEV), porcine epidemic diarrhea coronavirus (PEDV), and porcine respiratory coronavirus (PRCV) in the genus Alphacoronavirus; severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), bat coronavirus HKU4, mouse hepatitis coronavirus (MHV), bovine coronavirus (BCoV), and human coronavirus OC43 in the genus Betacoronavirus; avian infectious bronchitis coronavirus (IBV) in the genus Gammacoronavirus; and porcine deltacoronavirus (PdCV) in the genus Deltacoronavirus. (b) Schematic of the overall structure of prefusion coronavirus spikes. Shown are the receptor-binding subunit S1, the membrane-fusion subunit S2, the transmembrane anchor (TM), the intracellular tail (IC), and the viral envelope. (c) Schematic of the domain structure of coronavirus spikes, including the S1 N-terminal domain (S1-NTD), the S1 C-terminal domain (S1-CTD), the fusion peptide (FP), and heptad repeat regions N and C (HR-N and HR-C). Scissors indicate two proteolysis sites in coronavirus spikes. (d) Summary of the structures and functions of coronavirus spikes. Host receptors recognized by either of the S1 domains are angiotensin-converting enzyme 2 (ACE2), aminopeptidase N (APN), dipeptidyl peptidase 4 (DPP4), carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), and sugar. The available crystal structures of S1 domains and S2 HRs are shown. Their PDB IDs are 3KBH for HCoV-NL63 S1-CTD, 4F5C for PRCV S1-CTD, 2AJF for SARS-CoV S1-CTD, 4KR0 for MERS-CoV S1-CTD, 3R4D for MHV S1-NTD, 4H14 for BCoV S1-NTD, 2IEQ for HCoV-NL63 HRs, 1WYY for SARS-CoV HRs, 4NJL for MERS-CoV HRs, and 1WDF for MHV HRs.