The recent outbreaks of severe acute respiratory syndrome (SARS), the Middle East respiratory syndrome (MERS), and the severe pig pandemics caused by the emerging porcine coronavirus, remind us how infection by coronaviruses can impact our health and socioeconomics. Coronaviruses also infect cats and cause feline infectious peritonitis (FIP). Due to the difficulty of diagnosis and the lack of effective treatment and prevention methods, the fatality rate is almost 100% once a cat contracted the most prevalent serotype I cat infectious peritonitis. It, therefore, poses an urgent issue for veterinarians.
To better understand the molecular basis of cat infectious peritonitis, Dr. Shang-Te Danny Hsu from the Institute of Biological Chemistry, Academia Sinica, teamed up with his colleague Dr. Kay-Hooi Khoo from the same institute, and Prof. Hui-Wen Chang and Prof. Yen-Chen Chang from the Institute of Molecular and Comparative Pathobiology, College of Bioresources and Agriculture, National Taiwan University (NTU), to carry out an interdisciplinary investigation into the structure and function of the spike protein of type 1 feline infectious peritonitis virus (FIPV). The spike protein of coronavirus is an essential target because it is used to recognize specific host cells and facilitate viral entry, which represents the first step of viral infection.
Using the recently established, state-of-the-art cryo-electron microscopy (cryo-EM) facility at Academia Sinica, the team successfully determined a high-resolution atomic model of the spike protein of FIPV. It adopts a novel structural arrangement that is entirely different from the previously reported molecular structures of SARS and MERS spike proteins. Furthermore, the team used advanced biophysical and mass spectrometry techniques to elucidate complex post-translationally modified glycation structures that were directly visualized by cryo-EM single-molecule structure reconstruction analysis. The molecular model revealed how the spike protein structure is densely decorated by the glycan moieties that can help evade the host immune system. These glycans may also play an essential role in host recognition. These detailed molecular insights were made possible thanks to Academia Sinica’s world-class research expertise in glycobiology. This work is published in the Proceedings of the National Academy of Sciences, U. S. A. in January 2020 https://www.pnas.org/content/early/2020/01/02/1908898117.
Reminiscent of locks and keys, viruses recognize their hosts by finding receptor molecules on the host cell surface that have complementary shapes to the viral spike proteins. Likewise, host immune systems utilize a repertoire of antibodies that recognize specific shapes of foreign antigens, such as the viral spike proteins, to trigger immune responses for self-defense. It is important to note that the emergence of SARS and MERS is the result of mutations on the spike proteins of coronaviruses that initially target civet and camel, respectively. These mutations lead to subtle changes in the molecular configuration of the spike proteins that result in host jump, allowing the virus to spread to humans. A better understanding of the molecular structure of the spike protein of FIPV therefore, not only gives us the key to a mechanistic understanding of FIP, but broadens our general knowledge of the underlying mechanism of coronavirus infection. We envisage that this study will facilitate diagnosis and vaccine design targeting FIPV. Importantly, the integrated research platform that combines advanced cryo-EM and mass spectrometry will play a crucial role in future studies of viral glycoprotein structures that could mitigate negative socioeconomic effects and make significant contributions to national health care.
This work is supported by Academia Sinica, National Taiwan University, Taiwan Protein Project, and the Ministry of Science and Technology. The first author, Tzu-Jing Yang, is a Ph.D. student of the Institute of Biochemical Sciences, NTU. The other first author, Yen-Chen Chang, was a Ph.D. student at the Institute of Molecular and Comparative Pathobiology, College of Bioresources and Agriculture, NTU, and a postdoctoral fellow at Dr. Hsu’s lab, is now an assistant professor at her alma mater.
Shang-Te Danny Hsu’s lab website https://sites.google.com/site/hsushangte/about-pi-chinese
Hui-Wen Chang’s lab website http://www.vm.ntu.edu.tw/DVM/teachers1/teacher40.html
Academia Sinica Cryo-EM Center http://cryoem.ibc.sinica.edu.tw/
Academia Sinica Common MS Facilities https://sites.google.com/view/ascmsf/
Article title: “Cryo-EM Analysis of a Feline Coronavirus Spike Protein Reveals a Unique Structure and Camouflaging Glycans”
Article link: https://doi.org/10.1073/pnas.1908898117