Respected journal Science Magazine has published COVID-19 research led by Zhou Qiang from Westlake University in Hangzhou, China, which identifies the viral entry attachment stage for the new coronavirus (SARS-CoV-2).
The study reveals the cryo-electron microscopy (cryo-EM) structure of ACE2, an enzyme coating human cell membranes that is the cellular receptor for SARS-CoV-2; and its interaction with the receptor binding domain (RBD) of spike glycoproteins (S protein). Understanding the structure of SARS-CoV-2 is critical for drug development and can help exploration on suppressing this and future viral infections.
SARS-CoV-2 is a positive-strand RNA virus. Its genome is 80 percent similar to SARS-CoV identified in 2003, and it is generally believed that the infection process of SARS-CoV-2 may follow that of SARS-CoV. Information on the human receptor ACE2 however had been limited, as previous studies only provided basic structural information on its peptidase domain (PD). The Westlake research therefore focused on ACE2, revealing its full-length structure.
Closed and open conformations of ACE2
Researchers reconstructed the three-dimensional (3D) structure of ACE2 and found two conformations. ACE2 has two side chains with an N-terminal PD and a C-terminal collectrin-like domain (CLD) on each chain. Each side has a small extracellular domain, a long linker, and the single transmembrane (TM) helix. A ferredoxin-like fold domain links the PD to the TM helix, and is thus referred to as the neck domain. Both the PD and neck domains contribute to dimerization, however rotating the PDs results in their separation when the neck domain still dimerizes. The structure moves from “closed conformation” to “open conformation” after the PD rotation.
The Westlake researchers further examined the interaction between ACE2 and SARS-CoV-2 to gain a 3D cryo-EM structure of the ternary RBD-ACE2 complex. They observed a similar interface as that between SARS-CoV and ACE2, where an extended loop region of the RBD spans the arch-shaped α1 helix of the ACE2-PD like a bridge. Despite the similarity, SARS-CoV-2-RBD differs in various sequence variations and conformational deviations when interacting with ACE2. The effect of these changes on the new coronavirus’s ability to bind to the receptor and the infectivity need to be further studied and verified.
The paper Structural Basis for the Recognition of SARS-CoV-2 by Full-length Human ACE2 is on the Science Magazine website.
Author: Reina Qi Wan | Editor: Michael Sarazen
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