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Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme.

ABSTRACT: Coronavirus 3′-to-5′ exoribonuclease (ExoN), residing in the nonstructural protein (nsp) 10–nsp14 complex, boosts replication fidelity by proofreading RNA synthesis and is critical for the virus life cycle. ExoN also recognizes and excises nucleotide analog inhibitors incorporated into the nascent RNA, undermining the effectiveness of nucleotide analog–based antivirals. Here we present cryo–electron microscopy structures of both wild-type and mutant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nsp10-nsp14 in complex with an RNA substrate bearing a 3′-end mismatch at resolutions ranging from 2.5 to 3.9 angstroms. The structures reveal the molecular determinants of ExoN substrate specificity and offer insight into the molecular mechanisms of mismatch correction during coronavirus RNA synthesis. Our findings provide guidance for rational design of improved anticoronavirus therapies.

SUBMITTER: Liu C

PROVIDER: S-EPMC9836006 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme.

Liu Chang C Shi Wei W Becker Scott T ST Schatz David G DG Liu Bin B Yang Yang Y

Science (New York, N.Y.) 20210727 6559

Coronavirus 3′-to-5′ exoribonuclease (ExoN), residing in the nonstructural protein (nsp) 10–nsp14 complex, boosts replication fidelity by proofreading RNA synthesis and is critical for the virus life cycle. ExoN also recognizes and excises nucleotide analog inhibitors incorporated into the nascent RNA, undermining the effectiveness of nucleotide analog–based antivirals. Here we present cryo–electron microscopy structures of both wild-type and mutant severe acute respiratory syndrome coronavirus ...[more]

PMID: 34315827

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Project description:The highly contagious and fast-spreading omicron variant of SARS-CoV-2 infects the respiratory tracts efficiently. The receptor-binding domain (RBD) of the omicron spike protein recognizes human angiotensin-converting enzyme 2 (ACE2) as its receptor and plays a critical role in the tissue tropism of SARS-CoV-2. Here, we showed that the omicron RBD (strain BA.1) binds to ACE2 more strongly than does the prototypic RBD from the original Wuhan strain. We also measured how individual omicron mutations affect ACE2 binding. We further determined the crystal structure of the omicron RBD (engineered to facilitate crystallization) complexed with ACE2 at 2.6 Å. The structure shows that omicron mutations caused significant structural rearrangements of two mutational hot spots at the RBD/ACE2 interface, elucidating how each omicron mutation affects ACE2 binding. The enhanced ACE2 binding by the omicron RBD may facilitate the omicron variant's infection of the respiratory tracts where ACE2 expression level is low. Our study provides insights into the receptor recognition and tissue tropism of the omicron variant. IMPORTANCE Despite the scarcity of the SARS-CoV-2 receptor-human angiotensin-converting enzyme 2 (ACE2)-in the respiratory tract, the omicron variant efficiently infects the respiratory tract, causing rapid and widespread infections of COVID-19. The omicron variant contains extensive mutations in the receptor-binding domain (RBD) of its spike protein that recognizes human ACE2. Here, using a combination of biochemical and X-ray crystallographic approaches, we showed that the omicron RBD binds to ACE2 with enhanced affinity and also elucidated the role of each of the omicron mutations in ACE2 binding. The enhanced ACE2 binding by the omicron RBD may contribute to the omicron variant's new viral tropism in the respiratory tract despite the low level of ACE2 expression in the tissue. These findings help us to understand tissue tropism of the omicron variant and shed light on the molecular evolution of SARS-CoV-2.

Dataset Information

Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme.

Publications

Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme.

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