N501Y mutation in SARS-CoV-2 responsible for increased viral transmission

Researchers at the University of Texas, USA, have confirmed the specific mutation in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variant B.1.1.7, the causative agent of coronavirus 2019 (COVID-19), allowed it to be more transmissible than the ancestral strain. The N501Y substitution is one of the 8 leading protein substitutions present in the British variant and also appeared convergently in the Brazilian (P.1) and South African (B.1.351) variants.

The Menachery Lab, in collaboration with the Shi Lab, used a combination of reverse genetics and experimentation in hamsters and human airway epithelial cells to study the impact of cutting edge mutations present in B.1.1.7. They were able to rule out seven of the surrogate mutants as true viral health factors, highlighting the N501Y mutation as the only “mutation of concern”.

This research confirms what other studies have found, namely that the N501Y mutation is what allows the variant to be more transmissible, by allowing the virus to bind more easily to ACE receptors. human angiotensin 2 (ACE2). ACE2 is an enzyme found on the membranes of human heart, kidney and lung cells and, if compromised, can increase the host range, transmission, and pathogenesis of a virus.

A pre-printed version of the research paper is available for full reading on the bioRxiv*server.

The research

Scott Weaver and his colleagues infected Syrian hamsters with SARS-CoV-2 mutants. The mutant variants consisted of several strains, each of which had only one of the individual tip substitutions present in variant B.1.1.7, as well as one variant containing all eight mutations.

The hamsters were removed after a period of 4 days after infection, washed through the nose and necropsied. The animals were cohabited with uninfected hamsters one day after the initial infection for 8 hours.

During the analysis, the researchers were able to reduce and isolate N501Y as the only consistent and significant major substitution to affect viral health, replicating faster in the nasal airways and lung cavities of hamsters. They found that this mutation did not affect virulence, only the rate of transmission.

Finally, the researchers performed binding assays using the recombinant spike receptor binding domain (RBD) and human ACE2 proteins, suspecting that the change from asparagine to tyrosine in the N501Y mutation was what allowed further development. high binding affinity to the ACE2 receptor. Their results suggest that the N501Y mutation improves the viral ability for viral replication in the upper airways.

The construction of mutants and their plaque morphologies. a, The design of the reverse genetic construct of all individual and combined mutations on the wt D614G backbone. The numbers on the top genomic map refer to open reading frames (ORFs). E, envelope glycoprotein gene; L, lead sequence; M, membrane glycoprotein gene; N, core gene; UTR, untranslated region. b, the location of all 8 UK B.1.1.7 and D614G substitutions on the trimer of the SARS-CoV-2 spike protein. c, The morphologies of all rescued SARS-CoV-2 mutant variants. Plates were stained 2.5 days after infection of Vero E6 cells.

Go forward

At present, the British variant strain is still susceptible to being neutralized by current vaccines. However, its increased transmissibility may allow resistant mutants to appear more quickly. The authors note that only two of the eight peak mutations conferred fitness benefits for the virus in terms of infection and transmissibility – the N501Y substitution and Δ69-70 codon deletion (also convergent in the Brazil and L variants. ‘South Africa, although variably effective). They caution, therefore, that the other six should be investigated to understand their roles in Alternative B.1.1.7. They also recognize that ideally the primate or human models would generate more relevant results than the hamsters used in the study, however, these were the best rodent models available.

The total number of global cases of republished SARS-CoV-2 infections is currently over 118.4 million. Variant B.1.1.7 has so far been reported in at least 25 countries and the number of cases is increasing.

By improving our understanding of the virus and its variants and the roles their mutations play, researchers can better combat its spread and virulence.

*Important Notice

bioRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behaviors, or treated as established information.