Emerging of a SARS-CoV-2 viral strain with a deletion in nsp1

Abstract

Background: The new Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), which was first detected in Wuhan (China) in December of 2019 is responsible for the current global pandemic. Phylogenetic analysis revealed that it is similar to other betacoronaviruses, such as SARS-CoV and Middle-Eastern Respiratory Syndrome, MERS-CoV. Its genome is ∼ 30 kb in length and contains two large overlapping polyproteins, ORF1a and ORF1ab that encode for several structural and non-structural proteins. The non-structural protein 1 (nsp1) is arguably the most important pathogenic determinant, and previous studies on SARS-CoV indicate that it is both involved in viral replication and hampering the innate immune system response. Detailed experiments of site-specific mutagenesis and in vitro reconstitution studies determined that the mechanisms of action are mediated by (a) the presence of specific amino acid residues of nsp1 and (b) the interaction between the protein and the host's small ribosomal unit. In fact, substitution of certain amino acids resulted in reduction of its negative effects.

Methods: A total of 17,928 genome sequences were obtained from the GISAID database (December 2019 to July 2020) from patients infected by SARS-CoV-2 from different areas around the world. Genomes alignment was performed using MAFFT (REFF) and the nsp1 genomic regions were identified using BioEdit and verified using BLAST. Nsp1 protein of SARS-CoV-2 with and without deletion have been subsequently modelled using I-TASSER.

Results: We identified SARS-CoV-2 genome sequences, from several Countries, carrying a previously unknown deletion of 9 nucleotides in position 686-694, corresponding to the AA position 241-243 (KSF). This deletion was found in different geographical areas. Structural prediction modelling suggests an effect on the C-terminal tail structure.

Conclusions: Modelling analysis of a newly identified deletion of 3 amino acids (KSF) of SARS-CoV-2 nsp1 suggests that this deletion could affect the structure of the C-terminal region of the protein, important for regulation of viral replication and negative effect on host's gene expression. In addition, substitution of the two amino acids (KS) from nsp1 of SARS-CoV was previously reported to revert loss of interferon-alpha expression. The deletion that we describe indicates that SARS-CoV-2 is undergoing profound genomic changes. It is important to: (i) confirm the spreading of this particular viral strain, and potentially of strains with other deletions in the nsp1 protein, both in the population of asymptomatic and pauci-symptomatic subjects, and (ii) correlate these changes in nsp1 with potential decreased viral pathogenicity.

Keywords: COVID-19; Deletion; Pathogenic; SARS-CoV-2; Viral adaptation; nsp1.

Fig. 1

Nsp1 alignment between sequences from SARS-CoV-2 wild type and strains carrying the KSF deletion. The amino acid sequences of SARS-CoV-2 wild type (WT) and SARS-CoV-2 with the 3 amino acids deletion (DEL) were aligned using Clustal Omega. The deletion is shown

Fig. 2

Comparison of NSP1 SARS-CoV and SARS-CoV-2. Comparison of core structure with prediction models of full length nsp1 SARS-CoV (cyan) and SARS-CoV-2 are superimposed in different colors (magenta and light pink). The prediction models for both C-terminal tails of nsp1 SARS-CoV with KSY (blue) and nsp1-SARS-CoV-2 with KSF present (blue) and KSF deleted (green) are predicted to be highly disordered compared with nsp1 Core elements (yellow). R.M.S.D is 0.78Å for core elements. Note that the core structure has been previously resolved for SARS -CoV (PDB code 2GDT), while the C-tail structure has not