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Mutations in membrane-fusion subunit of spike glycoprotein play crucial role in the recent outbreak of COVID-19.

ABSTRACT: Coronavirus disease-2019 (COVID-19), the ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major threat to the entire human race. It is reported that SARS-CoV-2 seems to have relatively low pathogenicity and higher transmissibility than previously outbroke SARS-CoV. To explore the reason of the increased transmissibility of SARS-CoV-2 compared with SARS-CoV, we have performed a comparative analysis on the structural proteins (spike, envelope, membrane, and nucleoprotein) of two viruses. Our analysis revealed that extensive substitutions of hydrophobic to polar and charged amino acids in spike glycoproteins of SARS-CoV2 creates an intrinsically disordered region (IDR) at the beginning of membrane-fusion subunit and intrinsically disordered residues in fusion peptide. IDR provides a potential site for proteolysis by furin and enriched disordered residues facilitate prompt fusion of the SARS-CoV2 with host membrane by recruiting molecular recognition features. Here, we have hypothesized that mutation-driven accumulation of intrinsically disordered residues in spike glycoproteins play dual role in enhancing viral transmissibility than previous SARS-coronavirus. These analyses may help in epidemic surveillance and preventive measures against COVID-19.

SUBMITTER: Podder S

PROVIDER: S-EPMC7675664 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:A fusion protein expressed on the surface of enveloped viruses mediates fusion of the viral and cellular membranes to facilitate virus infection. Pre- and postfusion structures of viral fusion proteins have been characterized, but conformational changes between them remain poorly understood. Here, we examined the intermediate conformation of the murine coronavirus fusion protein, called the spike protein, which must be cleaved by a cellular protease following receptor binding. Western blot analysis of protease digestion products revealed that two subunits (67 and 69 kDa) are produced from a single spike protein (180 kDa). These two subunits were considered to be by-products derived from conformational changes and were useful for probing the intermediate conformation of the spike protein. Interaction with a heptad repeat (HR) peptide revealed that these subunits adopt packed and unpacked conformations, respectively, and two-dimensional electrophoresis revealed a trimeric assembly. Based on biochemical observations, we propose an asymmetric trimer model for the intermediate structure of the spike protein. Receptor binding induces the membrane-binding potential of the trimer, in which at least one HR motif forms a packed-hairpin structure, while membrane fusion subunits are covered by the receptor-binding subunit, thereby preventing the spike protein from forming the typical homotrimeric prehairpin structure predicted by the current model of class I viral fusion protein. Subsequent proteolysis induces simultaneous packing of the remaining unpacked HRs upon assembly of three HRs at the central axis to generate a six-helix bundle. Our model proposes a key mechanism for membrane fusion of enveloped viruses.IMPORTANCE Recent studies using single-particle cryo-electron microscopy (cryoEM) revealed the mechanism underlying activation of viral fusion protein at the priming stage. However, characterizing the subsequent triggering stage underpinning transition from pre- to postfusion structures is difficult because single-particle cryoEM excludes unstable structures that appear as heterogeneous shapes. Therefore, population-based biochemical analysis is needed to capture features of unstable proteins. Here, we analyzed protease digestion products of a coronavirus fusion protein during activation; their sizes appear to be affected directly by the conformational state. We propose a model for the viral fusion protein in the intermediate state, which involves a compact structure and conformational changes that overcome steric hindrance within the three fusion protein subunits.

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Mutations in membrane-fusion subunit of spike glycoprotein play crucial role in the recent outbreak of COVID-19.

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