Curtin University Researchers Discover That Gold, Copper, Silicon And Electric Fields Can Inhibit SARS-CoV-2
A new study by researchers from Curtin University-Australia has found that the spike proteins of the SARS-CoV-2 are susceptible to being trapped upon contact with gold, copper or silicon. The study team also found that applying electric fields can effectively destroy the spike proteins, which inhibits the virus.
Lead researcher, Dr Nadim Darwish from the School of Molecular and Life Sciences at Curtin University told Thailand Medical News
that the study findings showed that the spike proteins of coronaviruses attach to and become stuck on specific types of surfaces.
Dr Darwish explained, “Typically, coronaviruses have spike proteins on their periphery that allow them to penetrate host cells and cause infection and we have found these proteins becomes stuck to the surface of silicon, gold, and copper through a reaction that forms a strong chemical bond. We believe these materials can be used to capture coronaviruses by being used in air filters, as a coating for benches, tables, and walls, or in the fabric of wipe cloths and face masks. By capturing coronaviruses in these ways we would be preventing them from reaching and infecting more people.”
Dr Essam Dief, co-author and a Ph.D. candidate, also from the School of Molecular and Life Sciences at Curtin University said the study also found the coronavirus could be detected and destroyed using electrical pulses.
He said, “our study discovered that electric current can pass through the spike protein and because of this, the protein can be electrically detected. In the future, this finding can be translated to involve applying solution to a mouth or nose swab and testing it in a tiny electronic device able to electrically detect the proteins of the virus. This would provide instant, more sensitive, and accurate COVID testing.”
He further added, “Even more exciting, by applying electrical pulses, we found the spike protein’s structure is changed and at certain magnitude of the pulses, the protein is destroyed. Therefore, electric fields can potentially deactivate coronaviruses.”
Dr Darwish continued, “So, by incorporating materials such as copper or silicon in air filters, we can potentially capture and consequently stop the spread of the virus. Also, importantly, by incorporating electric fields through air filters, for example, we also expect this to deactivate the virus.”
The study findings were published in the peer reviewed journal: Chemical Science.
According to the study team, the structures of the spike proteins (S1 and S2) of most of the coronaviruses, including SARS-CoV-2, revealed that these proteins possess multiple disulfide (S–S) bonds. For example, the spike proteins (S1 and S2) of SARS-CoV-2 contain 14 S–S bonds in well-defined regions, with 10 S–S bridges in the S1 subunit. MERS-CoV contains 11 S–S bonds, and HCoV-229E spike protein contains 13 S–S bonds.
The SARS-CoV-2 spike protein S1 is composed of three domains, the receptor binding domain (RBD) that contains 4
S–S bridges, the N-terminal domain (NTD) that contains 3 S–S bridges and the S1/S2 cleavage site that contains 3 S–S bridges.
Such abundant S–S bridges indicate their important structural role in the formation and stabilization of the proper spike architecture and are likely to be present in future types of coronaviruses and their variants. For instance, SARS-CoV-2 spike protein RBD has an extra S–S bond as compared to SARS-CoV spike protein RBD.
In SARS-CoV-2, four pairs of S–S bridges (C336:C361, C379:C432, C391:C525, C480:C488) are found in the RBD. Among these four pairs, three are in the core, which help to stabilize the β sheet structure; the remaining S–S pair connects the loops in the distal end of the receptor-binding motif (RBM).
These S–S bonds are essential for the SARS-CoV-2 spike protein structure and its ability to infect, by interacting with the angiotensin-converting enzyme 2 (ACE2) human cell surface receptor via a thiol–disulfide exchange process.
On surfaces, S–S residues have been reported to form covalent bonding to noble metals such as Au and have been widely used in many applications. While these metal–organic molecule contacts are known to occur, the reaction mechanism is still debated.
In addition to metal surfaces, oxide-free silicon (Si–H), which is obtained by etching the native oxide away from the top layer of Si wafers, possesses a low reduction potential that allows for reducing chemical compounds and metal ions on its surface.
Recently, it has been demonstrated that Si–H surfaces can spontaneously reduce the S–S bonds in disulfide-terminated organic molecules and in the protein azurin that contains a peripheral S–S bond, enabling connecting these molecules to the Si surface via covalent S–Si bonds.
The study team used use surface spectroscopy, electrochemical and single-molecule scanning tunnelling break junction techniques to (i) study the chemical reactivity of SARS-CoV-2 with surfaces of electrodes, (ii) electrically detect the spike protein and (iii) study the effect of electric fields on spike proteins at the single-molecule level.
In summary, the study findings demonstrated that SARS-CoV-2 spike protein reacts and forms covalent bonds with specific metals and Si. Metal surfaces that have affinity to thiols/disulfides such as Au, Pt and Cu covalently bond to the spike protein via M–S bonding. Si surfaces also showed covalent Si–S bonding between the protein's S–S bonds and the surface, a process that is triggered by a spontaneous electrochemical reaction that involves partial oxidation of the Si surface and the reduction of disulfide bonds in the protein.
The rate of the reaction is two-fold higher on Si than on metals which is attributed to a slow homolytic cleavage of the S–S bonds in the spike protein when in contact with metals unlike the electrochemically initiated reaction on Si. In contrast, common surfaces such as plastic and stainless steel showed no covalent bonding between the protein and the surface, and the protein remains only physically adsorbed on these surfaces.
The spike protein was also shown to react efficiently with AuNPs with one order of magnitude higher S/Au ratio for AuNPs compared to flat Au surfaces. The capability of Si, Pt, Au and Cu to react with the spike protein can potentially be used to develop anti-coronavirus surfaces that are capable of irreversibly trapping the virus via strong covalent bonds. This covalent bonding potentially explains why SARS-CoV-2 survives a limited amount of time on copper compared to its viability on stainless steel and plastics.
The reaction of S–S in SARS-CoV-2 with metals and Si is particularly relevant because all previous and likely future coronaviruses will possess peripheral disulfide bonds in their spike proteins.
The study team concluded, “The study is exciting both fundamentally as it enables a better understanding of coronaviruses and from an applied perspective in helping to develop tools to fight the transmission of current and future coronaviruses.”
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