New route for SARS-CoV-2 entry

Researchers have found that binding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to host angiotensin converting enzyme 2 (ACE2) is essential for the virus to invade and infect host cells. Has been established for a long time.New research published in reputable journals Science Potential treatment of a second type of host transmembrane receptor called neuropilin that can attach to the SARS-CoV-2 spike protein and increase its infectivity in October 2020 The target value has been reported.

In this groundbreaking study, Professor Peter Cullen of the Department of Biochemistry, a research group in the Department of Life Sciences in Bristol. Associate Professor Yohei Yamauchi, virologist at the Faculty of Cellular and Molecular Medicine.

Dr. Boris Simonetti, a senior researcher at the Karen Institute, uses multiple approaches to promote viral infection by recognizing a protein called neuropilin-1 on the surface of human cells that SARS-CoV-2 uses. I found that.

Yohei, Boris and Pete explain: “Looking at the SARS-CoV-2 spike protein sequence, I was amazed at the presence of a small sequence of amino acids that appeared to mimic the protein sequence that interacts with human proteins. Neuropyrin-1.

This allowed us to propose a simple hypothesis. Can the SARS-CoV-2 spike protein bind to neuropilin-1 to help human cells infect the virus? Excitingly, by applying various structural and biochemical approaches, we were able to establish that the SARS-CoV-2 spike protein actually binds to neuropilin-1.

“Once we confirmed that the spike protein binds to neuropilin-1, we were able to show that the interaction helps enhance SARS-CoV-2 infiltration in human cells grown in cell culture.

This transmission electron microscope image shows SARS-CoV-2, a virus that causes COVID-19, isolated from a patient in the United States. Viral particles have been shown to emerge from the surface of cells cultured in the laboratory.The spikes on the outer edge of the virus particles Coronavirus Their name, like a crown. Colorized image captured at NIAID’s Rocky Mountain Laboratories (RML) in Hamilton, Montana. Credit: NIAID

Spike cutting site

The COVID-19 pandemic has caused a huge number of cases of over 42.9 million and has killed far more than 1 million worldwide to date. The viral agent SARS-CoV-2 enters the host cell via a spike protein that binds to the ACE2 receptor on the cell. The spike protein contains two subunits, S1 and S2, and has a polybasic furin cleavage site at the two interfaces. This allows the host cell’s proprotein convertase or furin to cleave the spike when it binds to the receptor.

The S1 and S2 subunits are still non-covalent, and S2 appears to be further primed by the serine protease TMPRSS2. Furin cleavage of the spike protein leads to increased viral infectivity. Flynn inhibition, or deletion of the multibasic RRAR site, reduces viral invasion.

Neuropilin factor

The S1 subunit has a C-terminal amino acid sequence that follows the C-terminal rule (CendR). This type of peptide attaches to neuropilin-1 (NRP1) and NRP2, which are transmembrane receptors that affect many diverse processes in the body. The current study aimed to investigate the relationship between the two.

The researchers used a GFP-labeled S1 construct expressed in ACE2-positive cells in culture. They found that the S1 protein bound to both ACE2 and NRP-1 in GFP-S1 cells, but not to GFP-S1ΔRRAR cells lacking the furin cleavage site. A similar degree of S1 binding was also observed with NRP2. Several bindings to the deletion mutant indicating that neuropilin interacted with S1 independently of the CendR residue were also observed.

Infectivity is reduced without NRP1

In cells lacking NRP1 but expressing ACE2, virus-wide attack was found to reduce infection levels. Cells lacking both were completely uninfected. In another cell assay, treatment with suppressor shRNA, which prevents NRP1 expression, reduced the level of viral infection again. In the absence of this protein, the virus can bind to the cell surface, but its internal translocation is halved. Therefore, NRP1 has been shown to be essential for viral invasion and cell infection. Their results also supported the existence of a CendR-independent mechanism of infection enhancement mediated by NRP1.

SARS-CoV-2 infection was significantly greater in NRP-positive cells, but no increase was observed in the presence of the T316R mutation, indicating that this change reduced the association between NRP1 and the S1 subunit. .. They found that monoclonal antibodies targeting the NRP1 protein bound to the CendR-binding pocket expressed on cells showed high specificity and reduced the ability of SARS-CoV-2 to infect cells. Incubation with soluble ACE2 also prevents SARS-CoV-2 infection, demonstrating the validity of previous findings.

The use of the small molecule NRP1 inhibitor EG00229 has also been shown to be able to effectively inhibit S1-NRP1 binding by binding to the b1CendR binding pocket of NRP1. Therefore, it presents a therapeutic target for reducing the infectivity of the virus in human cells.

How Neuropilin Increases Virus Infectivity

Spike priming with a host protease is performed prior to virus invasion. The CendR sequence generated by cleavage of the spike protein at the S1 / S2 interface binds to neuropilin on the cell surface. It is not essential for virus attachment to the cell surface, but it promotes virus invasion and cell infection.

Researchers do not know how neuropilin raises the level of viral infection. However, they may attribute this to the known ability of neuropilin to mediate macropinocytosis, allowing cells to swallow attached molecules and particles with large pockets of cell membranes and allow CendR-binding molecules to enter cells. It is assumed that there is.

Both NRP1 and NRP2 are known to be upregulated in lung tissue samples from COVID-19 patients. Therefore, the binding of NRP1 to the S1-CendR motif may be one of the reasons why SARS-CoV-2 is more infectious than SARS-CoV. It may be the target of future treatment for this disease.