A Short Stapled Peptide Designed to Block SARS-CoV-2 From Entering Human Cells | Research

The takeaway

Researchers created a compact 9-amino-acid stapled peptide that can compete with the ACE2 receptor to block the SARS-CoV-2 spike protein, offering a potential new antiviral strategy.

9 amino acids
The length of the stapled peptide that competes with the much larger ACE2 receptor for spike protein binding

What the researchers found

A 9-amino-acid peptide (sequence HEAEDLFYQ, residues 34–42 of ACE2 α-helix 1) was chemically stapled using ring-closing metathesis at the i to i+4 positions. This stapled peptide competed with recombinant ACE2 for binding to the SARS-CoV-2 Spike receptor-binding domain (RBD) at micromolar concentrations in a colorimetric ELISA assay.

Circular dichroism studies confirmed the ring-closing metathesis staple stabilized the helical structure more effectively than an alternative triazole staple produced by click chemistry. Molecular dynamics simulations further showed the stapled peptide not only bound the Spike RBD and sterically interfered with ACE2 binding, but displayed higher affinity for the target than the unstapled parent epitope.

Why it matters

Most COVID-19 treatments target the virus after it has already entered cells. A peptide that blocks the spike protein from grabbing ACE2 could stop infection at the very first step — viral entry. Because the peptide is small (only 9 amino acids), it could be easier to manufacture and potentially deliver as an inhaled or nasal treatment, offering an alternative to large antibody-based therapies.

How the study worked

The researchers synthesized a series of peptide derivatives based on a short segment of the ACE2 receptor's first alpha-helix. They used two different chemical stapling approaches — ring-closing metathesis and click chemistry (triazole) — to lock the peptides into their helical shape. Binding to the SARS-CoV-2 spike protein was tested using a colorimetric ELISA screening assay, and the peptides' structures were analyzed with circular dichroism spectroscopy. Molecular dynamics (MD) simulations were run to model how the stapled peptide interacts with the spike protein's receptor-binding domain.

What this study cannot tell us

All experiments were conducted in vitro using purified proteins and computer simulations — no cell-based infection assays or animal studies were reported. The binding affinity was in the micromolar range, which is relatively modest compared to therapeutic antibodies. The peptide's stability in biological fluids, its ability to reach target tissues, and any potential off-target effects remain unknown. Results with isolated spike RBD may not fully reflect the behavior of the trimeric spike on intact virus particles.

How to read the evidence

This is an early-stage in vitro and computational study with no cell-based or animal data. While the biochemical and structural results are promising, the findings have not been validated in living systems, placing this at a preclinical/exploratory evidence level.

When this study was published

Published in 2023, this study addressed SARS-CoV-2 entry inhibition. While the pandemic context has evolved, the stapled peptide design principles and protein-protein interaction disruption strategies remain relevant to ongoing antiviral research.

The bigger picture

Stapled peptides are an emerging class of therapeutics that combine the specificity of biologics with the stability advantages of small molecules. This work adds to a growing body of research exploring peptide-based viral entry inhibitors as alternatives to monoclonal antibodies, which are expensive and can lose effectiveness against new variants. The approach of mimicking host receptor fragments to competitively block pathogen binding could be applied beyond COVID-19 to other viruses that use similar entry mechanisms.

Questions still open

Can this stapled peptide actually prevent SARS-CoV-2 from infecting living cells, not just bind the spike protein in a test tube?
Would the peptide retain its blocking activity against newer spike protein variants with mutations in the RBD?
Could this peptide be delivered intranasally to act directly at the site of viral entry in the respiratory tract?

Common questions

What is a stapled peptide and why does it matter here?

A stapled peptide is a short protein fragment that has been chemically modified with a molecular 'staple' to lock it into a specific 3D shape — in this case, a helix. This is important because peptides in solution tend to be floppy and lose their shape, which weakens their ability to bind targets. By stapling the peptide, the researchers made it hold the same helical shape it would have as part of the full ACE2 protein, improving its ability to block the spike protein.

Could this peptide be used as a COVID-19 treatment?

Not yet. This study demonstrated that the stapled peptide can bind to the SARS-CoV-2 spike protein in laboratory conditions, but it has not been tested in cells, animals, or humans. Significant further research would be needed to determine whether it could work as an actual antiviral drug, including testing its stability in the body, its ability to prevent real viral infections, and its safety profile.

Read the original research

Identification of a short ACE2-derived stapled peptide targeting the SARS-CoV-2 spike protein.

European journal of medicinal chemistry, 249, 115118

View on PubMed ↗Publisher’s paper ↗

Citation

Calugi, Lorenzo; Sautariello, Giulia; Lenci, Elena; Mattei, Mauro Leucio; Coppa, Crescenzo; Cini, Nicoletta; Contini, Alessandro; Trabocchi, Andrea. (2023). Identification of a short ACE2-derived stapled peptide targeting the SARS-CoV-2 spike protein.. European journal of medicinal chemistry, 249, 115118. https://doi.org/10.1016/j.ejmech.2023.115118