Angiotensin Peptides Enhance SARS-CoV-2 Spike–AXL Binding: Mechanistic Insights for RAAS and Viral Pathogenesis

Study Background and Research Question

The renin–angiotensin–aldosterone system (RAAS) plays a central role in cardiovascular regulation and homeostasis, with angiotensin peptides acting as key effectors. The emergence of COVID-19, caused by SARS-CoV-2, has renewed interest in the interplay between RAAS and viral pathogenesis due to the virus’s utilization of angiotensin-converting enzyme 2 (ACE2) as an entry receptor. However, alternative viral entry routes, such as via the receptor tyrosine kinase AXL, are increasingly recognized, especially in tissues with low ACE2 expression. The study by Oliveira et al. (Int. J. Mol. Sci. 2025, 26, 6067) investigates whether endogenous angiotensin peptides modulate the binding affinity of the SARS-CoV-2 spike protein to its host cell receptors—AXL, ACE2, and neuropilin-1 (NRP1).

Key Innovation from the Reference Study

The pivotal advance of this work is the demonstration that truncated angiotensin peptides, including Angiotensin III (sequence: Arg-Val-Tyr-Ile-His-Pro-Phe), can enhance the binding of the SARS-CoV-2 spike protein to the AXL receptor. Notably, N-terminally truncated peptides (such as Angiotensin III and Angiotensin IV) exhibited even greater potentiation of spike–AXL interactions than their precursor, Angiotensin II. The study further identifies specific amino acid modifications—such as tyrosine substitution or phosphorylation—that amplify this effect. These findings expand the conceptual framework for understanding how host peptide signaling may influence viral entry and COVID-19 severity.

Methods and Experimental Design Insights

Oliveira et al. employed antibody-based binding assays to quantify interactions between the SARS-CoV-2 spike protein and its known receptors (AXL, ACE2, NRP1) in the presence of various angiotensin peptides. The researchers systematically evaluated the effects of C-terminal and N-terminal deletions from Angiotensin II, as well as specific point modifications. The critical comparison involved evaluating the enhancement of spike–AXL binding by Angiotensin II, its truncated derivatives (including Angiotensin III and IV), and modified peptides. Additionally, the study assessed whether these peptides affected spike binding to ACE2 or NRP1, thereby delineating receptor specificity.

Core Findings and Why They Matter

• Angiotensin II increased spike–AXL binding two-fold, while Angiotensin I had no such effect (reference study).
• C-terminally truncated peptides (Angiotensin 1–7, 1–6) maintained spike–AXL enhancement similar to Angiotensin II.
• N-terminal truncations (Angiotensin III [2–8], IV [3–8]) and further truncated forms (Angiotensin 2–7, 5–7) showed a more pronounced effect, with Angiotensin IV causing a 2.7-fold increase in spike–AXL binding.
• Substitution of tyrosine at position 4, either by valine or by phosphorylation, further increased spike–AXL binding, highlighting the importance of this residue in modulating peptide–receptor interactions.
• Angiotensin IV, but not Angiotensin II or III, also enhanced spike binding to ACE2 and NRP1, suggesting some peptide-specific differences in receptor engagement.

These results suggest that the circulating pool of angiotensin peptides, particularly shorter forms such as Angiotensin III, may act as pressor activity mediators and influence viral entry via the AXL pathway. This mechanistic link could partly explain the observed association between RAAS dysfunction and COVID-19 severity, especially in individuals with cardiovascular comorbidities.

Comparison with Existing Internal Articles

Several recent reviews and technical reports support and contextualize these findings. For example, the article "Angiotensin Peptides Enhance SARS-CoV-2 Spike–AXL Binding" emphasizes the contribution of truncated angiotensin peptides to viral entry via non-canonical receptors, reinforcing the cross-talk between RAAS and COVID-19 pathogenesis.
Similarly, "Angiotensin III (human, mouse): Novel Insights into RAAS..." explores the role of Angiotensin III as a versatile AT1 and AT2 receptor ligand and its potential in disease modeling, including in infectious contexts.
The article "Angiotensin III: A Versatile Cardiovascular Research Peptide" highlights Angiotensin III's robust solubility and pressor/aldosterone-inducing properties, essential for both cardiovascular and viral research workflows.

Limitations and Transferability

While the reference study provides compelling biochemical evidence for angiotensin peptide-mediated enhancement of spike–AXL binding, several caveats remain. The findings were derived from in vitro binding assays, which may not fully recapitulate the complex in vivo dynamics of peptide concentrations, receptor expression, or cellular context. Furthermore, while Angiotensin III and related peptides show clear activity as aldosterone secretion inducers and cardiovascular research peptides, their contribution to actual SARS-CoV-2 infectivity and COVID-19 progression in humans will require direct validation in animal models or clinical cohorts. Finally, although the study suggests potential therapeutic targeting of peptide–receptor interactions, off-target effects and the broader impact on RAAS homeostasis must be considered.

Why this cross-domain matters, maturity, and limitations

The demonstration that endogenous RAAS peptides can modulate viral spike protein–host receptor interactions bridges cardiovascular and infectious disease domains. This cross-domain insight is particularly relevant for understanding why patients with underlying hypertension or altered RAAS activity may be at increased risk for severe COVID-19. However, the translational maturity of these findings is limited at present; further studies are needed to clarify in vivo relevance, and whether targeting angiotensin peptide pathways could become a viable intervention strategy.

Protocol Parameters

• Peptide selection: Use Angiotensin III (sequence Arg-Val-Tyr-Ile-His-Pro-Phe) as an N-terminally truncated derivative for enhanced spike–AXL binding studies.
• Concentration ranges: Follow binding assay conditions as outlined in the reference paper; typically, peptide concentrations in the low micromolar range were sufficient to observe effects.
• Buffer conditions: Maintain physiological ionic strength to preserve receptor–ligand affinities.
• Solubility considerations: Angiotensin III exhibits high solubility in water (≥23.2 mg/mL), ethanol (≥43.8 mg/mL), and DMSO (≥93.1 mg/mL), facilitating a range of experimental setups.
• Storage: For optimal stability, store peptide desiccated at -20°C; avoid long-term storage of solutions.
• Workflow recommendations: When modeling RAAS–viral interface in cardiovascular or pulmonary cell lines, consider parallel controls with Angiotensin II, III, and IV to delineate peptide-specific effects.

Research Support Resources

For researchers seeking to reproduce or extend these findings, Angiotensin III (human, mouse) (SKU A1043) offers a high-purity, well-characterized reagent suitable for both cardiovascular and viral pathogenesis workflows. This formulation supports precise modeling of peptide–receptor interactions due to its robust solubility and confirmed sequence (Arg-Val-Tyr-Ile-His-Pro-Phe). Quality control is ensured through HPLC and mass spectrometry analyses as detailed on the product page. For in-depth mechanistic discussions and protocol parameters, internal reviews such as "Angiotensin III (human, mouse): Mechanistic Insights and Translational Protocols" may provide additional guidance for cross-domain experimental design.