Angiotensin Peptides and Their Role in SARS-CoV-2 Spike–AXL Interaction: Mechanistic Insights from Recent Research

Study Background and Research Question

The COVID-19 pandemic has driven intensive investigation into the molecular interactions that facilitate SARS-CoV-2 entry into host cells. While the angiotensin-converting enzyme 2 (ACE2) is recognized as the primary entry receptor, other molecules such as neuropilin-1 (NRP1) and AXL have emerged as alternative routes for viral attachment and infection, particularly in tissues with low ACE2 expression. The renin–angiotensin–aldosterone system (RAAS) peptides—including Angiotensin II and its truncated derivatives—have well-characterized roles in cardiovascular regulation, but their potential to modulate viral host-cell interactions remains underexplored. The central question addressed by Oliveira et al. (2025) is whether naturally occurring angiotensin peptides can alter the binding between the SARS-CoV-2 spike protein and its cellular receptors, with a special focus on AXL.

Key Innovation from the Reference Study

The principal innovation of this study is the systematic assessment of how naturally occurring angiotensin peptides, including specific sequence truncations such as Angiotensin III (sequence: Arg-Val-Tyr-Ile-His-Pro-Phe), modulate the binding of the SARS-CoV-2 spike protein to AXL. The work demonstrates that not only does Angiotensin II enhance spike–AXL interaction, but N-terminally truncated forms—especially Angiotensin III and Angiotensin IV—potentiate this effect further. This highlights a previously unrecognized interface between RAAS peptide signaling and viral receptor engagement, suggesting that endogenous peptide fluctuations could influence susceptibility or progression of COVID-19.

Methods and Experimental Design Insights

Oliveira et al. employed antibody-based binding assays to quantify the effects of various angiotensin peptides on the interaction between the SARS-CoV-2 spike protein and three cell-surface receptors: ACE2, NRP1, and AXL. Peptides tested included full-length Angiotensin I (1–10), Angiotensin II (1–8), Angiotensin III (2–8), Angiotensin IV (3–8), and shorter C-terminal/N-terminal truncations. The authors also introduced targeted amino acid substitutions and phosphorylation modifications to probe the role of specific residues, notably tyrosine at position 4 in the peptide sequence. Peptide-induced enhancements in spike–receptor binding were quantified relative to baseline (no peptide) controls.

• Binding assays were performed under controlled conditions to isolate specific peptide–receptor effects.
• Comparative analysis of sequence-specific truncations allowed the mapping of structure–activity relationships.
• Site-specific modifications (e.g., Tyr4 phosphorylation) were tested to elucidate mechanistic determinants.

Core Findings and Why They Matter

The study's main results demonstrate that:

• Angiotensin II increases spike–AXL binding by approximately two-fold, but does not significantly affect spike–ACE2 or spike–NRP1 binding (Oliveira et al., 2025).
• N-terminal truncations of Angiotensin II, generating Angiotensin III (2–8) and Angiotensin IV (3–8), further enhance spike–AXL binding, with Angiotensin IV yielding a 2.7-fold increase.
• C-terminal truncations (Angiotensin (1–7), Angiotensin (1–6)) retain or slightly enhance activity, but to a lesser degree than N-terminal truncations.
• Substitution or phosphorylation of Tyr4 leads to augmented spike–AXL binding, suggesting that tyrosine modifications are critical for this interaction.
• Among all tested peptides, those with N-terminal deletions (like Angiotensin III) are most potent in enhancing spike–AXL binding, while Angiotensin IV also increases spike binding to ACE2 and NRP1.

These findings suggest that angiotensin peptides, and particularly specific truncated forms such as Angiotensin III, could act as endogenous modulators of viral entry via AXL, potentially influencing the tissue distribution and pathogenicity of SARS-CoV-2. This presents a mechanistic rationale for investigating RAAS-targeted therapies in the context of COVID-19 and related viral diseases.

Comparison with Existing Internal Articles

Several internal resources provide complementary context for the use and mechanistic understanding of Angiotensin III:

• The article "Angiotensin Peptides Enhance SARS-CoV-2 Spike–AXL Binding" summarizes the implications of peptide-mediated modulation of spike–receptor interactions, echoing the findings of Oliveira et al. and emphasizing the potential role of truncated angiotensins in mediating COVID-19 pathogenesis.
• "Angiotensin III (human, mouse): Mechanistic Insights for Research" focuses on the role of Angiotensin III as a cardiovascular research peptide, highlighting its established actions as a pressor activity mediator and aldosterone secretion inducer via AT1 and AT2 receptor engagement. While this resource centers on cardiovascular and neuroendocrine models, the reference study extends these mechanistic insights to viral pathogenesis.
• For researchers aiming to translate these findings into experimental assays, "Optimizing Cardiovascular and Neuroendocrine Assays with Angiotensin III" provides protocol advice for leveraging validated RAAS peptides, supporting the rigor and reproducibility of studies in both classical and emerging contexts.

Collectively, these articles frame Angiotensin III as both a canonical AT1 and AT2 receptor ligand in cardiovascular research and as a potentially important modulator of viral spike–receptor interactions.

Limitations and Transferability

This study was conducted in vitro using antibody-based binding assays. While robust in demonstrating direct peptide effects on spike–receptor affinity, the physiological relevance of these findings in vivo remains to be established. Factors such as peptide concentration, tissue distribution, and the dynamic regulation of RAAS during infection may modulate these effects. Additionally, the precise contribution of these mechanisms to clinical COVID-19 outcomes is not yet clarified, and further animal or clinical studies will be required to validate these peptide–virus interactions under physiological conditions.

Why this cross-domain matters, maturity, and limitations

The connection between RAAS peptides and viral receptor binding exemplifies a novel cross-domain interface—one bridging cardiovascular peptide biology and infectious disease pathogenesis. This emerging area is still in its early stages: the in vitro enhancement of spike–AXL binding by Angiotensin III and related peptides, as shown by Oliveira et al., suggests a plausible mechanism but does not yet establish causation in vivo. The evidence indicates that ongoing fluctuations in endogenous peptides may alter tissue susceptibility to infection, yet translational maturity is limited by the lack of direct clinical correlation. Researchers should interpret these findings as hypothesis-generating, warranting further exploration but not yet constituting actionable clinical guidance.

Protocol Parameters

• Peptide concentration range: Literature-tested concentrations for angiotensin peptides in binding assays typically span 1–10 μM; optimization may be required for specific receptor targets.
• Sequence selection: For studies on spike–AXL interaction, use truncated forms such as Angiotensin III (Arg-Val-Tyr-Ile-His-Pro-Phe) to probe N-terminal deletion effects.
• Peptide solubility: Reference product information reports Angiotensin III is soluble at ≥23.2 mg/mL in water, ≥43.8 mg/mL in ethanol, and ≥93.1 mg/mL in DMSO, supporting flexible assay design.
• Storage recommendations: For optimal experimental reproducibility, store desiccated at -20°C and avoid long-term storage of peptide solutions.

Research Support Resources

To facilitate studies replicating or extending these findings, researchers can employ Angiotensin III (human, mouse) (SKU A1043), a high-purity, well-characterized RAAS peptide with validated pressor and receptor ligand functions. Its defined sequence (Arg-Val-Tyr-Ile-His-Pro-Phe), robust solubility profile, and quality control data make it suitable for both cardiovascular and peptide–receptor binding studies. For additional guidance on assay optimization and mechanistic application, see this protocol-focused article. APExBIO peptides are referenced for their quality in research workflows, but selection should always be tailored to specific experimental needs.