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

Study Background and Research Question

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for the global COVID-19 pandemic, invades host cells primarily via its spike protein, which interacts with multiple cell-surface receptors. While ACE2 is the canonical receptor, recent evidence points toward additional spike-binding partners, such as neuropilin-1 (NRP1) and the receptor tyrosine kinase AXL, especially in tissues with limited ACE2 expression. Given the centrality of the renin-angiotensin-aldosterone system (RAAS) in cardiovascular regulation and its established interplay with ACE2, the potential for angiotensin-derived peptides to modulate viral entry represents a compelling research frontier. The study by Oliveira et al. (2025) investigates whether various naturally occurring angiotensin peptides—including Angiotensin III (sequence: Arg-Val-Tyr-Ile-His-Pro-Phe)—can alter the binding affinity between the SARS-CoV-2 spike protein and its host cell receptors.

Key Innovation from the Reference Study

The primary innovation of this research lies in demonstrating that both C- and N-terminally truncated angiotensin peptides, not only the full-length Angiotensin II, significantly enhance SARS-CoV-2 spike protein binding to the AXL receptor. Notably, N-terminally truncated species such as Angiotensin III and IV display greater enhancement than Angiotensin II itself. This expands the mechanistic understanding of how RAAS peptides may influence viral entry, offering new avenues for therapeutic intervention and modeling COVID-19 susceptibility in the context of RAAS activity (Oliveira et al., 2025).

Methods and Experimental Design Insights

The researchers employed antibody-based binding assays to quantify the influence of various angiotensin peptides on the interaction between SARS-CoV-2 spike protein and its three major receptors: ACE2, NRP1, and AXL. The experimental design included systematic truncations of the angiotensin II sequence from both termini, as well as site-specific amino acid substitutions and modifications. Comparative analyses were performed using both longer (e.g., Angiotensin I) and shorter (e.g., Angiotensin IV) peptides. Specific attention was given to the Arg-Val-Tyr-Ile-His-Pro-Phe sequence of Angiotensin III, allowing direct examination of its effect on spike–AXL binding relative to other RAAS peptides.

The study also tested the impact of tyrosine modification at position 4, through both substitution and phosphorylation, to probe structural determinants of the observed enhancement. The use of well-controlled binding assays, including appropriate receptor and peptide controls, strengthens the validity of the findings.

Core Findings and Why They Matter

The reference study reports several critical discoveries:

• Angiotensin II increases spike–AXL binding by roughly two-fold, but has no effect on spike–ACE2 or spike–NRP1 binding.
• C-terminally truncated peptides (Angiotensin (1–7) and (1–6)) have a similar capacity to enhance spike–AXL binding as Angiotensin II.
• N-terminally truncated peptides, including Angiotensin III (2–8; Arg-Val-Tyr-Ile-His-Pro-Phe) and Angiotensin IV, display even stronger enhancement, with Angiotensin IV generating up to a 2.7-fold increase.
• Modifications at position 4 (tyrosine to valine substitution or tyrosine phosphorylation) further increase the spike–AXL interaction, emphasizing the importance of this residue for functional activity.
• Angiotensin IV, but not Angiotensin III, also enhances spike protein binding to ACE2 and NRP1, suggesting subtle distinctions in receptor modulation among angiotensin fragments.

These findings are significant because they suggest that the local peptide composition within the RAAS may influence viral entry pathways, particularly via the AXL receptor. This has broad implications for understanding COVID-19 pathogenesis in individuals with altered RAAS activity due to underlying cardiovascular or renal conditions, or as a result of pharmacological intervention.

Comparison with Existing Internal Articles

The mechanistic role of Angiotensin III in modulating RAAS signaling has been explored extensively in the context of cardiovascular and neuroendocrine research (internal article; internal article). Prior articles have characterized Angiotensin III as a potent pressor activity mediator and aldosterone secretion inducer, with dual affinity for AT1 and AT2 receptors—a role that underpins its utility in modeling RAAS-driven disease processes. However, the current reference study extends these insights by detailing the capacity of Angiotensin III and related peptides to modulate viral receptor interactions, bridging cardiovascular and infectious disease research. This cross-domain perspective is further contextualized in recent workflow discussions, which have highlighted the experimental utility of Angiotensin III for dissecting both classical RAAS functions and emerging roles in viral pathogenesis.

Why this cross-domain matters, maturity, and limitations

Bridging the domains of cardiovascular research and viral pathogenesis is crucial, as patient susceptibility to COVID-19 and disease severity are often intertwined with preexisting RAAS dysregulation. The demonstration that RAAS-derived peptides modulate SARS-CoV-2 spike–AXL binding suggests that the tissue-specific peptide milieu could influence viral entry and disease progression. Nevertheless, these findings are based on in vitro binding assays. The physiological relevance in vivo, including peptide concentrations, tissue distribution, and metabolic stability, remains to be established. Moreover, the study does not directly address downstream viral infection or replication, nor does it examine the therapeutic targeting of these peptide-receptor interactions. Thus, while the mechanistic insight is robust, translational application will require further validation.

Limitations and Transferability

Key limitations include the use of antibody-based binding rather than live-cell or in vivo models, and the lack of direct functional assays for viral entry or replication. The context of peptide concentrations and their physiological relevance in different tissue microenvironments is not fully addressed. Additionally, while the study identifies specific amino acid determinants (e.g., tyrosine at position 4) for enhanced spike–AXL binding, the broader landscape of post-translational modifications and peptide metabolism is not explored. These constraints should be considered when extrapolating findings to clinical or translational models.

Protocol Parameters

• Angiotensin peptide selection: Use peptides with defined C- and N-terminal truncations (e.g., Angiotensin III: Arg-Val-Tyr-Ile-His-Pro-Phe) to investigate receptor-binding enhancement.
• Binding assay setup: Employ antibody-based binding formats for quantifying spike–receptor interactions; ensure inclusion of negative and positive peptide controls.
• Modification analysis: When probing structure-function, include variants with targeted amino acid substitutions or phosphorylation at key residues (e.g., tyrosine at position 4).
• Peptide solubility: Prepare peptide stocks considering reported solubility limits (e.g., ≥23.2 mg/mL in water, ≥43.8 mg/mL in ethanol, ≥93.1 mg/mL in DMSO) as detailed in the product information.
• Storage conditions: Store peptides desiccated at –20°C and avoid long-term storage of solutions to preserve activity, as recommended by manufacturers.

Outlook

The discovery that Angiotensin III and related peptides can enhance SARS-CoV-2 spike–AXL binding introduces new mechanistic considerations for both cardiovascular and infectious disease research. This evidence supports the need for further studies evaluating the in vivo relevance of these interactions, and may inform strategies for therapeutic intervention targeting the intersection of RAAS activity and viral entry. Ongoing translational research will clarify the extent to which peptide-mediated modulation of spike–receptor binding influences clinical outcomes in COVID-19 and related pathologies.

Research Support Resources

For researchers seeking to replicate or expand on these findings, Angiotensin III (human, mouse) (SKU A1043) from APExBIO offers a high-purity, well-characterized cardiovascular research peptide with strong solubility and stability properties, suitable for advanced RAAS and receptor signaling studies. Its documented activity as an aldosterone secretion inducer and AT1/AT2 receptor ligand supports its use in both mechanistic and translational experimental workflows related to RAAS and emerging host-pathogen interactions.