High-resolution optical imaging in this study redefines the initial steps of SARS-CoV-2 entry. Instead of single-molecule binding to a unique receptor on the cell surface, the authors report that heparan sulfate (HS) clusters on the plasma membrane act as the primary docking sites that mediate viral attachment and trigger endocytosis. According to the abstract, ACE2 — widely considered the canonical entry receptor — operates downstream of HS and is required for subsequent viral genome expression rather than for the initial attachment event.
The investigators applied advanced light microscopy capable of resolving individual virions and receptors to study virus–cell interactions at near-molecular resolution. The abstract identifies MINFLUX nanoscopy as the technique used to visualize single virions and the receptor organization on the cell surface. This single-molecule–level imaging enabled direct observation of how SARS-CoV-2 engages the plasma membrane, revealing structural arrangements that conventional light microscopy cannot resolve.
Rather than interacting with isolated HS chains, SARS-CoV-2 binds to discrete HS-rich clusters that contain roughly 6 to 137 HS molecules. These clusters are notable for their vertical projection above the plasma membrane: individual clusters extend approximately 60–410 nm from the membrane surface. The clusters are spatially sparse, present at an approximate density of one cluster per 6 μm² of membrane. These tall, multivalent HS assemblies serve as docking platforms that concentrate viral particles and facilitate their subsequent internalization.
The data summarized in the abstract support a two-stage model of SARS-CoV-2 entry. In stage one, HS clusters on the cell surface mediate attachment and promote endocytosis of the virus. In stage two, ACE2 functions after entry initiation to enable viral genome expression within the host cell. Thus, ACE2 is characterized as downstream of HS in this paradigm: necessary for productive infection after HS-mediated attachment and uptake, but not the primary mediator of surface docking.
The authors tested pharmacologic inhibition of HS binding using the clinically used HS-binding agent pixantrone. According to the abstract, pixantrone strongly inhibited attachment and infection of human airway cells by an authentic SARS-CoV-2 Omicron JN.1 subvariant. This functional blockade supports the central role of HS interactions in the early steps of SARS-CoV-2 infection and demonstrates a potential repurposing strategy targeting HS–virus binding to prevent viral entry.
This work establishes a revised view of viral entry in which HS clusters act as key attachment and endocytosis mediators, with ACE2 acting further downstream to permit genome expression. Because many other viruses are known to bind HS — historically considered an attachment regulator rather than a bona fide receptor — the authors suggest that the paradigm identified for SARS-CoV-2 may extend to other viral pathogens. Targeting HS–virus interactions, for example with HS-binding compounds like pixantrone, is proposed as a viable anti-COVID-19 strategy and possibly as a broader antiviral approach.
The abstract discloses that two authors (Jessica Matthias and Christian A. Wurm) are employed by Abberior Instruments America LLC, a company that commercializes the MINFLUX microscope used in the study. Other listed authors declared no competing interests.
The PubMed abstract provides the study’s central observations and summary conclusions but does not include detailed experimental protocols, quantitative assay parameters, sample sizes, statistical analyses, or full methodological descriptions. These details were not reported in the abstract and would need to be obtained from the full published article for in-depth evaluation, reproduction of experiments, or critical appraisal of robustness.
Using single-molecule nanoscopy, the investigators identified tall, multimeric heparan sulfate clusters as discrete docking sites that mediate SARS-CoV-2 attachment and endocytosis, while ACE2 acts downstream to enable viral genome expression. Pharmacologic blockade of HS binding with pixantrone reduced attachment and infection by an authentic Omicron JN.1 subvariant in human airway cells, supporting HS interactions as a candidate antiviral target. The authors propose that this entry paradigm may have broader relevance for other HS-binding viruses.