Andes Hantavirus Receptor Structure Mapped

For the first time, scientists have watched, in atomic detail, how one of the world’s deadliest rodent-borne viruses grabs hold of a human cell. In a study published on 21 October in Nature, a team led by groups at Albert Einstein College of Medicine, the Institut Pasteur and LSU Health Shreveport describe the structure of the Andes virus (ANDV) spike locked onto its receptor, a cell-surface protein called protocadherin-1 (PCDH1).

The picture answers a question that had been open since the same labs identified PCDH1 as the Andes virus doorway eight years ago: not just which protein the virus uses, but exactly how it grips it. “Our latest work solves this puzzle,” said co-corresponding author Kartik Chandran of Einstein in the college’s announcement. “We reveal a new way in which a virus can capture its receptor during infection and also suggest how we can fight back.”

In brief

Researchers have solved the structure of the Andes hantavirus spike gripping its human receptor, PCDH1, and found a single receptor wedged into a deep pocket formed by four protein units.
The pocket is too narrow for most antibodies, which helps explain how the virus hides its vulnerable spot; the authors say it also shows where to aim future drugs.
There is still no approved vaccine or treatment for Andes virus, and this is basic research, not a therapy.

One receptor, wedged into a four-part spike

Most viruses present a receptor-binding site on each unit of their spike. The Andes virus does something stranger. Its spike is four identical glycoprotein units locked into a square, and the receptor does not dock onto any single unit. Instead, as the paper puts it, PCDH1 “asymmetrically engages a deep central pocket formed by four Gn protomers in the spike”. A single receptor molecule reaches into the very centre of the assembled spike and touches all four units at once.

That explains an old laboratory puzzle: PCDH1 binds to whole virus particles and to intact soluble spikes, but not to single spike subunits. The binding site only exists once the four units come together. The authors call this a binding mode that, to their knowledge, “has not been observed in any enveloped virus”.

Seeing it at all took a trick from protein design. The soluble spike kept falling apart in the test tube, so the team fused the spike to HALC4_136, a de novo tetramerisation domain, to hold the square together. Both the paper and Einstein describe it as “an artificial intelligence-designed scaffold” — the kind of made-to-order protein part that TSN has covered in work on open protein-design models and on enzymes designed from scratch at the Baker Lab. With the spike stabilised, cryo-electron microscopy resolved the structure to near-atomic detail (2.4-2.6 Angstrom).

A pocket that keeps antibodies out

The central pocket is roughly 2.5 nanometres across and about 2.1 nanometres deep — wide enough for PCDH1’s slim tip, but far too small for a conventional antibody fragment, which is several times larger. “PCDH1’s long, slender shape lets it reach deep inside, but most antibodies are too bulky to follow,” said Rohit Jangra of LSU Health Shreveport.

The team then looked at four human antibodies known to block infection. They fell into two camps. As the paper reports, the antibodies “block receptor binding through two distinct mechanisms — occluding access to the PCDH1-binding site or sterically preventing receptor engagement”. In plain terms, some sit right over the mouth of the pocket, while others jam the approach from the side using their bulky stems rather than reaching in.

Chandran framed the escape problem the virus has evolved: the virus can mutate to shrug off antibodies without losing its grip on the receptor, which he called “a kind of molecular ‘friend-or-foe’ identification system”. The conserved residues the virus truly depends on sit at the bottom of a cleft that ordinary antibodies cannot reach.

Why a structure is not yet a cure

The practical pay-off is a blueprint, not a medicine. The authors are explicit that their findings “provide a framework for the design of antiviral therapeutics targeting the hantavirus spike” — a framework, not a drug. There is no candidate compound, no animal efficacy study of a new therapy and no human trial in this paper. As the paper states flatly, “no US Food and Drug Administration (FDA)- or European Medicines Agency (EMA)-approved medical countermeasures are available to prevent or treat hantaviral infections”.

What the structure does is tell chemists where to aim. Because the useful target is a narrow, deep pocket, the obvious route is not a standard antibody but something “long and skinny” — a small molecule, a single-domain antibody, or an engineered binder that can slide to the bottom of the cleft. That is the same design problem now being attacked with computational tools, including efforts to design binders against toxins. Turning any of that into a tested treatment would take years of work the paper does not claim to have done.

The stakes are high enough to justify the effort. Andes virus causes hantavirus cardiopulmonary syndrome, with case-fatality rates the paper says “can approach 40%”, and it is the one hantavirus known to pass from person to person. Einstein notes that this year an outbreak on a cruise ship “killed three passengers and sickened 13”, a reminder of how little clinicians currently have to offer. For UK readers the link is mainly scientific: University College London’s Gorka Lasso is among the paper’s co-authors, and related Old World hantaviruses circulate in Europe.

The next thing to watch is whether any group can turn the “find a pocket, block it” idea into a real molecule that works in animals — the step between an elegant structure and a drug that could change outcomes in an outbreak.