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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Two studies published in Science in October 2010 examined how influenza A’s M2 protein conducts protons and opens in acidic conditions. Both put the channel’s histidine residues at the center of the process, but they differed over how essential a nearby tryptophan is. The work advanced a structural model of viral entry; it did not announce a new flu medicine.
What M2 does during influenza A entry
M2 is a proton channel embedded in the influenza A virus membrane. When a virus particle enters a host cell, it is enclosed in an endosome, whose interior becomes acidic. M2 allows protons to move into the virus, helping acidify its interior and promote the disassembly that releases the viral genome. That role also makes M2 a target for antiviral research. Chemistry World’s 2010 report and a later structural review describe this entry mechanism.
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The channel is made of four protein subunits, or a tetramer. In its transmembrane region, the amino acid histidine—specifically residue His37—helps sense acidity and participates in proton transfer. The 2010 research sought to explain how changes in acidity affect the channel’s structure and how protons move through it. The proposed routes are mechanistic interpretations of experimental measurements and structural models, not direct recordings of every proton handoff.
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| Study | Experimental system | What it proposed | Interpretive limit |
|---|---|---|---|
| Hu, Luo, and Hong, “Mechanisms of Proton Conduction and Gating in Influenza M2 Proton Channels from Solid-State NMR” | Solid-state NMR of His37 in a cholesterol-containing membrane designed to mimic the viral envelope; the study focused on a shorter protein segment. | A high-pH closed configuration and a low-pH conducting configuration. The authors proposed that His37 imidazole rings shuttle protons dynamically, with ring-flip-assisted deprotonation as a rate-limiting step. | The mechanism is the authors’ interpretation of NMR measurements; the experiment does not directly observe each proton transfer. |
| Sharma, Yi, Dong, and colleagues, “Insight into the Mechanism of the Influenza A Proton Channel from a Structure in a Lipid Bilayer” | A larger protein construct, lipid-bilayer structural data, and simulations. | A more detailed proposed proton-transfer pathway involving water, His37, and Trp41. | The tryptophan’s role was disputed, and simulations contribute to the proposed pathway rather than establishing every transfer step experimentally. |
The studies appeared back-to-back in Science on October 22, 2010: Hu, Luo, and Hong and Sharma and colleagues. Their different choices of construct and membrane system shaped what each could measure and infer.
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Why His37 was central—and Trp41 controversial
The Iowa State team’s NMR-focused interpretation assigned His37 a dynamic role: its imidazole rings were proposed to accept and pass protons, with ring flipping helping release a proton at a rate-limiting point. The Florida State team used its larger construct and simulations to develop a more elaborate pathway through water, His37, and Trp41. Both accounts made histidine central, but they did not agree on how necessary tryptophan was to the transfer mechanism.
Florida State researcher Huan-Xiang Zhou argued for a substantial role for tryptophan: “I think the tryptophan is actually a very integral part of this mechanism and I think not having the involvement of a tryptophan is too simplistic.” Iowa State researcher Mei Hong emphasized the value of direct measurement: “I would say that the direct experimental result is more trustworthy.” These comments reflect the researchers’ differing interpretations, not a settled resolution of the mechanism. As University of Oxford researcher Jason Schnell put it: “I like the construct that the Florida group used but I like the experiments that the Iowa group used.”
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What the membrane systems could—and could not—show
Studying M2 in a lipid bilayer can better approximate the environment of a viral membrane than studying it in detergent. But the contemporary report noted a tradeoff: the particular bilayer experiments had lower resolution than some earlier detergent-based structural studies. That is a qualification about those experiments, not a general verdict on all membrane-protein methods or later work.
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The comparison is therefore not simply one study versus another. The Iowa work emphasized direct solid-state NMR measurements in a cholesterol-containing, virus-envelope-mimetic membrane. The Florida work paired lipid-bilayer structural data with simulations and a larger protein construct to propose more detail about proton transfer. Each approach provided a different kind of evidence, and neither alone settled the full molecular mechanism.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why M2 mattered to antiviral research
The M2 channel has been targeted by the adamantane antivirals amantadine and rimantadine. Early structural work examined models in which these drugs block the channel pore or bind at a lipid-facing site. A 2010 study in lipid bilayers reported a high-affinity pore site and a second, lower-affinity surface site at higher drug concentrations. Those are findings about binding under experimental conditions, not a recommendation for treatment.
Resistance mutations have compromised the effectiveness of these drugs against many influenza strains. The 2010 structural studies are therefore best read as basic research into the channel and its possible drug-binding behavior—not as evidence that a new treatment was available or that either adamantane is appropriate for present-day care. The cited structural literature includes a review of M2’s mechanism and drug resistance, as well as the lipid-bilayer binding-site study.
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What the 2010 findings establish
- M2 is an acid-activated influenza A proton channel involved in viral entry.
- Both research groups placed His37 near the center of proton conduction.
- The studies disagreed about the importance of Trp41 and proposed different levels of detail for the transfer pathway.
- The proposed mechanisms explain experimental structural and dynamic evidence; they do not amount to direct observation of each proton handoff.
- The work informs drug-target research, but it does not establish clinical efficacy or current treatment guidance.
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