Cells must detect changing levels of oxygen, carbon monoxide, and nitric oxide, but the molecular steps that connect gas sensing to a biological response remain complex.
A new review brings together evidence on heme-based gas sensors and on labile heme, the small and dynamic fraction of heme that can regulate proteins directly.
Across diverse proteins, the same principle emerges: minute changes around heme's iron atom are amplified into larger protein movements that control cellular activity.
The review identifies unresolved steps in this process and highlights time-resolved structural studies and cellular imaging as routes toward synthetic biosensors and therapies targeting heme-mediated pathways.
Heme is an iron-containing molecular group best known for helping hemoglobin carry oxygen, but its biological roles extend far beyond transport. In heme-based sensor proteins, oxygen, carbon monoxide, or nitric oxide can bind at the iron center and change the activity of another part of the protein. These sensors use different protein structures and regulate functions ranging from microbial metabolism and movement to circadian regulation and mammalian signaling. A central challenge is to understand the shared molecular logic that converts a tiny chemical change at heme into a much larger biological response.
The review organized heme-based sensors according to the gas they primarily detect and compared structural, spectroscopic, biochemical, and functional evidence for how their signals are transmitted. It also examined representative systems in which heme itself acts as a reversible signaling molecule; no new experimental data were generated or analyzed for the article.
The review identifies a common operating principle across otherwise diverse sensors: gas binding or a change in the iron's oxidation state alters the electronic and coordination properties of the heme center and the amino acid groups attached directly to it. This local event can pull on nearby amino acids and amplify a movement smaller than one-tenth of a nanometer into protein rearrangements on the nanometer scale. The resulting allosteric effect--where a change at one site controls a distant part of the protein--can regulate gene expression, enzyme activity, metabolism, and cell movement. The review also highlights labile heme, a small and tightly regulated cellular pool that binds reversibly to targets such as transcription factors and ion channels instead of remaining permanently embedded in a sensor protein.
By showing that many heme sensors share the same underlying design principle, the review offers a framework for understanding how cells translate chemical information into precise responses. It emphasizes that these systems are often not simple on-or-off switches, but can provide graded and finely tuned sensitivity as environmental conditions change. Important gaps remain because X-ray crystallography and cryo-electron microscopy mainly provide static views, while transient intermediate structures and real-time communication between sensor and effector regions remain poorly understood. Combining time-resolved structural biology with cellular imaging could clarify these processes and may support the rational design of synthetic biosensors and therapeutic strategies aimed at heme-mediated regulation.
Authors: Shigetoshi Aono
Journal Name: Bulletin of the Chemical Society of Japan
Article Type : Review Article
Journal Title: "The heme prosthetic group: a versatile tool for environmental sensing"
DOI: 10.1093/bulcsj/uoag056
Bulletin of the Chemical Society of Japan
Literature review
The heme prosthetic group: a versatile tool for environmental sensing
29-Apr-2026