Conformation-gated dual enzyme activity in a hemoglobin-based gadolinium single-atom catalyst for adaptive biosensing.

Single-atom catalysts (SACs) are known for their exceptional catalytic efficiency but suffer from structural rigidity, limiting their adaptability in biological environments. Here, we present a hemoglobin-based gadolinium single-atom catalyst (Hb-Gd SAC), in which Gd atoms are site-specifically anchored adjacent to the native heme-Fe center via biomimetic coordination. Leveraging the intrinsic flexibility of the protein scaffold, the system exhibits pH- and conformation-gated switching between two distinct enzymatic modes: peroxidase-like (POD-like) activity under acidic conditions and laccase-like activity at neutral pH. These catalytic modes are mechanistically decoupled-global protein conformation governs POD activity, while localized Gd coordination drives laccase-like function. Allosteric regulation by tartaric acid further fine-tunes this behavior, significantly enhancing performance beyond that of natural horseradish peroxidase. This dual-mode catalysis supports programmable biosensing: POD mode enables detection of thiols and acetylcholinesterase activity, while the laccase mode selectively targets dopamine. Such multimodal detection is particularly relevant for neurodegenerative disease diagnostics, exemplified by Parkinson's disease, where simultaneous monitoring of oxidative stress, cholinergic dysfunction, and dopaminergic signaling is essential. Our findings introduce a reconfigurable SAC platform that couples atomic precision with biomolecular dynamics, advancing the frontier of intelligent catalysis and adaptive biosensing technologies.