Protein sensor lets MRI detect molecular activity ^{CEFR B2}

Researchers report in Science Advances a modular, genetically encoded, protein-based sensor that can make molecular activity visible to magnetic resonance imaging (MRI). MRI works by aligning hydrogen atoms and using radio waves to create an image, but it typically shows tissue structure rather than molecular changes inside cells. The new sensor changes that by altering how water moves across cell membranes.

The design centers on aquaporin, a protein that forms water channels. Arnab Mukherjee, an associate professor of chemical engineering at UCSB, explains that controlling water movement can make the MRI signal specific to particular cells or processes: "Our water molecules are tiny, tiny magnets." Mukherjee began work on the problem as a postdoctoral researcher at Caltech and continued after he arrived at UCSB in 2017. The team combined aquaporin with other proteins to build interchangeable genetic circuits, and a PhD student helped tune the system. Asish Ninan Chacko says, "This protein can be regulated using a lot of chemical signals," and parts can be swapped to detect different targets.

The system, named MAPPER (modular aquaporin-based protease-activatable probes for enhanced reporting), can detect nearly ten systems according to the paper, while prior literature described only four or five genetic sensors. The researchers say the building-block design should let other groups develop new sensors faster. They expect MAPPER to enable continuous imaging in animal studies, reducing the need to sacrifice animals for internal measurements, and Mukherjee hopes to train students and make the tools available to neuroscientists and developmental biologists.