Detection of Structural Changes in G-Quadruplex-Forming DNA Oligonucleotides via DNA Methylation Based on Luminol Chemiluminescence Catalyzed by Myoglobin

A novel, label-free chemiluminescence sensing platform for CpG methylation was developed, leveraging the G-quadruplex (G4) structural sensitivity of G4-protein interactions to eliminate bisulfite conversion. This sensing system is based on the enhancement of luminol chemiluminescence generated from myoglobin upon binding to the G4-forming DNA. At the core of this biosensor is the G4-structure-dependent modulation of the peroxidase-like activity generating luminol chemiluminescence of myoglobin. The structural change by CpG methylation within the G4-forming sequence of the B cell lymphoma 2 (BCL2) gene promoter altered its binding to myoglobin, transducing the methylation state into a measurable signal catalyzed by myoglobin. This principle was validated in a practical assay using immobilized probes to capture the target DNA for methylation analysis. This system demonstrated the capability to distinguish methylation differences of 50% when the target DNA concentration was over 25 nM. Versatility was further confirmed using the sequence from the dopamine receptor D2 (DRD2) gene promoter, where the methylation similarly induced distinct topological and functional changes. This is the first study to directly link the epigenetic state of a G4-forming DNA sequence to a protein-mediated enzymatic output, offering a framework for simple, rapid, and highly adaptable biosensors for research and clinical applications.