Interactions between PHD3-Bromo of MLL1 and H3K4me3 Revealed by Single-Molecule Magnetic Tweezers in a Parallel DNA Circuit

Single-molecule force spectroscopy is a powerful tool to directly measure protein-protein interactions (PPI). The high specificity and precision of PPI measurements made it possible to reveal detailed mechanisms of intermolecular interactions. However, protein aggregation due to specific or non-specific interactions are among the most challenging problems in PPI examination. Here, we propose a strategy of a parallel DNA circuit to probe PPI using single-molecule magnetic tweezers. In contrast to PPI examination using atomic force microscopy, microspheres as probes used in magnetic tweezers avoided the single-probe issue of a cantilever. Negatively charged DNA as a linker circumvented the sever aggregation in PPI construct with a protein linker. The unnatural amino acid encoded in proteins of interest expanded the choices of biorthogonal conjugation. We demonstrated how to apply our strategy to probe the PPI between the PHD3-Bromo and the histone H3 methylated at K4, a critical epigenetic event in leukemia...