We use a combination of single-molecule approaches to decipher this protein’s mechanism. Fluorescence microscopy is used to visualize quantum dot-labeled TelK interactions with DNA. Interestingly, we observe that TelK undergoes 1D diffusion on nonspecific DNA as a monomer, as expected, but becomes immobile upon dimerization and aggregation despite the absence of a DNA target-site. Complementary high-resolution optical trap studies unexpectedly show that TelK condenses nonspecific DNA, forming a tightly bound nucleo-protein complex upon dimerization. We hypothesize that dimer or oligomer-active proteins may use this indiscriminate tight-binding mechanism as a form of potential energy storage for eventual energy-expensive DNA rearrangements, or as a mechanism for increased affinity for the DNA target sequence. These novel experimentally detected interactions between TelK and nonspecific DNA may be generalizable to many other protein families.
Our results indicate a search mechanism where monomers diffuse along DNA and dimerize at the target site. Theoretical calculations validate experimental data, providing a comprehensive and novel target-search model for proteins-DNA systems that are more than just monomer-active.