Facilitated Unbinding via Multivalency-Enabled Ternary Complexes: New Paradigm for Protein-DNA Interactions

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Protein-DNA interactions are fundamental to cellular functions, with significant research on protein binding regulation.
• Protein unbinding from DNA is traditionally viewed as a concentration-independent unimolecular reaction.
• Emerging single-molecule studies challenge this view, suggesting concentration can influence protein unbinding.

Purpose of the Study:

• To review recent single-molecule experiments investigating concentration-facilitated protein unbinding from DNA.
• To explore this phenomenon across diverse DNA-binding proteins, including transcription regulators, polymerases, and nucleoid-associated proteins.
• To elucidate the underlying mechanistic principles and potential generality of this regulatory paradigm.

Main Methods:

• In vitro single-molecule techniques: magnetic tweezers, fluorescence resonance energy transfer (FRET), DNA curtain assays.
• In vivo single-molecule tracking and stroboscopic imaging in living bacterial cells.
• Analysis of protein exchange, dwell times, and processivity under varying protein concentrations.

Main Results:

• Demonstrated concentration-enhanced unbinding for nucleoid-associated proteins (NAPs), transcription regulators (CueR, ZntR), Replication protein A (RPA), and DNA polymerases.
• Observed faster exchange rates and shorter dwell times with increasing free protein concentrations.
• Confirmed concentration-enhanced unbinding in vivo for CueR and ZntR in bacterial cells.

Conclusions:

• Protein concentration can actively facilitate protein unbinding from DNA, representing a novel regulatory mechanism.
• The mechanism involves multivalent protein-DNA contacts, enabling ternary complex formation and subsequent facilitated dissociation.
• This multivalency-enabled facilitated unbinding offers a potentially general paradigm for regulating diverse protein-DNA interactions.