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This study shifts the focus from concentration-based measurements to volume-based control in quantifying weak molecular interactions, addressing a long-standing bottleneck in biochemistry. By utilizing nanoscale spatial confinement, the authors demonstrated that manipulating the accessible volume can significantly enhance the detection of weak affinities, allowing for the quantification of interactions previously deemed too weak to measure. The approach not only achieves a high signal-to-noise ratio in detecting weak interactions but also facilitates the rational screening of compounds that modulate protein-protein interactions by altering local encounter dynamics.
Shifting the paradigm from concentration to volume control reveals a new way to quantify weak molecular interactions, unlocking previously inaccessible affinity ranges.
A vast class of weak, millimolar-affinity molecular interactions governs cellular function, yet their quantitative characterization has remained largely beyond conventional methods. For over a century, biochemistry has worked within a concentration-based framework where molarity scales with molecular number per volume (N/V), and experiments have usually, often implicitly, changed concentration by moving N while holding V fixed. The weak-interaction measurement bottleneck arises from this paradigm: reading weak binding through bulk concentration requires concentrations beyond practical limits, a framework constraint rather than one of instrumental sensitivity. Here we show that shifting experimental control from N to accessible volume V overcomes this bottleneck and opens previously intractable affinity ranges through nanoscale spatial confinement. Controlling V means controlling what biochemists have called"local concentration"and"proximity effects,"recasting these long-ambiguous notions as quantitative variables grounded in first principles. Implemented in DNA nanocavities, the approach showed that geometric arrangement alone can override solution-phase binding hierarchies. The same spatial control quantified a protein-peptide interaction of order 10 mM from femtomoles per well, totalling under a picomole per titration. Even so, a standard plate reader gave a signal-to-noise ratio near 10^3, leaving headroom for still weaker interactions. The affinity-and-geometry readout also enabled rational screening for protein-protein-interaction modulators, identifying compounds that enhance weak associations by reweighting local encounters rather than binding tightly on their own or forming a stable ternary complex. Together, this volume-based paradigm and its implementation provide a general strategy for probing and modulating previously inaccessible biochemical phenomena.