While the entropic contribution of a single side chain may appear small, accumulating numerous conformational redistributions across the protein can lead to a significant entropic impact and provide an allosteric source of free energy. Structural descriptions of allostery are frequently based on averaged single conformer structures and described in a "domino effect" of conformational changes through a well-defined pathway . But over 40 years ago, Cooper & Dryden postulated that protein thermal fluctuations, without change in mean atomic positions, were sufficient to provide "dynamic allostery" between sites . This model can be reconciled with the domino effect by examining allostery through a thermodynamic lens where any change in the conformational ensemble, whether large or small, can impact free energy and protein function through both entropy and enthalpy .