Biology’s Unique Phase Transition Drives Cell Function

Abstract

Systematic designs, physical characterizations and data analyses of elastic-contractile model proteins have given rise to a series of physical concepts associated with phase transitions of hydrophobic association and with the nature of elasticity that provide new insight into the function of a number of protein machines, namely, 1) Complex III of the electron transport chain wherein electron transfer pumps protons across the inner mitochondrial membrane, 2) the F₁-motor of ATP synthase that uses return of protons to produce the great majority of ATP in living organisms, 3) the myosin II motor of muscle contraction that uses ATP hydrolysis to produce movement, 4) the kinesin bipedal motor that walks along microtubules to transport cargo within the cell, and 5) the calcium-gated potassium channel. The physical processes utilize an understanding of the change in Gibbs free energy due to hydrophobic association, Δ G _HA , the water-mediated repulsion between hydrophobic domains and charged groups, Δ G _ap , and stretching of interconnecting chain segments that attends hydrophobic association