A coiled-coil (leucine zipper) domain unfolds with a free-energy change (unfolded…

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Macromolecules, membranes and cell architecture · Macromolecules, membranes and cell architecture

Forces, Machines and Signals, Ch Cooperativity: zippers, melting and allosteric binding

Problem

A coiled-coil (leucine zipper) domain unfolds with a free-energy change

\Delta G_0 = 45\,k_BT

(unfolded minus folded, at zero force,

T=298\,\mathrm{K}

) and an end-to-end extension change

\Delta x = 10\,\mathrm{nm}

on unfolding. ((a)) Find the coexistence force

f_{1/2}

at which folded and unfolded states are equally occupied. ((b)) Find the force scale

k_BT/\Delta x

of the transition and its

10

90

per cent width in force.

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