ELASTICITY OF GLOBULAR-PROTEINS - THE RELATION BETWEEN MECHANICS, THERMODYNAMICS AND MOBILITY

An analysis of elasticity of lysozyme and myoglobin crystals in terms of thermodynamics has revealed a direct relation between entropy and e nthalpy of deformation and Delta S and Delta H* terms in the standard free energy change in proteins, Delta G(0), (K.P.Murphy, P.L. Privalo v, S.J. Gill(1990) Science 247, 559-561), so that at any temperature ( between the glass-transition and denaturation temperatures) free energ y of deformation is proportional to the hydration independent part of Delta G(0). Both energies are characterized with large enthalpy-entrop y compensation and tend to zero at the same temperature, T-m = (Delta H/Delta S*) = 353 +/- 20 K. Large positive entropy contribution to de formation energy causes large linear decrease in protein elasticity, a nd increase in thermal mobility of protein atoms with temperature. Bei ng plotted in inverse coordinates, temperature dependence of the mean- square amplitudes, obtained in neutron and mossbauer experiments as we ll as in molecular dynamic simulations, gives the same 353 +/- 10 K fo r the temperature, where the amplitudes tend to infinity. Mechanism ex plaining large possitive entropy contribution in deformation energy of native protein molecules presumably involves emergence of more room f or motion of protein side-chain groups squized between alpha-helices a nd other rigid sceleton elements, when precise packing of atoms in nat ive protein molecule is distorted as a result of deformation.