In vitro evolution of thermodynamically stable turns


To determine the role of primary structure in specifying turns, random sequences (guests) were substituted for the native turn sequences in a series of proteins (hosts) of differing thermo-dynamic stabilities.The fraction of inserts that result in active proteins is measured as a function of the stability of the host and temperature. With a highly stable host more than half of the inserts give functional proteins. However, a smaller fraction of sequences supports folding as the stability of the host decreases, and the temperature increases. The sequences of many of the selected inserts resemble the wild-type turn, and those that diverge match other established turn preferences. Thermodynamic measurements show that turn sequences selected under stringent conditions result in the most stable proteins. Thus, β-turns appear to be under evolutionary pressure favouring thermodynamically stable structures.

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Zhou, H., Hoess, R. & DeGrado, W. In vitro evolution of thermodynamically stable turns. Nat Struct Mol Biol 3, 446–451 (1996).

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