Molecular and thermodynamic mechanisms for protein adaptation.

Using thermal adaptation of enzymes as an example, we have proposed a molecular and thermodynamic model for protein adaptation. Key concepts: (1) The working mechanism of enzymatic reactions is not altered in protein adaptation, but the activity of the adapted enzyme is expressed under altered conditions. (2) The alteration of protein conformational stability induced by gene mutation is the fundamental cause of protein adaptation. (3) The population change in active conformations of enzymes induced by protein conformational stability in different temperature ranges is the major cause of protein adaptation. (4) The features of enzyme adaptation must be analyzed or judged by two different aspects: local population change in active conformations near a critical level of an environmental factor; and the position of the whole active conformational curve in the gradient of an environmental factor. (5) Protein adaptation represents a specific mechanism for protein regulation. Several other aspects of protein adaptation are also discussed and reviewed, and specific examples are given of enzymes showing particular types of adaptation.