Protein stability temperature adaptation

In this chapter, we will outline how evolutionary protein design methods are now being used to help uncover the molecular basis for temperature adaptation in enzymes. Before doing this, however, we will briefly review how temperature affects protein stability and enzyme activity. Then we will discuss some of the results of comparative studies of enzymes isolated from organisms adapted to different temperatures and the questions that can be addressed by laboratory evolution. 

The high-temperature environments inhabited by thermophiles require adaptations to promote stability of proteins at temperatures that denature proteins from most organisms. A further challenge is that entropic... 

Stability of several enzymes like proteases from thermophilic micro-organisms can be increased in aqueous-organic biphasic systems. Owusu and Cowan [67] observed a strong positive correlation between bacterial growth temperature, the thermostability of free protein extracts, and enzyme stability in aqueous-organic biphasic systems (Table 1). Enzymes, like other cell components (membranes, DNA, (RNA ribosomes), are adapted to withstand the environmental conditions under which the organism demonstrates optimal growth. 

Recently, considerable progress has been made on the calculation of electrostatic and hydrophobic interactions in biochemical systems 189 19 >. We can expect such calculations to become common for protein-solid surface interactions. Thus we can expect approximate values for the adsorption energy in selected systems to appear in the near future. The problem of time-dependent conformational adaptation of the protein to the surface (and vice versa) will be much more difficult. Initially, we will have to resort to crude measures of the structural stability of a protein, such as the temperature at which thermal denaturation occurs, the urea molar concentration for solution denaturation, etc. One or more of the models given in Fig. 13 should apply. 

Active and/or stable enzymes can be generated rapidly. Although natural proteins adapted to different temperatures typically differ from each other at many amino acid positions, only a small number of substitutions are required to confer high degrees of stability and/ or low temperature activity. Some parallel nature, some do not. 

In summary, during protein evolution at different temperatures, selection favors the accumulation of amino acid substitutions whose effects are manifested by adaptive changes in stability and kinetic properties. Of overarching importance is the maintenance of the geometry... 

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