Enzymes adaptive mutations

The number of thermally adaptive mutations resulting from directed evolution studies is too small at present to support a detailed statistical analysis. Here we summarize some properties of the mutations discovered in the studies reviewed above, and compare them to the amino-acid differences seen among naturally occurring enzymes that have adapted to different temperatures. Lists of the amino-acid substitutions discovered... 

Recent laboratory experiments followed the notion of a neutral drift by placing an enzyme under mutation and selection to maintain its native function. The data provide empirical evidence in support of the hypothesis that neutrality enables the formation of latent changes, or latent adaptation . It was found ° that latent evolutionary potentials are indeed very frequent within a neutral set of related enzyme mutants, and that these potentials are most often seen as changes in specificity for one or more promiscuous substrates. 

Benning, M.M., Taylor, K.L., Liu, R.-Q., Yang, G, Xiang, H., Wesenbeig, G, Dunaway-Mariano, D. Holden, H.M. (1996) Biochemistry, 35, 8103-8109, Structure of 4-chlorobenzoyl coenzyme A dehalogenase determined to 1.8 A resolution an enzyme eatalyst generated via adaptive mutation. 

Resistance, Immunity, Adaptation, Mutations, and Chemotherapy, and Enzyme Problems (Sevag). VI 33... 

Enzyme Problems in Relation to Chemotherapy, Adaptation," Mutations, Resistance, and Immunity (Sevag). VI... 

The plot of the stabilities and activities of clones from the first generation S41 random mutant library shows once again that most mutations are detrimental to stability and activity (Fig. 14). However, compared to the esterase library (Fig. 7), there are more mutants with improvements in both properties, suggesting that the two enzymes have different adaptive potentials. This may be due to the relatively poor stability of S41, or it may reflect constraints intrinsic to the three-dimensional structures of the two proteins. Evidence for the former can be found by comparing the results for the first generations of the psychrophilic sub-tilisin S41 and the mesophilic subtilisin E. Screening 864 mutants of S41 yielded nine thermostabilized variants (a hit rate of approximately 1%) (Miyazaki and Arnold, 1999) in contrast, screening 5000 subtilisin E mutants identified five thermostable variants (a hit rate of only 0.1%) (Zhao and Arnold, 1999). 

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