Thermophiles evolution

Baross JA. 1998. Do the geological and geochemical records of the early Earth support the prediction from global phylogenetic models of a thermophilic ancestor In Wiegel J, Adams M, editors. Thermophiles the keys to molecular evolution and the origin of life London Taylor Francis, pp. 13-18. 

Proteins from extremophilic organisms, particularly thermophiles, have been the subject of intensive research in recent years. This work has been the subject of numerous reviews (Jaenicke and Bohm, 1998 Russel and Taylor, 1995 Vogt and Argos, 1997 Gerday et al., 1997 Somero, 1995), and we will make no attempt at an in-depth summary. We will confine ourselves to briefly stating the major trends identified thus far. Explaining these trends becomes complicated because the many weak interactions that determine enzyme stability and activity have complex temperature dependencies (see Section II). And evolution injects considerable confusion beyond the laws of physical chemistry. 

Although assays based on the retention of room temperature activity after heat treatment are convenient, the constraints imposed during the laboratory evolution can be quite different Ifom anything an enzyme in a natural thermophilic organism might have encountered. Retaining activity at moderate temperatures is probably not relevant for enzymes... 

Fig. 10. Sequence alignment of subtilisins S41, SSII, S39, BPN, E, Carlsberg, and thermitase. Thermitase is an homologous subtilisin-like protease from the thermophilic bacterium Thermoactinomyces vulgaris. Residues conserved in four or more of the sequences are shaded. The positions of mutations discovered during the directed evolution of the various subtilisins are indicated above the alignment. E-subtilisin E, F-subtilisin S41, S-subtilisin SSII, B-subtilisin BPN. Active site residues are indicated (A).

Directed evolution as a tool to probe the basis of protein structure, stability, and function is in its infancy, and many fruitful avenues of research remain to be explored. Studies so far have focused on proteins that unfold irreversibly, making detailed thermodynamic analysis impossible. The application of these methods to reversibly folding proteins could provide a wealth of information on the thermodynamic basis of high temperature stability. A small number of studies on natural thermophilic proteins have identified various thermodynamic strategies for stabilization. Laboratory evolution makes it possible to ask, for example, whether proteins have adopted these different strategies by chance, or whether certain protein architectures favor specific thermodynamic mechanisms. It will also be possible to determine how other selective pressures, such as the requirement for efficient low temperature activity, influence stabilization mechanisms. The combination of directed evolu-... 

The most thermophilic variant of j/NB esterase, 8G8, has only thirteen mutations compared to the wild-type esterase, making it 97% identical to the wild-type esterase sequence, with a root-mean-square deviation of only 0.44 A between the two C backbone structures. As with the 5-6C8 organophile structure, the catalytic triads of 8G8 and wild-type / NB esterase are superimposable. This high sequence and structural identity, in conjunction with the availability of crystal structures for both the wild type and thermophile, affords an interesting opportunity to study the structural basis for thermostability. Thermophile 8G8 is the product of eight generations of directed evolution, screening for retention of activity... 

Russell, M. J., Daia, D. E., and Hall, A. J., 1998, The emergence of life from EeS bubbles at alkaline hot springs in an acid ocean. Thermophiles The keys to molecular evolution and the origin of life M. W. W. Adams, L. G. Ljungdahl, and J. Wiegel. Washington, D.C.,Taylor... 

A deep understanding of the physical mechanisms and the evolution of thermophilic adaptation is cmcial for the engineering and design of biologic catalysts with desired stability (20). This... 

Lehmann M, Wyss M. Engineering proteins for thermostability the use of sequence alignments versus rational design and directed evolution. Curr. Opin. Biotechnol. 2001 12 371-375. Berezovsky IN, Shakhnovich El. Physics and evolution of thermophilic adaptation. Proc. Natl. Acad. Sci. U.S.A. 2005 102 12742-12747. 

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