Divergence protein evolution

Comparison of the amino acid sequences of hemoglobin and myoglobin chains from different species of animals shows that the chains from related species are similar. The number of differences increases with phylogenetically more separated species. On the assumption that proteins evolve at a constant rate, the number of differences between two homologous proteins will be proportional to the time of divergence in evolution of the species. 

The primary focus of this chapter is the role of promiscuity in the evolution of new enzyme functions. New enzymes have constantly emerged throughout the natural history of this planet. Over the past decades, enzymes that degrade synthetic chemicals were introduced to the biosystem, and enzymes associated with drug resistance, provide vivid examples of how rapid the evolution of new enzymatic functions can be. The first direct connection between protein evolution and promiscuity was made in 1976 by Jensen. In his landmark review, Jensen formalized the hypothesis that the starting points for evolution were provided by broad specificity, or promiscuity, of the ancestral enzymes. Jensen proposed that unlike modern enzymes that tend to specialize in one substrate and reaction, the primordial, ancient enzymes possessed very broad specificities, and thus few enzymes could perform many functions. Divergence of specialized enzymes, through duplication, mutation, and selection, led to the current diversity of enzymes, and to increased metabolic efficiency. 

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Wise EL, Rayment I. 2004. Understanding the importance of protein structure to nature s routes for divergent evolution in TIM barrel enzymes. Acc Chem Res 37 149-158. 

The AdoMet binding motif is similar to the Rossmann fold, which is well known from the nucleotide binding proteins [22]. It has been shown that the known crystal structures of methyltransferases are strikingly similar in the AdoMet-binding regions [23], which indicates that all AdoMet-utilizing enzymes may share a common divergent evolution. 

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