Abstract
Protein promiscuity is of considerable interest due its role in adaptive metabolic plasticity, its fundamental connection with molecular evolution and also because of its biotechnological applications. Current views on the relation between primary and promiscuous protein activities stem largely from laboratory evolution experiments aimed at increasing promiscuous activity levels. Here, on the other hand, we attempt to assess the main features of the simultaneous modulation of the primary and promiscuous functions during the course of natural evolution. The computational/experimental approach we propose for this task involves the following steps: a function-targeted, statistical coupling analysis of evolutionary data is used to determine a set of positions likely linked to the recruitment of a promiscuous activity for a new function; a combinatorial library of mutations on this set of positions is prepared and screened for both, the primary and the promiscuous activities; a partial-least-squares reconstruction of the full combinatorial space is carried out; finally, an approximation to the Pareto set of variants with optimal primary/promiscuous activities is derived. Application of the approach to the emergence of folding catalysis in thioredoxin scaffolds reveals an unanticipated scenario: diverse patterns of primary/promiscuous activity modulation are possible, including a moderate (but likely significant in a biological context) simultaneous enhancement of both activities. We show that this scenario can be most simply explained on the basis of the conformational diversity hypothesis, although alternative interpretations cannot be ruled out. Overall, the results reported may help clarify the mechanisms of the evolution of new functions. From a different viewpoint, the partial-least-squares-reconstruction/Pareto-set-prediction approach we have introduced provides the computational basis for an efficient directed-evolution protocol aimed at the simultaneous enhancement of several protein features and should therefore open new possibilities in the engineering of multi-functional enzymes.
Highlights
Proteins are capable to perform molecular tasks with impressive efficiency and, often, with exquisite specificity
Concluding remarks Current views on the relation between primary and promiscuous protein activities are derived to a significant extent from laboratory evolution experiments aimed at enhancing promiscuous functions
We have introduced an approach to determine how the interplay between the primary and promiscuous activities of a protein is modulated in the mutational space evolutionary linked to the emergence of a new function
Summary
Proteins are capable to perform molecular tasks with impressive efficiency and, often, with exquisite specificity. As a solution to this conundrum, a ‘‘weak trade-off’’ scenario has been proposed [5]: enhancement of the promiscuous activity is assumed to be accompanied with only a moderate decrease in primary function and, a generalist protein (significant levels of both activities) can be formed prior to gene duplication without seriously impairing organism fitness. This weak trade-off explanation is certainly supported by a number of laboratory evolution experiments [5]. The possibility that natural evolution may avoid or bypass primary/promiscuous activity tradeoffs (i.e., a ‘‘no trade-off’’ scenario as opposed to a ‘‘weak tradeoff’’ scenario) should be seriously taken into account, since bifunctional enzymes with the capability to catalyze efficiently
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