Long-Term Persistence of Bi-functionality Contributes to the Robustness of Microbial Life through Exaptation: e1005836

Modern enzymes are highly optimized biocatalysts that process their substrates with extreme efficiency. Many enzymes catalyze more than one reaction; however, the persistence of such ambiguities, their consequences and evolutionary causes are largely unknown. As a paradigmatic case, we study the his...

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Bibliographic Details
Published in:PLoS genetics 2016-01, Vol.12 (1)
Main Authors: Plach, Maximilian G, Reisinger, Bernd, Sterner, Reinhard, Merkl, Rainer
Format: Article
Language:English
Subjects:
Actinobacteria
Biosynthesis
Cloning
Enzymes
Genes
Genomes
Metabolism
Phylogenetics
Proteobacteria
Trees
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Summary:Modern enzymes are highly optimized biocatalysts that process their substrates with extreme efficiency. Many enzymes catalyze more than one reaction; however, the persistence of such ambiguities, their consequences and evolutionary causes are largely unknown. As a paradigmatic case, we study the history of bi-functionality for a time span of approximately two billion years for the sugar isomerase HisA from histidine biosynthesis. To look back in time, we computationally reconstructed and experimentally characterized three HisA predecessors. We show that these ancient enzymes catalyze not only the HisA reaction but also the isomerization of a similar substrate, which is commonly processed by the isomerase TrpF in tryptophan biosynthesis. Moreover, we found that three modern-day HisA enzymes from Proteobacteria and Thermotogae also possess low TrpF activity. We conclude that this bi-functionality was conserved for at least two billion years, most likely without any evolutionary pressure. Although not actively selected for, this trait can become advantageous in the case of a gene loss. Such exaptation is exemplified by the Actinobacteria that have lost the trpF gene but possess the bi-functional HisA homolog PriA, which adopts the roles of both HisA and TrpF. Our findings demonstrate that bi-functionality can perpetuate in the absence of selection for very long time-spans.
ISSN:1553-7390
1553-7404
DOI:10.1371/journal.pgen.1005836