Mutational Pathways and Trade-Offs Between HisA and TrpF Functions: Implications for Evolution via Gene Duplication...

Area of Science:

• Enzymology
• Evolutionary Biology
• Biochemistry

Background:

• Enzyme evolution can lead to functional trade-offs, where acquiring a new activity may diminish the original function.
• The strength of this trade-off influences evolutionary pathways: strong trade-offs favor gene duplication and specialization, while weak trade-offs may permit the evolution of bi-functional enzymes.
• Previous work suggested a strong trade-off between HisA and TrpF functions, leading to specialization.

Purpose of the Study:

• To investigate the mutational landscape of Salmonella enterica HisA enzyme conferring TrpF activity.
• To analyze the functional trade-offs between the original HisA activity and the newly acquired TrpF activity.
• To test the hypothesis that a strong trade-off drives evolution towards specialization.

Main Methods:

• Identification of single mutations in HisA that confer TrpF activity.
• Assessment of residual HisA activity in TrpF-active mutants.
• Further evolution of TrpF-active mutants to examine the impact on original HisA activity.

Main Results:

• Multiple mutational pathways were identified for acquiring TrpF activity from HisA.
• Only a small fraction of mutations conferring TrpF activity retained HisA activity.
• Further evolution for enhanced TrpF activity invariably resulted in the complete loss of HisA activity.
• The study identified numerous distinct mutational pathways, each associated with a unique trade-off profile.

Conclusions:

• The evolution of new enzyme functions from existing ones is strongly influenced by the nature of the functional trade-off.
• A strong trade-off between native and novel functions, as observed here, promotes specialization via duplication-divergence.
• Factors like mutation supply and the shape of the trade-off curve dictate whether enzymes evolve into specialists or generalists.