Trade-offs between effectiveness and cost in bifunctional enzyme circuit with concentration robustness

Area of Science:

• Systems Biology
• Biophysics
• Molecular Biology

Background:

• Biological systems face a fundamental trade-off between resource consumption for function and resource conservation.
• Bacteria require rapid and reliable responses to signals using limited cellular resources, but excessive consumption hinders growth.

Purpose of the Study:

• To investigate the relationship between functional effectiveness and resource cost in bacterial systems.
• To analyze the trade-offs in ubiquitous bifunctional enzyme circuits regarding concentration robustness and response speed.

Main Methods:

• Studied bifunctional enzyme circuits, known for robustness to protein concentration fluctuations and rapid signal response.
• Analyzed the trade-off between functional effectiveness and protein cost.
• Investigated the role of free-energy dissipation rate in concentration robustness and response speed.
• Calculated trade-off relationships in specific systems like EnvZ-OmpR and nitrogen assimilation.

Main Results:

• Trade-off relationships exist between functional effectiveness and protein cost in bifunctional enzyme circuits.
• Increased protein expression enhances concentration robustness and response speed but negatively affects bacterial growth.
• Free-energy dissipation is crucial for concentration robustness and response speed, requiring significant free-energy and protein investment.
• Higher protein cost increases output noise while decreasing response time noise.

Conclusions:

• Bifunctional enzyme circuits exhibit inherent trade-offs between performance (robustness, speed) and resource cost (protein, energy).
• Bacteria achieve reliable biological functions through a compromise, balancing performance with resource limitations.
• These findings are general to bifunctional enzyme circuits, not model-specific.