Evolution of enzyme levels in metabolic pathways: A theoretical approach. Part 2
Metabolism is essential for cell function and adaptation. Because of their central role in metabolism, kinetic parameters and enzyme concentrations are under constant selective pressure to adapt the fluxes of the metabolic networks to the needs of the organism. In the line of various studies dealing with enzyme evolution, we recently developed a model of evolution of enzyme concentrations under selection for increased flux, considered as a proxy of fitness (Coton et al. 2021). Taking into account two realistic cellular constraints, competition for resources and co-regulations, we determined the evolutionary equilibria and the ranges of neutral variations of enzyme concentrations. In this article, we give more generality to this model, by considering that the enzymes of a pathway can belong to different groups of co-regulation. We determined the equilibria and showed that the constraints modify the adaptive landscape by limiting the number of independent dimensions. We also showed that any trade-off between enzyme concentration is sufficient to limit the flux and to relax selection for increasing other enzyme concentrations. Even though the model is based on simplifying assumptions, the complexity of the relationship between enzyme concentrations prevents the analysis of selective neutrality.