Macromolecular crowding explains overflow metabolism in cells.

Area of Science:

• Cellular metabolism
• Microbial physiology
• Systems biology

Background:

• Overflow metabolism is a cellular phenotype combining oxidative phosphorylation (OxPhos) and fermentative glycolysis under aerobic conditions.
• Previous theories for Escherichia coli proposed protein allocation constraints and differential energy costs of OxPhos versus fermentation as drivers.
• The role of cellular physical constraints, such as macromolecular density, in overflow metabolism remained underexplored.

Purpose of the Study:

• To re-evaluate the theory of overflow metabolism by incorporating the concept of molecular crowding.
• To investigate the necessity of a maximum or optimal macromolecular density for overflow metabolism.
• To elucidate the contribution of molecular crowding to the metabolic switch from OxPhos to overflow metabolism in Escherichia coli.

Main Methods:

• Re-evaluation of existing overflow metabolism theory using a proteomic fractions formulation.
• Integration of molecular crowding principles into metabolic modeling.
• Analysis of how macromolecular density affects the balance between OxPhos and fermentation.

Main Results:

• The study demonstrates that molecular crowding is a critical factor in overflow metabolism.
• A maximum or optimal macromolecular density is identified as an essential requirement for this metabolic phenotype.
• Molecular crowding effectively explains the metabolic switch from predominantly OxPhos to overflow metabolism.

Conclusions:

• Molecular crowding, in conjunction with protein allocation and energy costs, is fundamental to understanding overflow metabolism.
• The physical constraint of macromolecular density plays a key role in regulating cellular metabolic strategies.
• This revised theory provides a more comprehensive explanation for overflow metabolism in Escherichia coli.