Fundamental constraints on the abundances of chemotaxis proteins

TL;DR

This paper investigates the biological constraints on chemotaxis protein abundances in bacteria, revealing how signaling speed, self-assembly, and robustness shape protein expression levels in E. coli.

Contribution

It identifies specific constraints on chemotaxis protein levels and demonstrates how these influence pathway gain and robustness, advancing understanding of bacterial signal transduction.

Findings

High protein abundances are required for fast chemotaxis signaling.

Self-assembly constraints influence chemotaxis protein expression.

Chemotaxis pathway gain increases with protein abundance.

Abstract

Flagellated bacteria, such as Escherichia coli, perform directed motion in gradients of concentration of attractants and repellents in a process called chemotaxis. The E. coli chemotaxis signaling pathway is a model for signal transduction, but it has unique features. We demonstrate that the need for fast signaling necessitates high abundances of the proteins involved in this pathway. We show that further constraints on the abundances of chemotaxis proteins arise from the requirements of self-assembly, both of flagellar motors and of chemoreceptor arrays. All these constraints are specific to chemotaxis, and published data confirm that chemotaxis proteins tend to be more highly expressed than their homologs in other pathways. Employing a chemotaxis pathway model, we show that the gain of the pathway at the level of the response regulator CheY increases with overall chemotaxis protein abundances. This may explain why, at least in one E. coli strain, the abundance of all chemotaxis proteins is higher in media with lower nutrient content. We also demonstrate that the E. coli chemotaxis pathway is particularly robust to abundance variations of the motor protein FliM.