# Insights into Chemoreceptor MCP2201-Sensing D-Malate

## TL;DR

This paper explores how a bacterial chemoreceptor detects D-malate and how a single mutation changes its response from repelling to attracting.

## Contribution

The study reveals that a single mutation alters the chemotactic response to D-malate and redefines the role of LBD oligomerization in signal transduction.

## Key findings

- D-malate binds to MCP2201 and induces LBD dimerization, triggering a chemorepellent response.
- The T105A mutation switches the LBD dimerization state and changes the chemotactic response to D-malate from negative to positive.
- LBD oligomerization is a consequence of signal transduction rather than a trigger.

## Abstract

Bacterial chemoreceptors sense extracellular stimuli and drive bacteria toward a beneficial environment or away from harm. Their ligand-binding domains (LBDs) are highly diverse in terms of sequence and structure, and their ligands cover various chemical molecules that could serve as nitrogen, carbon, and energy sources. The mechanism of how this diverse range of LBDs senses different ligands is essential to signal transduction. Previously, we reported that the chemoreceptor MCP2201 from Comamonas testosteroni CNB-1 sensed citrate and L-malate, altered the ligand-free monomer–dimer equilibrium of LBD to citrate-bound monomer (with limited monomer) and L-malate-bound dimer, and triggered positive and negative chemotactic responses. Here, we present our findings, showing that D-malate binds to MCP2201, induces LBD dimerization, and triggers the chemorepellent response exactly as L-malate did. A single site mutation, T105A, can alter the D-malate-bound LBD dimer into a monomer–dimer equilibrium and switch the negative chemotactic response to D-malate to a positive one. Differences in attractant-bound LBD oligomerization, such as citrate-bound wildtype LBD monomer and D-malate-bound T105A dimer, indicated that LBD oligomerization is a consequence of signal transduction instead of a trigger. Our study expands our knowledge of chemoreceptor-sensing ligands and provides insight into the evolution of bacterial chemoreceptors.