# A new regulator of the Staphylococcus aureus peptidoglycan hydrolase Sle1

## TL;DR

Researchers discovered a new protein, CxaR, that controls the activity of Sle1 in Staphylococcus aureus, a key enzyme involved in cell division.

## Contribution

CxaR is identified as a novel negative regulator of Sle1, controlling its degradation via the ClpXP protease.

## Key findings

- CxaR absence causes a ten-fold increase in Sle1 levels, leading to premature cell lysis.
- CxaR localizes to the division septum late in the cell cycle, requiring FtsK and ClpX.
- CxaR is proposed to direct Sle1 to ClpXP for degradation.

## Abstract

Regulation of peptidoglycan hydrolases is crucial for bacterial cell integrity, growth and division. In the bacterial pathogen Staphylococcus aureus, the amidase Sle1 is a key autolysin required for septum splitting and daughter cell separation. Through genetic suppressor screening, we have identified CxaR, a previously uncharacterized protein, as a novel negative regulator of Sle1. In the absence of CxaR, cellular levels of Sle1 increase nearly ten-fold, resulting in premature splitting of the division septum and increased cell lysis during exponential growth. CxaR localizes to the division septum, late in septum synthesis, and this localization requires both the divisome protein FtsK and the ClpX component of the ClpXP proteolytic machinery. We propose that CxaR promotes ClpXP-mediated degradation of Sle1 towards the end of the cell cycle.

The final step in cell division of the major pathogen Staphylococcus aureus is the separation of the two newly formed daughter cells, a process that relies on the autolysin Sle1 to cleave the cell-wall layer between them. Because this layer is essential for maintaining cell integrity, Sle1’s activity must be tightly controlled. If Sle1 acts at the wrong time, it can breach the dividing wall too early, weakening the bacteria and potentially increasing their vulnerability to host defenses and lysis. Understanding how this enzyme is regulated is likely to enable new strategies for harnessing Sle1 as a lysis agent to more effectively combat S. aureus infections in the future. In this study, we identified a previously unknown regulator of Sle1, CxaR. The absence of CxaR leads to a nearly ten-fold increase in Sle1 levels, causing premature septum splitting and making cells more prone to lysis during growth. We further found that CxaR accumulates at the division site late in the cell cycle, a process that requires the divisome protein FtsK and the protease adaptor ClpX. Together, these findings support a model in which CxaR directs Sle1 to the ClpXP protease for controlled degradation.