Endopeptidase Regulation as a Novel Function of the Zur-Dependent Zinc Starvation Response

Abstract

Bacteria encode a variety of adaptations that enable them to survive during zinc starvation, a condition which is encountered both in natural environments and inside the human host. In Vibrio cholerae, the causative agent of the diarrheal disease cholera, we have identified a novel member of this zinc starvation response, a cell wall hydrolase that retains function and is conditionally essential for cell growth in low-zinc environments. Other Gram-negative bacteria contain homologs that appear to be under similar regulatory control. These findings are significant because they represent, to our knowledge, the first evidence that zinc homeostasis influences cell wall turnover. Anti-infective therapies commonly target the bacterial cell wall; therefore, an improved understanding of how the cell wall adapts to host-induced zinc starvation could lead to new antibiotic development. Such therapeutic interventions are required to combat the rising threat of drug-resistant infections.

pH-dependent activation of cytokinesis modulates Escherichia coli cell size

“…Although the underlying molecular mechanisms remain unclear, media osmolarity affects the growth of cells harboring conditional mutants of division genes, dictates essentiality of FtsEX for division, and modulates cell size in E. coli [47,87,88]. Extracellular metal availability also alters the activity of several nonessential cell wall enzymes [89][90][91]. Improved understanding of how extracellular processes cope with dynamic environments promises to shed light on how single celled organisms survive-and thrive-across a wide range of ecological niches.…”

Genetic Evidence for Distinct Functions of Peptidoglycan Endopeptidases in Escherichia coli

“…The functional consequence of this redundancy remains unclear. In several studies, specific functions of PG hydrolases have been revealed (Nambu et al, 1999;Peters et al, 2016;Santin and Cascales, 2017;Murphy et al, 2019). For example, FlgJ is a lytic transglycosylase that specifically functions to form a hole in the PG that is necessary for late flagella assembly (Nambu et al, 1999).…”

Structural basis of peptidoglycan endopeptidase regulation

“…The ability of EPs to efficiently degrade PG poses an exceptional danger to cells. Indeed, purified ShyA almost completely digests purified PG sacculi in vitro (23) through its D,D-endopeptidase activity (42), and the EPs play a crucial role in cell wall degradation as a downstream consequence of exposure to β-lactam antibiotics (27,30). Interestingly, we found that overproduction of V. cholerae's two principal LysM/M23 EPs did not cause any obvious adverse growth phenotypes ( Fig.…”

“…Functional expression of both EPs was verified either by western blot (ShyA only) (SI Appendix, Fig. S1A) or via the ability to complement an EP depletion mutant (ShyA and ShyC) (42). Thus, EP-mediated PG cleavage activity is either tightly regulated in vivo or always outpaced by a highly effective cell wall synthesis machinery.…”

“…The gram-positive bacterium Bacillus subtilis (and likely other gram-positive species as well) regulates EP activity via interactions with FtsEX and the PG synthesis elongation machinery (35)(36)(37) and additionally encodes a posttranslational negative regulator, IseA (YoeB) (38), which presumably serves to tone down EP activity during cell wall stress conditions (38,39). Much less is known about EP regulation in gram-negative bacteria, where EPs appear to be kept in check as part of multiprotein complexes (40,41), at the transcriptional level (42,43), or via proteolytic degradation (44,45). Proteolytic turnover appears to be the major mode of regulation of growthpromoting EPs (44,45); however, phenotypes associated with the accumulation of EPs have surprisingly mild phenotypes under normal growth conditions, suggesting an additional unexplored layer of regulation.…”