A putative lytic transglycosylase tightly regulated and critical for the EHEC type three secretion

Abstract

Open reading frame l0045 in the pathogenic island of enterohemorrhagic Escherichia coli O157:H7 has been predicted to encode a lytic transglycosylase that is homologous to two different gene products encoded by the same bacteria at loci away from the island. To deduce the necessity of the presence in the island, we created an l0045-deleted strain of EHEC and observed that both the level of cytosolic EspA and that of the other type III secreted proteins in the media were affected. In a complementation assay, a low level-expressing L0045 appeared to recover efficiently the type III secretion (TTS). On the other hand, when l0045 was driven to express robustly, the intracellular levels of representative TTS proteins were severely suppressed. This suppression is apparently caused by the protein of L0045 per se since introducing an early translational termination codon abolished the suppression. Intriguingly, the authentic L0045 was hardly detected in all lysates of EHEC differently prepared while the same construct was expectedly expressed in the K-12 strain. A unique network must exist in EHEC to tightly regulate the presence of L0045, and we found that a LEE regulator (GrlA) is critically involved in this regulation.

Structural Analysis of a Specialized Type III Secretion System Peptidoglycan-cleaving Enzyme

“…Expression of EtgA is negatively regulated by GrlA (an activator of T3SS gene expression), presumably to allow expression of T3SS components before expression and export of EtgA to the periplasm (35). Once in the periplasm, EtgA interacts with the T3SS inner rod component EscI, which likely polymerizes into a filament.…”

“…Expression of EtgA in EHEC is negatively regulated by the presence of GrlA, an activator of T3SS gene expression (35). Presumably, this allows for synthesis of T3SS components prior to transport of EtgA to the periplasm (35). Additionally, activity of specialized PG-lytic enzymes may be spatially regulated by physical interaction with other components of the molecular transport system.…”

“…Expression of EtgA in EHEC is negatively regulated by the presence of GrlA, an activator of T3SS gene expression (35). Presumably, this allows for synthesis of T3SS components prior to transport of EtgA to the periplasm (35).…”

Type III secretion systems: the bacterial flagellum and the injectisome

“…Interestingly, many such PG lyases or muramidases are encoded within T3SS gene clusters [117][118][119][120][121] and a recent report even indicated an interaction between a lyase and the injectisome inner rod [121]. Similarly, in the flagellum, the PG lyase FlgJ has been shown to assist in the formation of the inner rod with its N-terminus, while the C-terminus exhibits a muramidase function [122,123].…”

Protein Export According to Schedule: Architecture, Assembly, and Regulation of Type III Secretion Systems from Plant- and Animal-Pathogenic Bacteria

“…To date, the contribution of predicted LTs to T3S and/or pathogenicity has been studied in both animal-and plant-pathogenic bacteria (75,192,412,413,624,625,628) (summarized in Table 3). Notably, it was observed that single LTs do not contribute significantly to T3S and virulence, presumably due to functional redundancies.…”