Peptidoglycan degradation by specialized lytic transglycosylases associated with type III and type IV secretion systems

Abstract

Specialized lytic transglycosylases are muramidases capable of locally degrading the peptidoglycan meshwork of Gram-negative bacteria. Specialized lytic transglycosylase genes are present in clusters encoding diverse macromolecular transport systems. This paper reports the analysis of selected members of the specialized lytic transglycosylase family from type III and type IV secretion systems. These proteins were analysed in vivo by assaying their ability to complement the DNA transfer defect of the conjugative F-like plasmid R1-16 lacking a functional P19 protein, the specialized lytic transglycosylase of this type IV secretion system. Heterologous complementation was accomplished using IpgF from the plasmid-encoded type III secretion system of Shigella sonnei and TrbN from the type IV secretion system of the conjugative plasmid RP4. In contrast, neither VirB1 proteins (Agrobacterium tumefaciens, Brucella suis) nor IagB (Salmonella enterica) could functionally replace P19. In vitro, IpgF, IagB, both VirB1 proteins, HP0523 (Helicobacter pylori) and P19 displayed peptidoglycanase activity in zymogram analyses. Using an established test system and a newly developed assay it was shown that IpgF degraded peptidoglycan in solution. IpgF was active only after removal of the chaperonin GroEL, which co-purified with IpgF and inhibited its enzymic activity. A mutant IpgF protein in which the predicted catalytic amino acid, Glu42, was replaced by Gln, was completely inactive. IpgF-catalysed peptidoglycan degradation was optimal at pH 6 and was inhibited by the lytic transglycosylase inhibitors hexa-N-acetylchitohexaose and bulgecin A.

How Bacteria Consume Their Own Exoskeletons (Turnover and Recycling of Cell Wall Peptidoglycan)

“…In addition, there are multiple membrane-bound lytic transglycosylases (re- viewed in reference 47). Some of these membrane-bound enzymes that cleave glycan strands are thought to serve specialized functions, such as providing space for a flagellum (31,66,102,134). Surprisingly, mutants lacking three lytic transglycosylases (SltY, MltA, and MltB) grow normally, although the rate of turnover is reduced (69).…”

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.…”

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

“…An early study that used a yeast two-hybrid assay to survey interactions between LEE encoded proteins suggested that EtgA binds the inner rod subunit, EscI (27). Peptidoglycan degrading activity of EtgA, as well as T3SS PG-lytic enzyme homologs from Salmonella and Shigella (IagB and IpgF, 41 and 35% sequence identity, respectively), was shown by zymogram, and mutation of a conserved glutamate (Glu-42 in EPEC) abrogates activity (26,28). Deletion of etgA from the EPEC homolog Citrobacter rodentium, a mouse bacterial pathogen similar to EPEC, impedes T3S and attenuates virulence (29).…”