Anti-infectious Effect of S-Benzylisothiourea Compound A22, Which Inhibits the Actin-Like Protein, MreB, in Shigella flexneri

Abstract

Various antibacterial agents have been developed and used for the treatment and prevention of infectious diseases. These drugs show antibacterial activity by inhibiting growth or directly killing bacteria. This antibacterial activity induces the microbial substitution and the emergence of drug-resistant bacteria.1) Therefore, improper use of antibacterial agents selects for drug-resistant bacteria and increases their prevalence. To prevent this problem, it is necessary to develop therapeutic agents that are fundamentally different from current antibacterial agents.2) It is possible that prevention or blockage of bacterial infections could be achieved by interfering with the adherence and/or the invasion of bacteria in host cells. The type III secretion apparatus, one of the virulence factors in bacteria, is necessary for the invasion of pathogenic bacteria into host cells. [3][4][5] Preventing the function of the type III secretion apparatus can attenuate the infectious capacity of pathogenic bacteria, including Yersinia 6) and Chlamydia, 7) without actually killing of the bacteria. Therefore, the type III apparatus has been considered a candidate target site for the development of new antibacterial agents. 8,9) Actin-like protein, MreB, which serves a cytoskeletal function, is necessary for maintenance of the rod-shape of bacteria, including Escherichia coli and Bacillus subtilis. [10][11][12] Furthermore, MreB is associated with chromosome segregation and protein localization to the cell poles.13-15) S-(3,4-Dichlorobenzyl)isothiourea (A22), which was discovered as an inhibitor of replication in E. coli, inhibits the function of MreB by binding to MreB and transforming rod-shaped bacterial cells into coccoid forms. 13,16) A22 has a bacteriostatic effect on certain Gram-negative bacilli, including E. coli. 16)Shigella spp., which are Gram-negative rod-shaped bacteria, are some of the causative agents of bacillary dysentery. 17)Via oral ingestion, Shigella reaches the colon and invades the intestinal epithelial cells, causing destruction of the epithelial layer. The type III secretion system is necessary for the invasion of Shigella into epithelial cells and it delivers effectors directly into host cells. 17,18) The secreted effectors identified in S. flexneri are virulence factors for host cells and various type III effectors, including IpaA, IpaB, IpaC, IpaD, IpgD, and VirA. [18][19][20] Type III secretion systems are not found in non-pathogens. Furthermore, in addition to the type III secretion system, the rod-shape of Shigella seems likely to be necessary for the invasion of host cells because the shape of the cells is linked to the polar localization of certain proteins, including IcsA. 15,21) In this study, the antibacterial activity of A22 was determined, in addition to its coccoid form-inducing effects. Furthermore, the infectious capacity and effector secretion of A22-induced coccoid Shigella cells were examined. We suggest the utility of A22 as a lead compound for generating new anti-infectious drugs an...

Deciphering Morphological Determinants of the Helix-Shaped Leptospira

“…L. biflexa MreB shares 50 to 60% identity with MreB from E. coli or C. crescentus. To understand the role of MreB, we first used the A22 compound, which has been shown to affect the function and to mimic loss of this actin-like homologue in several Gram-negative microorganisms (5,20,41). Figure 4 shows that cells treated with A22 at concentrations around the MIC level presented a phenotype similar to what we observed when they were subjected to penicillin G. Morphological changes appeared after 8 h. The growth rate was comparable to that of the control cells until 8 h after addition of the compound, and then the cells stopped growing and started lysing 12 h after addition of A22.…”

MreB Drives De N ovo Rod Morphogenesis in Caulobacter crescentus via Remodeling of the Cell Wall

“…A22 has been used to reversibly disrupt the localization and function of MreB in C. crescentus and other Gramnegative bacteria (23,32,41,45,52). However, A22 is known to reduce the growth rate of an E. coli mutant that lacks MreB at concentrations of 50 g/ml (212 M) and higher (35), suggesting that A22 inhibits cellular function(s) other than that of MreB.…”

“…To examine how MreB can drive de novo rod shape morphogenesis, we followed a similar strategy except that we used drug treatment to interfere with MreB function. The small molecule 3,4-dichlorobenzyl carbamimidothioate, also known as A22, has been shown to rapidly disrupt MreB localization in vivo and to induce growth-dependent rounding in several Gram-negative bacteria (23,32,41,45,52). Furthermore, genetic and biochemical experiments have shown that MreB is the direct molecular target of A22 and that A22 binds to MreB's ATP-binding pocket, inducing a state with low affinity for polymerization (3,23).…”

Anti-<i>Pseudomonas aeruginosa</i> Compound, 1,2,3,4-Tetrahydro-1,3,5-triazine Derivative, Exerts Its Action by Primarily Targeting MreB

“…5) In addition, A22 has a bacteriostatic effect on E. coli and Shigella flexneri. 5,6) Several groups found some derivatives with similar antibacterial activity against some bacteria through the investigation of structure-activity relationship of A22 derivatives. 7,8) However, all these derivatives thus far were modified on benzyl ring, not isothiourea.…”