Recent progresses on synthesized LuxS inhibitors: A mini-review

Design and synthesis of LuxS enzyme inhibitors otherwise known as S-ribosylhomocysteine analogues, to target quorum sensing in bacteria, has been considerably developed within the last decade. This review presents which molecules have been synthesized to target LuxS enzyme in other words inhibitors of S-ribosylhomocysteinase. It reports their tested biological activity as LuxS inhibitors when available. A systematic overview has been conducted by searching PubMed, Medline, and The Cochrane Library and data extraction of all synthesized S-ribosylhomocysteine analogues has been collected. This mini-review shows limited data to date on this area and should continue to be studied.     

乳酸菌群体感应与其肠道生物膜形成的研究进展

肠道内栖息着数量庞大且复杂的微生物菌群,是一个具有生物多样性的微环境,菌群在调节宿主肠道健康中发挥着重要作用。群体感应(quorumsensing,QS)是细菌间通过化学信号分子进行信息传递的重要方式。本文综述了QS系统组成、信号转导机制及AI-2/LuxS系统对肠道生物膜形成的调控,介绍了乳酸菌AI-2/LuxSQS系统及其在调控生物膜形成上的作用。通过肠道乳酸菌QS与生物膜形成综述分析,旨在为肠道屏障功能和健康调控提供新思路。     

Let LuxS speak up in AI-2 signaling

Quorum sensing is a process of bacterial cell-cell communication that uses small diffusible molecules to coordinate diverse behaviors in response to population density. The only quorum-sensing system shared by Gram-positive and Gram-negative bacteria involves the production of autoinducer-2 (AI-2). The AI-2 synthase LuxS is widely distributed among the Bacteria, which suggests that AI-2 is a language for interspecies communication. However, LuxS is also an integral component of the activated methyl cycle in bacteria. LuxS-based quorum sensing has been intensively studied in the past decade, mostly in relation to the AI-2 molecule and the downstream effects of luxS knockouts; few studies have focused on the gene and protein activity itself. Ongoing attempts to dissect the metabolic and signaling roles of LuxS leave little doubt that unraveling the regulation of luxS expression and cellular LuxS activity is the key to understanding LuxS-based quorum sensing.     

Identification of a key amino acid of LuxS involved in AI-2 production in Campylobacter jejuni

Autoinducer-2 (AI-2) mediated quorum sensing has been associated with the expression of virulence factors in a number of pathogenic organisms and has been demonstrated to play a role in motility and cytolethal distending toxin (cdt) production in Campylobacter jejuni. We have initiated the work to determine the molecular basis of AI-2 synthesis and the biological functions of quorum sensing in C. jejuni. In this work, two naturally occurring variants of C. jejuni 81116 were identified, one producing high-levels of AI-2 while the other is defective in AI-2 synthesis. Sequence analysis revealed a G92D mutation in the luxS gene of the defective variant. Complementation of the AI-2(-) variant with a plasmid encoded copy of the wild-type luxS gene or reversion of the G92D mutation by site-directed mutagenesis fully restored AI-2 production by the variant. These results indicate that the G92D mutation alone is responsible for the loss of AI-2 activity in C. jejuni. Kinetic analyses showed that the G92D LuxS has a ～100-fold reduced catalytic activity relative to the wild-type enzyme. Findings from this study identify a previously undescribed amino acid that is essential for AI-2 production by LuxS and provide a unique isogenic pair of naturally occurring variants for us to dissect the functions of AI-2 mediated quorum sensing in Campylobacter.     

The small regulatory RNA molecule MicA is involved in <Emphasis Type="Italic">Salmonella enterica</Emphasis> serovar Typhimurium biofilm formation

Background  

LuxS is the synthase enzyme of the quorum sensing signal AI-2. In Salmonella Typhimurium, it was previously shown that a luxS deletion mutant is impaired in biofilm formation. However, this phenotype could not be complemented by extracellular addition of quorum sensing signal molecules.     

In <Emphasis Type="Italic">Helicobacter pylori</Emphasis> auto-inducer-2, but not LuxS/MccAB catalysed reverse transsulphuration,regulates motility through modulation of flagellar gene transcription

Background  

LuxS may function as a metabolic enzyme or as the synthase of a quorum sensing signalling molecule, auto-inducer-2 (AI-2); hence, the mechanism underlying phenotypic changes upon luxS inactivation is not always clear. In Helicobacter pylori, we have recently shown that, rather than functioning in recycling methionine as in most bacteria, LuxS (along with newly-characterised MccA and MccB), synthesises cysteine via reverse transsulphuration. In this study, we investigated whether and how LuxS controls motility of H. pylori, specifically if it has its effects via luxS-required cysteine metabolism or via AI-2 synthesis only.     

Bacterial cell-to-cell communication: sorry, can't talk now - gone to lunch!

The identification of novel bacterial cell-to-cell communication (quorum sensing) systems based on diffusible signal molecules, such as indole and the LuxS autoinducer-2, requires discrimination between true signalling molecules and metabolites present in culture supernatants. This depends on rigorous chemical characterisation and demonstration that the molecule controls cellular responses beyond those required to metabolise or detoxify the signal.     

2D proteome analysis initiates new Insights on the Salmonella Typhimurium LuxS protein

Background  

Quorum sensing is a term describing a bacterial communication system mediated by the production and recognition of small signaling molecules. The LuxS enzyme, catalyzing the synthesis of AI-2, is conserved in a wide diversity of bacteria. AI-2 has therefore been suggested as an interspecies quorum sensing signal. To investigate the role of endogenous AI-2 in protein expression of the Gram-negative pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium), we performed a 2D-DIGE proteomics experiment comparing total protein extract of wildtype S. Typhimurium with that of a luxS mutant, unable to produce AI-2.     

Mechanism of action of S-ribosylhomocysteinase (LuxS)

S-Ribosylhomocysteinase (LuxS) cleaves the thioether bond in S-ribosylhomocysteine to produce homocysteine and 4,5-dihydroxy-2,3-pentanedione. This reaction serves the dual purposes of detoxification of S-adenosylhomocysteine and production of type 2 quorum sensing molecule. Recent research has shown that LuxS uses Fe(2+) to catalyze an internal redox reaction, shifting the ribose carbonyl group from its C1 to C3 position. Subsequent beta-elimination completes this highly unusual reaction. LuxS and other enzymes on the same pathway may provide a novel class of antibacterial drug targets.     

群体感应信号分子AI-2研究进展

群体感应(QS)是细菌根据种群密度的变化调控基因表达,协调群体行为的机制。除具有种特异性的信号分子AI-1外,近年来发现一类新的信号分子AI-2在调控细菌基因表达中起重要作用。AI-2的结构和生物合成途径已被确定,其产生依赖于一种称为LuxS的蛋白。目前认为AI-2在细菌种间交流中起通用信号分子(universalsignal)的作用。了解细菌的QS调控过程以及种间细胞交流的新机制,有助于对细菌病害进行防治。     

A structural genomics approach to the study of quorum sensing: crystal structures of three LuxS orthologs.

BACKGROUND: Quorum sensing is the mechanism by which bacteria control gene expression in response to cell density. Two major quorum-sensing systems have been identified, system 1 and system 2, each with a characteristic signaling molecule (autoinducer-1, or AI-1, in the case of system 1, and AI-2 in system 2). The luxS gene is required for the AI-2 system of quorum sensing. LuxS and AI-2 have been described in both Gram-negative and Gram-positive bacterial species and have been shown to be involved in the expression of virulence genes in several pathogens. RESULTS: The structure of the LuxS protein from three different bacterial species with resolutions ranging from 1.8 A to 2.4 A has been solved using an X-ray crystallographic structural genomics approach. The structure of LuxS reported here is seen to have a new alpha-beta fold. In all structures, an equivalent homodimer is observed. A metal ion identified as zinc was seen bound to a Cys-His-His triad. Methionine was found bound to the protein near the metal and at the dimer interface. CONCLUSIONS: These structures provide support for a hypothesis that explains the in vivo action of LuxS. Specifically, acting as a homodimer, the protein binds a methionine analog, S-ribosylhomocysteine (SRH). The zinc atom is in position to cleave the ribose ring in a step along the synthesis pathway of AI-2.     

A naturally occurring brominated furanone covalently modifies and inactivates LuxS

Halogenated furanones, a group of natural products initially isolated from marine red algae, are known to inhibit bacterial biofilm formation, swarming, and quorum sensing. However, their molecular targets and the precise mode of action remain elusive. Herein, we show that a naturally occurring brominated furanone covalently modifies and inactivates LuxS (S-ribosylhomocysteine lyase, EC 4.4.1.21), the enzyme which produces autoinducer-2 (AI-2).     

The <Emphasis Type="Italic">luxS</Emphasis> Gene Is Involved in AI-2 Production,Pathogenicity, and Some Phenotypes in <Emphasis Type="Italic">Erwinia amylovora</Emphasis>

Erwinia amylovora causes fire blight of apple, pear, and other members of the Rosaceae family. The enzyme LuxS catalyzes the last step in the production of autoinducer-2 (AI-2), a molecule implicated with quorum sensing in many bacterial species. It is now well recognized that LuxS also plays a central role in sulfur metabolism and in the activated methyl cycle, which is responsible for the generation of S-adenosyl-l-methionine. A research paper has reported that luxS is not involved with quorum sensing in Er. amylovora, but in our study, Er. amylovora strain NCPPB1665 (Ea1665) produced luxS-dependent extracellular AI-2 activity. Additionally, the maximal AI-2 activity occurred during late-exponential and early-stationary growth phases and diminished during the stationary phase. The luxS mutant of Ea1665 was constructed, and the phenotypes of a defined luxS mutant have been characterized. Inactivation of luxS in Ea1665 impaired motility, extracellular polysaccharide (EPS) production, and tolerance for hydrogen peroxide, and reduced virulence on pear leaves. Yan Gao and Junxian Song contributed equally to this research.     

乳酸菌与酵母菌共生机理的研究进展

早期研究者从营养角度分析乳酸菌与酵母菌的共生机制,发现混合培养过程中乳酸菌与酵母菌不仅存在互补机制,代谢产物相互之间能够产生促进或抑制作用。随着Lux S/AI-2介导的群体感应现象(QS)的发现与发展,目前研究者多从群体感应角度来探讨乳酸菌与酵母菌种间的信息交流模式。本文着重从营养及信号分子这两个角度阐述目前乳酸菌与酵母菌共生机理的研究进展。     

Effect of Homocysteine on Biofilm Formation by Mycobacteria

Mycobacteria show peculiar aggregated outgrowth like biofilm on the surface of solid or liquid media. Biofilms harbor antibiotic resistant bacteria in a self-produced extracellular matrix that signifies the bacterial fate to sedentary existence. Despite years of research, very little is known about the mechanisms that contribute to biofilm formation. LuxS has been previously known to play a role in biofilm formation in Autoinducer-2 dependent manner. We here show the effect of LuxS product-homocysteine, on the biofilm forming ability of non-tuberculous mycobacteria, Mycobacterium smegmatis and Mycobacterium bovis BCG showing AI-2 independent phenotypic effect of LuxS. Exogenous supplementation of homocysteine in the culture media leads to aberrant cording, pellicle outgrowth, and biofilm formation. Thus, our study contributes to the better understanding of the mechanism of mycobacterial biofilm formation and sheds light on the role of LuxS product homocysteine. In addition, we highlight the contribution of activated methyl cycle in bacterial quorum sensing.     

Quorum sensing by the Lyme disease spirochete

The Lyme disease spirochete, Borrelia burgdorferi, utilizes a LuxS/autoinducer-2-dependent quorum sensing mechanism to control a specific subset of bacterial proteins. It is hypothesized that this system facilitates transmission of B. burgdorferi from feeding ticks into warm-blooded hosts.     

Lack of genomic evidence of AI-2 receptors suggests a non-quorum sensing role for <Emphasis Type="Italic">luxS</Emphasis> in most bacteria

Background  

Great excitement accompanied discoveries over the last decade in several Gram-negative and Gram-positive bacteria of the LuxS protein, which catalyzes production of the AI-2 autoinducer molecule for a second quorum sensing system (QS-2). Since the luxS gene was found to be widespread among the most diverse bacterial taxa, it was hypothesized that AI-2 may constitute the basis of a universal microbial language, a kind of bacterial Esperanto. Many of the studies published in this field have drawn a direct correlation between the occurrence of the luxS gene in a given organism and the presence and functionality of a QS-2 therein. However, rarely hathe existence of potential AI-2 receptors been examined. This is important, since it is now well recognized that LuxS also holds a central role as a metabolic enzyme in the activated methyl cycle which is responsible for the generation of S-adenosyl-L-methionine, the major methyl donor in the cell.