Evolution of Acyl-Substrate Recognition by a Family of Acyl-Homoserine Lactone Synthases (original) (raw)
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Molecular Microbiology, 2004
LuxR-type transcriptional regulators play key roles in quorum-sensing systems that employ acylhomoserine lactones (acyl-HSLs) as signal molecules. These proteins mediate quorum control by changing their interactions with RNA polymerase and DNA in response to binding their cognate acyl-HSL. The evolutionarily related LuxR-type proteins exhibit considerable diversity in primary sequence and in their response to acyl-HSLs having acyl groups of differing length and composition. Little is known about which residues determine acyl-HSL specificity, and less about the evolutionary time scales required to forge new ones. To begin to examine such issues, we have focused on the LuxR protein from Vibrio fischeri , which activates gene transcription in response to binding its cognate quorum signal, 3oxohexanoyl-homoserine lactone (3OC6HSL). Libraries of lux R mutants were screened for variants exhibiting increased gene activation in response to octanoyl-HSL (C8HSL), with which wild-type LuxR interacts only weakly. Eight LuxR variants were identified that showed a 100-fold increase in sensitivity to C8HSL; these variants also displayed increased sensitivities to pentanoyl-HSL and tetradecanoyl-HSL, while maintaining a wild-type or greater response to 3OC6HSL. The most sensitive variants activated gene transcription as strongly with C8HSL as the wild type did with 3OC6HSL. With one exception, the amino acid residues involved were restricted to the N-terminal, 'signal-binding' domain of LuxR. These residue positions differed from critical positions previously identified via 'loss-of-function' mutagenesis. We have demonstrated that acyl-HSL-dependent quorumsensing systems can evolve rapidly to respond to new acyl-HSLs, suggesting that there may be an evolutionary advantage to maintaining such plasticity.
Specificity of Acyl-Homoserine Lactone Synthases Examined by Mass Spectrometry
Journal of Bacteriology, 2006
Many gram-negative bacteria produce a specific set of N-acyl-L-homoserine-lactone (AHL) signaling molecules for the purpose of quorum sensing, which is a means of regulating coordinated gene expression in a cell-density-dependent manner. AHLs are produced from acylated acyl-carrier protein (acyl-ACP) and Sadenosyl-L-methionine by the AHL synthase enzyme. The appearance of specific AHLs is due in large part to the intrinsic specificity of the enzyme for subsets of acyl-ACP substrates. Structural studies of the Pantoea stewartii enzyme EsaI and AHL-sensitive bioassays revealed that threonine 140 in the acyl chain binding pocket directs the enzyme toward production of 3-oxo-homoserine lactones. Mass spectrometry was used to examine the range of AHL molecular species produced by AHL synthases under a variety of conditions. An AHL selective normal-phase chromatographic purification with addition of a deuterated AHL internal standard was followed by reverse-phase liquid chromatography-tandem mass spectrometry in order to obtain estimates of the relative amounts of different AHLs from biological samples. The AHLs produced by wild-type and engineered EsaI and LasI AHL synthases show that intrinsic specificity and different cellular conditions influence the production of AHLs. The threonine at position 140 in EsaI is important for the preference for 3-oxo-acyl-ACPs, but the role of the equivalent threonine in LasI is less clear. In addition, LasI expressed in Escherichia coli produces a high proportion of unusual AHLs with acyl chains consisting of an odd number of carbons. Furthermore, these studies offer additional methods that will be useful for surveying and quantitating AHLs from different sources.
Acyl homoserine-lactone quorum-sensing signal generation
Proceedings of the National Academy of Sciences, 1999
Acyl homoserine lactones (acyl-HSLs) are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression. These signals are synthesized by members of the LuxI family of proteins. To understand the mechanism of acyl-HSL synthesis we have purified the Pseudomonas aeruginosa RhlI protein and analyzed the kinetics of acyl-HSL synthesis by this enzyme. Purified RhlI catalyzes the synthesis of acyl-HSLs from acyl–acyl carrier proteins and S -adenosylmethionine. An analysis of the patterns of product inhibition indicated that RhlI catalyzes signal synthesis by a sequential, ordered reaction mechanism in which S -adenosylmethionine binds to RhlI as the initial step in the enzymatic mechanism. Because pathogenic bacteria such as P. aeruginosa use acyl-HSL signals to regulate virulence genes, an understanding of the mechanism of signal synthesis and identification of inhibitors of signal synthesis has implicati...
Molecular Plant-Microbe Interactions, 1998
Many gram-negative bacteria regulate expression of specialized gene sets in response to population density. This regulatory mechanism, called autoinduction or quorumsensing, is based on the production by the bacteria of a small, diffusible signal molecule called the autoinducer. In the most well-studied systems the autoinducers are N-acylated derivatives of l-homoserine lactone (acyl-HSL). Signal specificity is conferred by the length, and the nature of the substitution at C-3, of the acyl side-chain. We evaluated four acyl-HSL bioreporters, based on tra of Agrobacterium tumefaciens, lux of Vibrio fischeri, las of Pseudomonas aeruginosa, and pigment production by Chromobacterium violaceum, for their ability to detect sets of 3-oxo acyl-HSLs, 3-hydroxy acyl-HSLs, and alkanoyl-HSLs with chain lengths ranging from C4to C12. The traG::lacZ fusion reporter from the A. tumefaciens Ti plasmid was the single most sensitive and versatile detector of the four. Using this reporter, we screened...
Journal of Biological Chemistry, 2005
Quorum sensing mediated by specific signal compounds (autoinducers) allows bacteria to monitor their cell density and enables a synchronized regulation of target gene sets. The best studied group of autoinducers are the acylhomoserine lactones (AHSLs), which are central to the regulation of virulence in many plant and animal pathogens. Variation of the acyl side chain of the AHSLs underlies the observed species specificity of this communication system. Here we show that even different strains of the plant pathogen Erwinia carotovora employ different dialects of this language and demonstrate the molecular basis for the acyl chain length specificity of distinct AHSL synthases. Under physiological concentrations, only the cognate AHSL with the "right" acyl chain is recognized as a signal that will switch on virulence genes. Mutagenesis of the AHSL synthase gene expI SCC1 identified the changes M127T and F69L as sufficient to effectively alter ExpI SCC1 (an N-3-oxohexanoyl-L-homoserine lactone producer) substrate specificity to that of an N-3-oxooctanoyl-L-homoserine lactone producer. Our data identify critical residues that define the size of the substrate-binding pocket of the AHSL synthase and will help in understanding and manipulating this bacterial language.
Small-molecule inhibitor binding to an N-acyl-homoserine lactone synthase
Quorum sensing (QS) controls certain behaviors of bacteria in response to population density. In Gram-negative bacteria, QS is often mediated by N-acyl-L-homoserine lactones (acyl-HSLs). Because QS influences the virulence of many pathogenic bacteria, synthetic inhibitors of acyl-HSL synthases might be useful therapeutically for controlling pathogens. However, rational design of a potent QS antagonist has been thwarted by the lack of information concerning the binding interactions between acyl-HSL synthases and their ligands. In the Gram-negative bacterium Burkholderia glumae, QS controls virulence, motility, and protein secretion and is mediated by the binding of N-octanoyl-L-HSL (C8-HSL) to its cognate receptor, TofR. C8-HSL is synthesized by the acyl-HSL synthase TofI. In this study, we characterized two previously unknown QS inhibitors identified in a focused library of acyl-HSL analogs. Our functional and X-ray crystal structure analyses show that the first inhibitor, J8-C8, binds to TofI, occupying the binding site for the acyl chain of the TofI cognate substrate, acylated acyl-carrier protein.
Proceedings of the National Academy of Sciences, 2005
In many Gram-negative bacteria, including a number of pathogens such as Pseudomonas aeruginosa and Erwinia carotovora, virulence factor production and biofilm formation are linked to the quorum-sensing systems that use diffusible N-acyl-L-homoserine lactones (AHLs) as intercellular messenger molecules. A number of organisms also contain genes coding for lactonases that hydrolyze AHLs into inactive products, thereby blocking the quorum-sensing systems. Consequently, these enzymes attract intense interest for the development of antiinfection therapies. However, the catalytic mechanism of AHL-lactonase is poorly understood and subject to controversy. We here report a 2.0-Å resolution structure of the AHL-lactonase from Bacillus thuringiensis and a 1.7-Å crystal structure of its complex with L-homoserine lactone. Despite limited sequence similarity, the enzyme shows remarkable structural similarities to glyoxalase II and RNase Z proteins, members of the metallo--lactamase superfamily. We present experimental evidence that AHL-lactonase is a metalloenzyme containing two zinc ions involved in catalysis, and we propose a catalytic mechanism for bacterial metallo-AHL-lactonases. quorum sensing ͉ lactonase ͉ metalloenzyme ͉ crystal structure Materials and Methods Mutagenesis, Expression, and Purification. Mutations were introduced into BTK-AiiA by using QuikChange site-directed mutagenesis (Stratagene). All proteins had the same two-residue cloning artifact (Met and Asp) at the N termini. Expression and purification are described in detail elsewhere (16). Enzyme Assay. Activity assay of BTK-AiiA was performed by using the substrate N-hexanoyl-L-homoserine lactone (C6-AHL) Conflict of interest statement: No conflicts declared. This paper was submitted directly (Track II) to the PNAS office. Freely available online through the PNAS open access option. Abbreviations: QS, quorum sensing; AHL, N-acyl-L-homoserine lactone; HSL, homoserine lactone; BTK-AiiA, AHL-lactonase from Bacillus thuringiensis subsp. kurstaki HD263; C6-AHL, N-hexanoyl-L-homoserine lactone; LC-ESI-MS, liquid chromatography electrospray ionization MS; PDB, Protein Data Bank. Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org (PDB ID codes 2BTN and 2BR6).
Structural insights into GDP-mediated regulation of a bacterial acyl-CoA thioesterase
The Journal of biological chemistry, 2017
Thioesterases catalyze the cleavage of thioester bonds within many activated fatty acids and acyl-CoA substrates. They are expressed ubiquitously in both prokaryotes and eukaryotes and are subdivided into 25 thioesterase families according to their catalytic active site, protein oligomerization, and substrate specificity. While many of these enzyme families are well characterized in terms of function and substrate specificity, regulation across most thioesterase families is poorly understood. Here, we characterized a TE6 thioesterase from the bacterium Neisseria meningitidis. Structural analysis with X-ray crystallographic diffraction data to 2.0 Å revealed that each protein subunit harbors a hot dog fold and that the TE6 enzyme forms a hexamer with D3 symmetry. An assessment of thioesterase activity against a range of acyl-CoA substrates revealed greatest activity against acetyl-CoA, and structure-guided mutagenesis of putative active site residues identified Asn-24 and Asp-39 as b...