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Zhao ZZ, Wang J, Liu X, Wang Z, Zheng X, Li W, Cheng T, Zhang J. N-acyl homoserine lactones lactonase est816 suppresses biofilm formation and periodontitis in rats mediated by Aggregatibacter actinomycetemcomitans. J Oral Microbiol 2024; 16:2301200. [PMID: 38193137 PMCID: PMC10773656 DOI: 10.1080/20002297.2023.2301200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 12/28/2023] [Indexed: 01/10/2024] Open
Abstract
Aims The current study aimed to explore the adjuvant therapeutic effect of N-acyl homoserine lactones (AHLs)-lactonase est816 on Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) biological behaviors and periodontitis progression. Methods The inhibitory properties of est816 were detected by live/dead bacterial staining, scanning electron microscope (SEM), crystal-violet staining and reverse-transcription quantitative PCR (RT-qPCR). Biocompatibility of est816 on human gingival fibroblasts (HGFs) and human gingival epithelial cells (HGEs) was evaluated by CCK8 and ELISA. The ligature-induced periodontitis model was established in rats. Micro computed tomography and immunohistochemical and histological staining served to evaluate the effect of est816 on the prevention of periodontitis in vivo. Results est816 significantly attenuated biofilm formation, reduced the mRNA expression of cytolethal distending toxin, leukotoxin and poly-N-acetyl glucosamine (PNAG) and downregulated expressions of interleukin-6 and tumor necrosis factor-α with low cell toxicity. In vivo investigations revealed est816 decreased alveolar bone resorption, suppressed matrix metalloproteinase-9 expression and increased osteoprotegerin expression. Conclusion est816 inhibited A. actinomycetemcomitans biofilm formation and virulence release, resulting in anti-inflammation and soothing of periodontitis in rats, indicating that est816 could be investigated in further research on periodontal diseases.
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Affiliation(s)
- Zelda Ziyi Zhao
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Junmin Wang
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Xinpai Liu
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Zezhi Wang
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Xianyu Zheng
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Wuli Li
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
| | - Tianfan Cheng
- Division of Periodontology & Implant Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China
| | - Jing Zhang
- Stomatological Hospital and College, Key Lab. of Oral Diseases Research of Anhui Province, Anhui Medical University, Hefei, Anhui, China
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Dai C, Qu Y, Wu W, Li S, Chen Z, Lian S, Jing J. QSP: An open sequence database for quorum sensing related gene analysis with an automatic annotation pipeline. WATER RESEARCH 2023; 235:119814. [PMID: 36934538 DOI: 10.1016/j.watres.2023.119814] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Revised: 02/18/2023] [Accepted: 02/24/2023] [Indexed: 06/18/2023]
Abstract
Quorum sensing (QS) has attracted great attention due to its important role in the bacterial interactions and its relevance to water management. With the development of high-throughput sequencing technology, a specific database for QS-related sequence annotation is urgently needed. Here, Hidden Markov Model (HMM) profiles for 38 types of QS-related proteins were built using a total of 4024 collected seed sequences. Based on both homolog search and keywords confirmation against the non-redundant database, we established a QS-related protein (QSP) database, that includes 809,721 protein sequences and 186,133 nucleotide sequences, downloaded available at: https://github.com/chunxiao-dcx/QSP. The entries were classified into 38 types and 315 subtypes among 91 bacterial phyla. Furthermore, an automatic annotation pipeline, named QSAP, was developed for rapid annotation, classification and abundance quantification of QSP-like sequences from sequencing data. This pipeline provided the two homolog alignment strategies offered by Diamond (Blastp) or HMMER (Hmmscan), as well as a data cleansing function for a subset or union set of the hits. The pipeline was tested using 14 metagenomic samples from various water environments, including activated sludge, deep-sea sediments, estuary water, and reservoir water. The QSAP pipeline is freely available for academic use in the code repository at: https://github.com/chunxiao-dcx/QSAP. The establishment of this database and pipeline, provides a useful tool for QS-related sequence annotation in a wide range of projects, and will increase our understanding of QS communication in aquatic environments.
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Affiliation(s)
- Chunxiao Dai
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Yuanyuan Qu
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
| | - Weize Wu
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Shuzhen Li
- Aquatic EcoHealth Group, Fujian Key Laboratory of Watershed Ecology, Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
| | - Zhuo Chen
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Shengyang Lian
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Jiawei Jing
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education) and Dalian POCT Laboratory, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
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Boopathi S, Ramasamy S, Haridevamuthu B, Murugan R, Veerabadhran M, Jia AQ, Arockiaraj J. Intercellular communication and social behaviors in mycobacteria. Front Microbiol 2022; 13:943278. [PMID: 36177463 PMCID: PMC9514802 DOI: 10.3389/fmicb.2022.943278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 08/22/2022] [Indexed: 11/13/2022] Open
Abstract
Cell-to-cell communication is a fundamental process of bacteria to exert communal behaviors. Sputum samples of patients with cystic fibrosis have often been observed with extensive mycobacterial genetic diversity. The emergence of heterogenic mycobacterial populations is observed due to subtle changes in their morphology, gene expression level, and distributive conjugal transfer (DCT). Since each subgroup of mycobacteria has different hetero-resistance, they are refractory against several antibiotics. Such genetically diverse mycobacteria have to communicate with each other to subvert the host immune system. However, it is still a mystery how such heterogeneous strains exhibit synchronous behaviors for the production of quorum sensing (QS) traits, such as biofilms, siderophores, and virulence proteins. Mycobacteria are characterized by division of labor, where distinct sub-clonal populations contribute to the production of QS traits while exchanging complimentary products at the community level. Thus, active mycobacterial cells ensure the persistence of other heterogenic clonal populations through cooperative behaviors. Additionally, mycobacteria are likely to establish communication with neighboring cells in a contact-independent manner through QS signals. Hence, this review is intended to discuss our current knowledge of mycobacterial communication. Understanding mycobacterial communication could provide a promising opportunity to develop drugs to target key pathways of mycobacteria.
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Affiliation(s)
- Seenivasan Boopathi
- Key Laboratory of Tropical Biological Resources of Ministry Education, School of Pharmaceutical Sciences, Hainan University, Haikou, China
- Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Chennai, Tamil Nadu, India
| | - Subbiah Ramasamy
- Department of Biochemistry, Cardiac Metabolic Disease Laboratory, School of Biological Sciences, Madurai Kamaraj University, Madurai, India
| | - B. Haridevamuthu
- Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Chennai, Tamil Nadu, India
| | - Raghul Murugan
- Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Chennai, Tamil Nadu, India
| | - Maruthanayagam Veerabadhran
- Biofouling and Biofilm Processes Section, Water and Steam Chemistry Division, Bhabha Atomic Research Centre Facilities, Kalpakkam, Tamil Nadu, India
| | - Ai-Qun Jia
- Key Laboratory of Tropical Biological Resources of Ministry Education, School of Pharmaceutical Sciences, Hainan University, Haikou, China
- *Correspondence: Ai-Qun Jia
| | - Jesu Arockiaraj
- Department of Biotechnology, College of Science and Humanities, SRM Institute of Science and Technology, Chennai, Tamil Nadu, India
- Jesu Arockiaraj ;
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Ernst S, Volkov AN, Stark M, Hölscher L, Steinert K, Fetzner S, Hennecke U, Drees SL. Azetidomonamide and Diazetidomonapyridone Metabolites Control Biofilm Formation and Pigment Synthesis in Pseudomonas aeruginosa. J Am Chem Soc 2022; 144:7676-7685. [PMID: 35451837 DOI: 10.1021/jacs.1c13653] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Synthesis of azetidine-derived natural products by the opportunistic pathogen Pseudomonas aeruginosa is controlled by quorum sensing, a process involving the production and sensing of diffusible signal molecules that is decisive for virulence regulation. In this study, we engineered P. aeruginosa for the titratable expression of the biosynthetic aze gene cluster, which allowed the purification and identification of two new products, azetidomonamide C and diazetidomonapyridone. Diazetidomonapyridone was shown to have a highly unusual structure with two azetidine rings and an open-chain diimide moiety. Expression of aze genes strongly increased biofilm formation and production of phenazine and alkyl quinolone virulence factors. Further physiological studies revealed that all effects were mainly mediated by azetidomonamide A and diazetidomonapyridone, whereas azetidomonamides B and C had little or no phenotypic impact. The P450 monooxygenase AzeF which catalyzes a challenging, stereoselective hydroxylation of the azetidine ring converting azetidomonamide C into azetidomonamide A is therefore crucial for biological activity. Based on our findings, we propose this group of metabolites to constitute a new class of diffusible regulatory molecules with community-related effects in P. aeruginosa.
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Affiliation(s)
- Simon Ernst
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstr. 3, Münster 48149, Germany
| | - Alexander N Volkov
- VIB Centre for Structural Biology, Vlaams Instituut voor Biotechnologie (VIB), Pleinlaan 2, Brussels 1050, Belgium.,Jean Jeener NMR Centre, Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels 1050 Belgium
| | - Melina Stark
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstr. 3, Münster 48149, Germany
| | - Lea Hölscher
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstr. 3, Münster 48149, Germany
| | - Katharina Steinert
- Institute for Food Chemistry, University of Münster, Corrensstr. 45, Münster 48149, Germany
| | - Susanne Fetzner
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstr. 3, Münster 48149, Germany
| | - Ulrich Hennecke
- Organic Chemistry Research Group, Department of Chemistry and Department of Bioengineering Sciences, Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels 1050, Belgium
| | - Steffen Lorenz Drees
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstr. 3, Münster 48149, Germany
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Arranz San Martín A, Vogel J, Wullich SC, Quax WJ, Fetzner S. Enzyme-Mediated Quenching of the Pseudomonas Quinolone Signal (PQS): A Comparison between Naturally Occurring and Engineered PQS-Cleaving Dioxygenases. Biomolecules 2022; 12:biom12020170. [PMID: 35204671 PMCID: PMC8961568 DOI: 10.3390/biom12020170] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 01/13/2022] [Accepted: 01/18/2022] [Indexed: 02/06/2023] Open
Abstract
The opportunistic pathogen Pseudomonas aeruginosa employs quorum sensing to govern the production of many virulence factors. Interference with quorum sensing signaling has therefore been put forward as an attractive approach to disarm this pathogen. Here, we analyzed the quorum quenching properties of natural and engineered (2-alkyl-)3-hydroxy-4(1H)-quinolone 2,4-dioxygenases (HQDs) that inactivate the P. aeruginosa signal molecule PQS (Pseudomonas quinolone signal; 2-heptyl-3-hydroxy-4(1H)-quinolone). When added exogenously to P. aeruginosa cultures, all HQDs tested significantly reduced the levels of PQS and other alkylquinolone-type secondary metabolites deriving from the biosynthetic pathway, such as the respiratory inhibitor 2-heptyl-4-hydroxyquinoline N-oxide. HQDs from Nocardia farcinica and Streptomyces bingchenggensis, which combine low KM values for PQS with thermal stability and resilience in the presence of P. aeruginosa exoproducts, respectively, attenuated production of the virulence factors pyocyanin and pyoverdine. A delay in mortality was observed when Galleria mellonella larvae were infected with P. aeruginosa suspensions treated with the S. bingchenggensis HQD or with inhibitors of alkylquinolone biosynthesis. Our data indicate that quenching of PQS signaling has potential as an anti-virulence strategy; however, an efficient anti-virulence therapy against P. aeruginosa likely requires a combination of agents addressing multiple targets.
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Affiliation(s)
- Alba Arranz San Martín
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstraße 3, 48149 Münster, Germany; (A.A.S.M.); (S.C.W.)
| | - Jan Vogel
- Department of Chemical and Pharmaceutical Biology, Groningen Research Institute of Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands; (J.V.); (W.J.Q.)
| | - Sandra C. Wullich
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstraße 3, 48149 Münster, Germany; (A.A.S.M.); (S.C.W.)
| | - Wim J. Quax
- Department of Chemical and Pharmaceutical Biology, Groningen Research Institute of Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands; (J.V.); (W.J.Q.)
| | - Susanne Fetzner
- Institute for Molecular Microbiology and Biotechnology, University of Münster, Corrensstraße 3, 48149 Münster, Germany; (A.A.S.M.); (S.C.W.)
- Correspondence: ; Tel.: +49-251-83-39824
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Wullich SC, Wijma HJ, Janssen DB, Fetzner S. Stabilizing AqdC, a Pseudomonas Quinolone Signal-Cleaving Dioxygenase from Mycobacteria, by FRESCO-Based Protein Engineering. Chembiochem 2021; 22:733-742. [PMID: 33058333 PMCID: PMC7894191 DOI: 10.1002/cbic.202000641] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 10/13/2020] [Indexed: 12/11/2022]
Abstract
The mycobacterial PQS dioxygenase AqdC, a cofactor-less protein with an α/β-hydrolase fold, inactivates the virulence-associated quorum-sensing signal molecule 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) produced by the opportunistic pathogen Pseudomonas aeruginosa and is therefore a potential anti-virulence tool. We have used computational library design to predict stabilizing amino acid replacements in AqdC. While 57 out of 91 tested single substitutions throughout the protein led to stabilization, as judged by increases in T app m of >2 °C, they all impaired catalytic activity. Combining substitutions, the proteins AqdC-G40K-A134L-G220D-Y238W and AqdC-G40K-G220D-Y238W showed extended half-lives and the best trade-off between stability and activity, with increases in T app m of 11.8 and 6.1 °C and relative activities of 22 and 72 %, respectively, compared to AqdC. Molecular dynamics simulations and principal component analysis suggested that stabilized proteins are less flexible than AqdC, and the loss of catalytic activity likely correlates with an inability to effectively open the entrance to the active site.
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Affiliation(s)
- Sandra C. Wullich
- Institut für Molekulare Mikrobiologie und BiotechnologieWWU MünsterCorrensstraße 348149 MünsterGermany
| | - Hein J. Wijma
- Department of Biochemistry Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenNijenborgh 49747 AGGroningen (TheNetherlands
| | - Dick B. Janssen
- Department of Biochemistry Groningen Biomolecular Sciences and Biotechnology InstituteUniversity of GroningenNijenborgh 49747 AGGroningen (TheNetherlands
| | - Susanne Fetzner
- Institut für Molekulare Mikrobiologie und BiotechnologieWWU MünsterCorrensstraße 348149 MünsterGermany
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Thi MTT, Wibowo D, Rehm BH. Pseudomonas aeruginosa Biofilms. Int J Mol Sci 2020; 21:ijms21228671. [PMID: 33212950 PMCID: PMC7698413 DOI: 10.3390/ijms21228671] [Citation(s) in RCA: 283] [Impact Index Per Article: 70.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 11/09/2020] [Accepted: 11/13/2020] [Indexed: 12/17/2022] Open
Abstract
Pseudomonas aeruginosa is an opportunistic human pathogen causing devastating acute and chronic infections in individuals with compromised immune systems. Its highly notorious persistence in clinical settings is attributed to its ability to form antibiotic-resistant biofilms. Biofilm is an architecture built mostly by autogenic extracellular polymeric substances which function as a scaffold to encase the bacteria together on surfaces, and to protect them from environmental stresses, impedes phagocytosis and thereby conferring the capacity for colonization and long-term persistence. Here we review the current knowledge on P. aeruginosa biofilms, its development stages, and molecular mechanisms of invasion and persistence conferred by biofilms. Explosive cell lysis within bacterial biofilm to produce essential communal materials, and interspecies biofilms of P. aeruginosa and commensal Streptococcus which impedes P. aeruginosa virulence and possibly improves disease conditions will also be discussed. Recent research on diagnostics of P. aeruginosa infections will be investigated. Finally, therapeutic strategies for the treatment of P. aeruginosa biofilms along with their advantages and limitations will be compiled.
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Sikdar R, Elias M. Quorum quenching enzymes and their effects on virulence, biofilm, and microbiomes: a review of recent advances. Expert Rev Anti Infect Ther 2020; 18:1221-1233. [PMID: 32749905 DOI: 10.1080/14787210.2020.1794815] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
INTRODUCTION Numerous bacterial behaviors are regulated by a cell-density dependent mechanism known as Quorum Sensing (QS). QS relies on communication between bacterial cells using diffusible signaling molecules known as autoinducers. QS regulates physiological processes such as metabolism, virulence, and biofilm formation. Quorum Quenching (QQ) is the inhibition of QS using chemical or enzymatic means to counteract behaviors regulated by QS. AREAS COVERED We examine the main, diverse QS mechanisms present in bacterial species, with a special emphasis on AHL-mediated QS. We also discuss key in vitro and in vivo systems in which interference in QS was investigated. Additionally, we highlight promising developments, such as the substrate preference of the used enzymatic quencher, in the application of interference in QS to counter bacterial virulence. EXPERT OPINION Enabled via the recent isolation of highly stable quorum quenching enzymes and/or molecular engineering efforts, the effects of the interference in QS were recently evaluated outside of the traditional model of single species culture. Signal disruption in complex microbial communities was shown to result in the disruption of complex microbial behaviors, and changes in population structures. These new findings, and future studies, may result in significant changes in the traditional views about QS.
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Affiliation(s)
- Rakesh Sikdar
- Biochemistry, Molecular Biology & Biophysics Department and BioTechnology Institute, University of Minnesota , Saint Paul, Minnesota, USA
| | - Mikael Elias
- Biochemistry, Molecular Biology & Biophysics Department and BioTechnology Institute, University of Minnesota , Saint Paul, Minnesota, USA
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An α/β-Hydrolase Fold Subfamily Comprising Pseudomonas Quinolone Signal-Cleaving Dioxygenases. Appl Environ Microbiol 2020; 86:AEM.00279-20. [PMID: 32086305 DOI: 10.1128/aem.00279-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 02/12/2020] [Indexed: 01/25/2023] Open
Abstract
The quinolone ring is a common core structure of natural products exhibiting antimicrobial, cytotoxic, and signaling activities. A prominent example is the Pseudomonas quinolone signal (PQS), a quorum-sensing signal molecule involved in the regulation of virulence of Pseudomonas aeruginosa The key reaction to quinolone inactivation and biodegradation is the cleavage of the 3-hydroxy-4(1H)-quinolone ring, catalyzed by dioxygenases (HQDs), which are members of the α/β-hydrolase fold superfamily. The α/β-hydrolase fold core domain consists of a β-sheet surrounded by α-helices, with an active site usually containing a catalytic triad comprising a nucleophilic residue, an acidic residue, and a histidine. The nucleophile is located at the tip of a sharp turn, called the "nucleophilic elbow." In this work, we developed a search workflow for the identification of HQD proteins from databases. Search and validation criteria include an [H-x(2)-W] motif at the nucleophilic elbow, an [HFP-x(4)-P] motif comprising the catalytic histidine, the presence of a helical cap domain, the positioning of the triad's acidic residue at the end of β-strand 6, and a set of conserved hydrophobic residues contributing to the substrate cavity. The 161 candidate proteins identified from the UniProtKB database originate from environmental and plant-associated microorganisms from all domains of life. Verification and characterization of HQD activity of 9 new candidate proteins confirmed the reliability of the search strategy and suggested residues correlating with distinct substrate preferences. Among the new HQDs, PQS dioxygenases from Nocardia farcinica, N. cyriacigeorgica, and Streptomyces bingchenggensis likely are part of a catabolic pathway for alkylquinolone utilization.IMPORTANCE Functional annotation of protein sequences is a major requirement for the investigation of metabolic pathways and the identification of sought-after biocatalysts. To identify heterocyclic ring-cleaving dioxygenases within the huge superfamily of α/β-hydrolase fold proteins, we defined search and validation criteria for the primarily motif-based identification of 3-hydroxy-4(1H)-quinolone 2,4-dioxygenases (HQD). HQDs are key enzymes for the inactivation of metabolites, which can have signaling, antimicrobial, or cytotoxic functions. The HQD candidates detected in this study occur particularly in environmental and plant-associated microorganisms. Because HQDs active toward the Pseudomonas quinolone signal (PQS) likely contribute to interactions within microbial communities and modulate the virulence of Pseudomonas aeruginosa, we analyzed the catalytic properties of a PQS-cleaving subset of HQDs and specified characteristics to identify PQS-cleaving dioxygenases within the HQD family.
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