1
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Kumar A, Chakravorty S, Yang T, Russo TA, Newton SM, Klebba PE. Siderophore-mediated iron acquisition by Klebsiella pneumoniae. J Bacteriol 2024; 206:e0002424. [PMID: 38591913 PMCID: PMC11112993 DOI: 10.1128/jb.00024-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 03/05/2024] [Indexed: 04/10/2024] Open
Abstract
Microbes synthesize and secrete siderophores, that bind and solubilize precipitated or otherwise unavailable iron in their microenvironments. Gram (-) bacterial TonB-dependent outer membrane receptors capture the resulting ferric siderophores to begin the uptake process. From their similarity to fepA, the structural gene for the Escherichia coli ferric enterobactin (FeEnt) receptor, we identified four homologous genes in the human and animal ESKAPE pathogen Klebsiella pneumoniae (strain Kp52.145). One locus encodes IroN (locus 0027 on plasmid pII), and three other loci encode other FepA orthologs/paralogs (chromosomal loci 1658, 2380, and 4984). Based on the crystal structure of E. coli FepA (1FEP), we modeled the tertiary structures of the K. pneumoniae FepA homologs and genetically engineered individual Cys substitutions in their predicted surface loops. We subjected bacteria expressing the Cys mutant proteins to modification with extrinsic fluorescein maleimide (FM) and used the resulting fluorescently labeled cells to spectroscopically monitor the binding and transport of catecholate ferric siderophores by the four different receptors. The FM-modified FepA homologs were nanosensors that defined the ferric catecholate uptake pathways in pathogenic strains of K. pneumoniae. In Kp52.145, loci 1658 and 4984 encoded receptors that primarily recognized and transported FeEnt; locus 0027 produced a receptor that principally bound and transported FeEnt and glucosylated FeEnt (FeGEnt); locus 2380 encoded a protein that bound ferric catecholate compounds but did not detectably transport them. The sensors also characterized the uptake of iron complexes, including FeGEnt, by the hypervirulent, hypermucoviscous K. pneumoniae strain hvKp1. IMPORTANCE Both commensal and pathogenic bacteria produce small organic chelators, called siderophores, that avidly bind iron and increase its bioavailability. Klebsiella pneumoniae variably produces four siderophores that antagonize host iron sequestration: enterobactin, glucosylated enterobactin (also termed salmochelin), aerobactin, and yersiniabactin, which promote colonization of different host tissues. Abundant evidence links bacterial iron acquisition to virulence and infectious diseases. The data we report explain the recognition and transport of ferric catecholates and other siderophores, which are crucial to iron acquisition by K. pneumoniae.
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Affiliation(s)
- Ashish Kumar
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
- Department of Rare Blood and Musculoskeletal Disorders, Sanofi, Cambridge, Massachusetts, USA
| | - Somnath Chakravorty
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
- Jacobs School of Medicine, University at Buffalo, Buffalo, New York, USA
| | - Taihao Yang
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Thomas A. Russo
- Jacobs School of Medicine, University at Buffalo, Buffalo, New York, USA
- Veterans Administration, Western New York Healthcare System, Buffalo, New York, USA
| | - Salete M. Newton
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Phillip E. Klebba
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
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2
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Vogt LN, Panis G, Schäpers A, Peschek N, Huber M, Papenfort K, Viollier PH, Fröhlich KS. Genome-wide profiling of Hfq-bound RNAs reveals the iron-responsive small RNA RusT in Caulobacter crescentus. mBio 2024; 15:e0315323. [PMID: 38511926 PMCID: PMC11005374 DOI: 10.1128/mbio.03153-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 02/28/2024] [Indexed: 03/22/2024] Open
Abstract
The alphaproteobacterium Caulobacter crescentus thrives in oligotrophic environments and is able to optimally exploit minimal resources by entertaining an intricate network of gene expression control mechanisms. Numerous transcriptional activators and repressors have been reported to contribute to these processes, but only few studies have focused on regulation at the post-transcriptional level in C. crescentus. Small RNAs (sRNAs) are a prominent class of regulators of bacterial gene expression, and most sRNAs characterized today engage in direct base-pairing interactions to modulate the translation and/or stability of target mRNAs. In many cases, the ubiquitous RNA chaperone, Hfq, contributes to the establishment of RNA-RNA interactions. Although the deletion of the hfq gene is associated with a severe loss of fitness in C. crescentus, the RNA ligands of the chaperone have remained largely unexplored. Here we report on the identification of coding and non-coding transcripts associated with Hfq in C. crescentus and demonstrate Hfq-dependent post-transcriptional regulation in this organism. We show that the Hfq-bound sRNA RusT is transcriptionally controlled by the NtrYX two-component system and induced in response to iron starvation. By combining RusT pulse expression with whole-genome transcriptome analysis, we determine 16 candidate target transcripts that are deregulated, many of which encode outer membrane transporters. We hence suggest RusT to support remodeling of the C. crescentus cell surface when iron supplies are limited.IMPORTANCEThe conserved RNA-binding protein Hfq contributes significantly to the adaptation of bacteria to different environmental conditions. Hfq not only stabilizes associated sRNAs but also promotes inter-molecular base-pairing interactions with target transcripts. Hfq plays a pivotal role for growth and survival, controlling central metabolism and cell wall synthesis in the oligotroph Caulobacter crescentus. However, direct evidence for Hfq-dependent post-transcriptional regulation and potential oligotrophy in C. crescentus has been lacking. Here, we identified sRNAs and mRNAs associated with Hfq in vivo, and demonstrated the requirement of Hfq for sRNA-mediated regulation, particularly of outer membrane transporters in C. crescentus.
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Affiliation(s)
- Laura N. Vogt
- Institute of Microbiology, Faculty of Biological Sciences, Friedrich Schiller University, Jena, Germany
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Gaël Panis
- Department of Microbiology and Molecular Medicine, Faculty of Medicine/Centre Médical Universitaire, University of Geneva, Geneva, Switzerland
| | - Anna Schäpers
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Nikolai Peschek
- Institute of Microbiology, Faculty of Biological Sciences, Friedrich Schiller University, Jena, Germany
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Michaela Huber
- Institute of Microbiology, Faculty of Biological Sciences, Friedrich Schiller University, Jena, Germany
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Kai Papenfort
- Institute of Microbiology, Faculty of Biological Sciences, Friedrich Schiller University, Jena, Germany
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
- Cluster of Excellence Balance of the Microverse, Friedrich Schiller University, Jena, Germany
| | - Patrick H. Viollier
- Department of Microbiology and Molecular Medicine, Faculty of Medicine/Centre Médical Universitaire, University of Geneva, Geneva, Switzerland
| | - Kathrin S. Fröhlich
- Institute of Microbiology, Faculty of Biological Sciences, Friedrich Schiller University, Jena, Germany
- Department of Biology I, Microbiology, Ludwig-Maximilians-University Munich, Munich, Germany
- Cluster of Excellence Balance of the Microverse, Friedrich Schiller University, Jena, Germany
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3
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Yu F, Wang Z, Zhang Z, Zhou J, Li J, Chen J, Du G, Zhao X. Biosynthesis, acquisition, regulation, and upcycling of heme: recent advances. Crit Rev Biotechnol 2024:1-17. [PMID: 38228501 DOI: 10.1080/07388551.2023.2291339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 11/25/2023] [Indexed: 01/18/2024]
Abstract
Heme, an iron-containing tetrapyrrole in hemoproteins, including: hemoglobin, myoglobin, catalase, cytochrome c, and cytochrome P450, plays critical physiological roles in different organisms. Heme-derived chemicals, such as biliverdin, bilirubin, and phycocyanobilin, are known for their antioxidant and anti-inflammatory properties and have shown great potential in fighting viruses and diseases. Therefore, more and more attention has been paid to the biosynthesis of hemoproteins and heme derivatives, which depends on the adequate heme supply in various microbial cell factories. The enhancement of endogenous biosynthesis and exogenous uptake can improve the intracellular heme supply, but the excess free heme is toxic to the cells. Therefore, based on the heme-responsive regulators, several sensitive biosensors were developed to fine-tune the intracellular levels of heme. In this review, recent advances in the: biosynthesis, acquisition, regulation, and upcycling of heme were summarized to provide a solid foundation for the efficient production and application of high-value-added hemoproteins and heme derivatives.
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Affiliation(s)
- Fei Yu
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Ziwei Wang
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Zihan Zhang
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Jingwen Zhou
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Jianghua Li
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Jian Chen
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
| | - Guocheng Du
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China
| | - Xinrui Zhao
- Science Center for Future Foods, Jiangnan University, Wuxi, China
- Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China
- Jiangsu Province Engineering Research Center of Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
- Engineering Research Center of Ministry of Education on Food Synthetic Biotechnology, Jiangnan University, Wuxi, China
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4
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Newton S, Klebba PME. Fluorescent Binding Protein Sensors for Detection and Quantification of Biochemicals, Metabolites, and Natural Products. Bio Protoc 2022; 12:e4543. [PMID: 36532683 PMCID: PMC9724013 DOI: 10.21769/bioprotoc.4543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 08/29/2022] [Accepted: 09/13/2022] [Indexed: 11/06/2022] Open
Abstract
Membrane transporters and soluble binding proteins recognize particular nutrients, metabolites, vitamins, or ligands. By modifying genetically engineered single cysteine residues near the active sites of such proteins with extrinsic maleimide fluorophores,the approaches that we report create sensitive fluorescent sensors that detect, quantify, and monitor molecules that are relevant to the biochemistry, physiology, microbiology, and clinical properties of pro- and eukaryotic organisms. This protocol was validated in: J Biol Chem (2022), DOI: 10.1016/j.jbc.2022.101651 Graphical abstract.
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Affiliation(s)
- Salete Newton
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA
| | - Phillip M. E. Klebba
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA
,
*For correspondence:
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5
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Fang L, Li Y, Li Y, Cao Y, Song H. Transcriptome Analysis to Identify Crucial Genes for Reinforcing Flavins-Mediated Extracellular Electron Transfer in Shewanella oneidensis. Front Microbiol 2022; 13:852527. [PMID: 35722328 PMCID: PMC9198578 DOI: 10.3389/fmicb.2022.852527] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 05/10/2022] [Indexed: 11/13/2022] Open
Abstract
Flavins serve as the electron mediators in Shewanella oneidensis, determining the extracellular electron transfer (EET) rate. Currently, metabolic engineering of flavins biosynthetic pathway has been studied for improving EET. However, the cellular response triggered by flavins that contribute to EET remains to be elucidated. In this study, the riboflavin-overproducing strain C5 (expressing the flavins synthetic genes in plasmid PYYDT) and the PYYDT strain (harboring the empty plasmid PYYDT) in the microbial fuel cells are applied for comparative transcriptomic analyses to investigate beneficial gene targets that could improve EET. From the differentially expressed genes, we select the significantly upregulated and downregulated genes for inverse engineering in S. oneidensis. The results show that overexpression of ahpC and ccpA, and inactivation of pubA, putB, and tonB are able to improve the EET capability. Combinatorial modulation of these five genes results in the recombinant strain CM4, achieving the maximum power density of 651.78 ± 124.60 mW/m2, 1.97 folds of the parental strain. These genes modulation is speculated to reduce the ROS damage and to promote cytochrome synthesis and heme accumulation, which coherently enhance EET. Our findings facilitate in-depth understanding of the mechanism of flavins-mediated EET and provide new insights in promoting EET of S. oneidensis for electricity generation.
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Affiliation(s)
- Lixia Fang
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
| | - Yuanyuan Li
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
| | - Yan Li
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
| | - Yingxiu Cao
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
| | - Hao Song
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, China
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6
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de Lima VM, Batista BB, da Silva Neto JF. The Regulatory Protein ChuP Connects Heme and Siderophore-Mediated Iron Acquisition Systems Required for Chromobacterium violaceum Virulence. Front Cell Infect Microbiol 2022; 12:873536. [PMID: 35646721 PMCID: PMC9131926 DOI: 10.3389/fcimb.2022.873536] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 03/30/2022] [Indexed: 11/22/2022] Open
Abstract
Chromobacterium violaceum is an environmental Gram-negative beta-proteobacterium that causes systemic infections in humans. C. violaceum uses siderophore-based iron acquisition systems to overcome the host-imposed iron limitation, but its capacity to use other iron sources is unknown. In this work, we characterized ChuPRSTUV as a heme utilization system employed by C. violaceum to explore an important iron reservoir in mammalian hosts, free heme and hemoproteins. We demonstrate that the chuPRSTUV genes comprise a Fur-repressed operon that is expressed under iron limitation. The chu operon potentially encodes a small regulatory protein (ChuP), an outer membrane TonB-dependent receptor (ChuR), a heme degradation enzyme (ChuS), and an inner membrane ABC transporter (ChuTUV). Our nutrition growth experiments using C. violaceum chu deletion mutants revealed that, with the exception of chuS, all genes of the chu operon are required for heme and hemoglobin utilization in C. violaceum. The mutant strains without chuP displayed increased siderophore halos on CAS plate assays. Significantly, we demonstrate that ChuP connects heme and siderophore utilization by acting as a positive regulator of chuR and vbuA, which encode the TonB-dependent receptors for the uptake of heme (ChuR) and the siderophore viobactin (VbuA). Our data favor a model of ChuP as a heme-binding post-transcriptional regulator. Moreover, our virulence data in a mice model of acute infection demonstrate that C. violaceum uses both heme and siderophore for iron acquisition during infection, with a preference for siderophores over the Chu heme utilization system.
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7
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Kumar A, Yang T, Chakravorty S, Majumdar A, Nairn BL, Six DA, Marcondes Dos Santos N, Price SL, Lawrenz MB, Actis LA, Marques M, Russo TA, Newton SM, Klebba PE. Fluorescent sensors of siderophores produced by bacterial pathogens. J Biol Chem 2022; 298:101651. [PMID: 35101443 PMCID: PMC8921320 DOI: 10.1016/j.jbc.2022.101651] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 11/25/2022] Open
Abstract
Siderophores are iron-chelating molecules that solubilize Fe3+ for microbial utilization and facilitate colonization or infection of eukaryotes by liberating host iron for bacterial uptake. By fluorescently labeling membrane receptors and binding proteins, we created 20 sensors that detect, discriminate, and quantify apo- and ferric siderophores. The sensor proteins originated from TonB-dependent ligand-gated porins (LGPs) of Escherichia coli (Fiu, FepA, Cir, FhuA, IutA, BtuB), Klebsiella pneumoniae (IroN, FepA, FyuA), Acinetobacter baumannii (PiuA, FepA, PirA, BauA), Pseudomonas aeruginosa (FepA, FpvA), and Caulobacter crescentus (HutA) from a periplasmic E. coli binding protein (FepB) and from a human serum binding protein (siderocalin). They detected ferric catecholates (enterobactin, degraded enterobactin, glucosylated enterobactin, dihydroxybenzoate, dihydroxybenzoyl serine, cefidericol, MB-1), ferric hydroxamates (ferrichromes, aerobactin), mixed iron complexes (yersiniabactin, acinetobactin, pyoverdine), and porphyrins (hemin, vitamin B12). The sensors defined the specificities and corresponding affinities of the LGPs and binding proteins and monitored ferric siderophore and porphyrin transport by microbial pathogens. We also quantified, for the first time, broad recognition of diverse ferric complexes by some LGPs, as well as monospecificity for a single metal chelate by others. In addition to their primary ferric siderophore ligands, most LGPs bound the corresponding aposiderophore with ∼100-fold lower affinity. These sensors provide insights into ferric siderophore biosynthesis and uptake pathways in free-living, commensal, and pathogenic Gram-negative bacteria.
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Affiliation(s)
- Ashish Kumar
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Taihao Yang
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Somnath Chakravorty
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA; Department of Medicine, Jacobs School of Medicine & Biomedical Sciences, University of Buffalo School of Medicine, Buffalo, New York, USA
| | - Aritri Majumdar
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Brittany L Nairn
- Department of Biological Sciences, Bethel University, St. Paul, Minnesota, USA
| | - David A Six
- Department of Biology, Venatorx Pharmaceuticals, Inc, Malvern, Pennsylvania, USA
| | - Naara Marcondes Dos Santos
- Departamento de Microbiologia, Instituto de Ciencias Biomedicas, Universidade de São Paulo, São Paulo, Brazil
| | - Sarah L Price
- Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, Kentucky, USA
| | - Matthew B Lawrenz
- Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, Kentucky, USA
| | - Luis A Actis
- Department of Microbiology, Miami University, Oxford, Ohio, USA
| | - Marilis Marques
- Departamento de Microbiologia, Instituto de Ciencias Biomedicas, Universidade de São Paulo, São Paulo, Brazil
| | - Thomas A Russo
- Department of Medicine, Jacobs School of Medicine & Biomedical Sciences, University of Buffalo School of Medicine, Buffalo, New York, USA
| | - Salete M Newton
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA
| | - Phillip E Klebba
- Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, Kansas, USA.
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8
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Maertens L, Cherry P, Tilquin F, Van Houdt R, Matroule JY. Environmental Conditions Modulate the Transcriptomic Response of Both Caulobacter crescentus Morphotypes to Cu Stress. Microorganisms 2021; 9:1116. [PMID: 34064119 PMCID: PMC8224329 DOI: 10.3390/microorganisms9061116] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 05/18/2021] [Accepted: 05/19/2021] [Indexed: 12/13/2022] Open
Abstract
Bacteria encounter elevated copper (Cu) concentrations in multiple environments, varying from mining wastes to antimicrobial applications of copper. As the role of the environment in the bacterial response to Cu ion exposure remains elusive, we used a tagRNA-seq approach to elucidate the disparate responses of two morphotypes of Caulobacter crescentus NA1000 to moderate Cu stress in a complex rich (PYE) medium and a defined poor (M2G) medium. The transcriptome was more responsive in M2G, where we observed an extensive oxidative stress response and reconfiguration of the proteome, as well as the induction of metal resistance clusters. In PYE, little evidence was found for an oxidative stress response, but several transport systems were differentially expressed, and an increased need for histidine was apparent. These results show that the Cu stress response is strongly dependent on the cellular environment. In addition, induction of the extracytoplasmic function sigma factor SigF and its regulon was shared by the Cu stress responses in both media, and its central role was confirmed by the phenotypic screening of a sigF::Tn5 mutant. In both media, stalked cells were more responsive to Cu stress than swarmer cells, and a stronger basal expression of several cell protection systems was noted, indicating that the swarmer cell is inherently more Cu resistant. Our approach also allowed for detecting several new transcription start sites, putatively indicating small regulatory RNAs, and additional levels of Cu-responsive regulation.
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Affiliation(s)
- Laurens Maertens
- Microbiology Unit, Interdisciplinary Biosciences, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium; (L.M.); (R.V.H.)
- Research Unit in Microorganisms Biology (URBM), Narilis Institute, University of Namur, 5000 Namur, Belgium; (P.C.); (F.T.)
| | - Pauline Cherry
- Research Unit in Microorganisms Biology (URBM), Narilis Institute, University of Namur, 5000 Namur, Belgium; (P.C.); (F.T.)
| | - Françoise Tilquin
- Research Unit in Microorganisms Biology (URBM), Narilis Institute, University of Namur, 5000 Namur, Belgium; (P.C.); (F.T.)
| | - Rob Van Houdt
- Microbiology Unit, Interdisciplinary Biosciences, Belgian Nuclear Research Centre (SCK CEN), 2400 Mol, Belgium; (L.M.); (R.V.H.)
| | - Jean-Yves Matroule
- Research Unit in Microorganisms Biology (URBM), Narilis Institute, University of Namur, 5000 Namur, Belgium; (P.C.); (F.T.)
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9
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Klebba PE, Newton SMC, Six DA, Kumar A, Yang T, Nairn BL, Munger C, Chakravorty S. Iron Acquisition Systems of Gram-negative Bacterial Pathogens Define TonB-Dependent Pathways to Novel Antibiotics. Chem Rev 2021; 121:5193-5239. [PMID: 33724814 PMCID: PMC8687107 DOI: 10.1021/acs.chemrev.0c01005] [Citation(s) in RCA: 58] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Iron is an indispensable metabolic cofactor in both pro- and eukaryotes, which engenders a natural competition for the metal between bacterial pathogens and their human or animal hosts. Bacteria secrete siderophores that extract Fe3+ from tissues, fluids, cells, and proteins; the ligand gated porins of the Gram-negative bacterial outer membrane actively acquire the resulting ferric siderophores, as well as other iron-containing molecules like heme. Conversely, eukaryotic hosts combat bacterial iron scavenging by sequestering Fe3+ in binding proteins and ferritin. The variety of iron uptake systems in Gram-negative bacterial pathogens illustrates a range of chemical and biochemical mechanisms that facilitate microbial pathogenesis. This document attempts to summarize and understand these processes, to guide discovery of immunological or chemical interventions that may thwart infectious disease.
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Affiliation(s)
- Phillip E Klebba
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Salete M C Newton
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - David A Six
- Venatorx Pharmaceuticals, Inc., 30 Spring Mill Drive, Malvern, Pennsylvania 19355, United States
| | - Ashish Kumar
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Taihao Yang
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Brittany L Nairn
- Department of Biological Sciences, Bethel University, 3900 Bethel Drive, St. Paul, Minnesota 55112, United States
| | - Colton Munger
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Somnath Chakravorty
- Jacobs School of Medicine and Biomedical Sciences, SUNY Buffalo, Buffalo, New York 14203, United States
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10
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Madej M, White JBR, Nowakowska Z, Rawson S, Scavenius C, Enghild JJ, Bereta GP, Pothula K, Kleinekathoefer U, Baslé A, Ranson NA, Potempa J, van den Berg B. Structural and functional insights into oligopeptide acquisition by the RagAB transporter from Porphyromonas gingivalis. Nat Microbiol 2020; 5:1016-1025. [PMID: 32393857 PMCID: PMC7610489 DOI: 10.1038/s41564-020-0716-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 03/31/2020] [Indexed: 12/30/2022]
Abstract
Porphyromonas gingivalis, an asaccharolytic member of the Bacteroidetes, is a keystone pathogen in human periodontitis that may also contribute to the development of other chronic inflammatory diseases. P. gingivalis utilizes protease-generated peptides derived from extracellular proteins for growth, but how these peptides enter the cell is not clear. Here, we identify RagAB as the outer-membrane importer for these peptides. X-ray crystal structures show that the transporter forms a dimeric RagA2B2 complex, with the RagB substrate-binding surface-anchored lipoprotein forming a closed lid on the RagA TonB-dependent transporter. Cryo-electron microscopy structures reveal the opening of the RagB lid and thus provide direct evidence for a 'pedal bin' mechanism of nutrient uptake. Together with mutagenesis, peptide-binding studies and RagAB peptidomics, our work identifies RagAB as a dynamic, selective outer-membrane oligopeptide-acquisition machine that is essential for the efficient utilization of proteinaceous nutrients by P. gingivalis.
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Affiliation(s)
- Mariusz Madej
- Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
- Malopolska Centre of Biotechnology, Jagiellonian University, Krakow, Poland
| | - Joshua B R White
- Astbury Centre for Structural Molecular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
- The Harvard Cryo-Electron Microscopy Center for Structural Biology, Harvard Medical School, Boston, MA, USA
| | - Zuzanna Nowakowska
- Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
| | - Shaun Rawson
- Astbury Centre for Structural Molecular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
- The Harvard Cryo-Electron Microscopy Center for Structural Biology, Harvard Medical School, Boston, MA, USA
| | - Carsten Scavenius
- Interdisciplinary Nanoscience Center (iNANO) and the Department of Molecular Biology, Aarhus University, Aarhus, Denmark
| | - Jan J Enghild
- Interdisciplinary Nanoscience Center (iNANO) and the Department of Molecular Biology, Aarhus University, Aarhus, Denmark
| | - Grzegorz P Bereta
- Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
| | - Karunakar Pothula
- Department of Physics and Earth Sciences, Jacobs University Bremen, Bremen, Germany
| | | | - Arnaud Baslé
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Neil A Ranson
- Astbury Centre for Structural Molecular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK.
| | - Jan Potempa
- Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
- Department of Oral Immunology and Infectious Diseases, University of Louisville School of Dentistry, Louisville, KY, USA.
| | - Bert van den Berg
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK.
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11
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Iron acquisition system of Sphingobium sp. strain SYK-6, a degrader of lignin-derived aromatic compounds. Sci Rep 2020; 10:12177. [PMID: 32699224 PMCID: PMC7376174 DOI: 10.1038/s41598-020-68984-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 07/03/2020] [Indexed: 11/23/2022] Open
Abstract
Iron, an essential element for all organisms, acts as a cofactor of enzymes in bacterial degradation of recalcitrant aromatic compounds. The bacterial family, Sphingomonadaceae comprises various degraders of recalcitrant aromatic compounds; however, little is known about their iron acquisition system. Here, we investigated the iron acquisition system in a model bacterium capable of degrading lignin-derived aromatics, Sphingobium sp. strain SYK-6. Analyses of SYK-6 mutants revealed that FiuA (SLG_34550), a TonB-dependent receptor (TBDR), was the major outer membrane iron transporter. Three other TBDRs encoded by SLG_04340, SLG_04380, and SLG_10860 also participated in iron uptake, and tonB2 (SLG_34540), one of the six tonB comprising the Ton complex which enables TBDR-mediated transport was critical for iron uptake. The ferrous iron transporter FeoB (SLG_36840) played an important role in iron uptake across the inner membrane. The promoter activities of most of the iron uptake genes were induced under iron-limited conditions, and their regulation is controlled by SLG_29410 encoding the ferric uptake regulator, Fur. Although feoB, among all the iron uptake genes identified is highly conserved in Sphingomonad strains, the outer membrane transporters seem to be diversified. Elucidation of the iron acquisition system promises better understanding of the bacterial degradation mechanisms of aromatic compounds.
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12
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Production and Uptake of Distinct Endogenous Catecholate-Type Siderophores Are Required for Iron Acquisition and Virulence in Chromobacterium violaceum. Infect Immun 2019; 87:IAI.00577-19. [PMID: 31570563 DOI: 10.1128/iai.00577-19] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Accepted: 09/25/2019] [Indexed: 12/25/2022] Open
Abstract
Bacteria use siderophores to scavenge iron from environmental or host sources. The iron acquisition systems of Chromobacterium violaceum, a ubiquitous environmental bacterium that can cause infections in humans, are still unknown. In this work, we demonstrated that C. violaceum produces putative distinct endogenous siderophores, here named chromobactin and viobactin, and showed that they are each required for iron uptake and virulence. An in silico analysis in the genome of C. violaceum revealed that genes related to synthesis and uptake of chromobactin (cba) and viobactin (vba) are located within two secondary-metabolite biosynthetic gene clusters. Using a combination of gene deletions and siderophore detection assays, we revealed that chromobactin and viobactin are catecholate siderophores synthesized from the common precursor 2,3-dihydroxybenzoate (2,3-DHB) on two nonribosomal peptide synthetase (NRPS) enzymes (CbaF and VbaF) and taken up by two TonB-dependent receptors (CbuA and VbuA). Infection assays in mice revealed that both the synthesis and the uptake of chromobactin or viobactin are required for the virulence of C. violaceum, since only the mutant strains that do not produce any siderophores or are unable to take up both of them were attenuated for virulence. In addition, the mutant strain unable to take up both siderophores showed a pronounced attenuation of virulence in vivo and reduced neutrophil extracellular trap (NET) formation in in vitro assays, suggesting that extracellularly accumulated siderophores modulate the host immune response. Overall, our results revealed that C. violaceum uses distinct endogenous siderophores for iron uptake and its establishment in the host.
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13
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Richard KL, Kelley BR, Johnson JG. Heme Uptake and Utilization by Gram-Negative Bacterial Pathogens. Front Cell Infect Microbiol 2019; 9:81. [PMID: 30984629 PMCID: PMC6449446 DOI: 10.3389/fcimb.2019.00081] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 03/08/2019] [Indexed: 02/06/2023] Open
Abstract
Iron is a transition metal utilized by nearly all forms of life for essential cellular processes, such as DNA synthesis and cellular respiration. During infection by bacterial pathogens, the host utilizes various strategies to sequester iron in a process termed, nutritional immunity. To circumvent these defenses, Gram-negative pathogens have evolved numerous mechanisms to obtain iron from heme. In this review we outline the systems that exist in several Gram-negative pathogens that are associated with heme transport and utilization, beginning with hemolysis and concluding with heme degradation. In addition, Gram-negative pathogens must also closely regulate the intracellular concentrations of iron and heme, since high levels of iron can lead to the generation of toxic reactive oxygen species. As such, we also provide several examples of regulatory pathways that control heme utilization, showing that co-regulation with other cellular processes is complex and often not completely understood.
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Affiliation(s)
- Kaylie L Richard
- Department of Microbiology, University of Tennessee, Knoxville, TN, United States
| | - Brittni R Kelley
- Department of Microbiology, University of Tennessee, Knoxville, TN, United States
| | - Jeremiah G Johnson
- Department of Microbiology, University of Tennessee, Knoxville, TN, United States
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14
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Menikpurage IP, Barraza D, Meléndez AB, Strebe S, Mera PE. The B12 receptor BtuB alters the membrane integrity of Caulobacter crescentus. MICROBIOLOGY-SGM 2019; 165:311-323. [PMID: 30628887 DOI: 10.1099/mic.0.000753] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Vitamin B12 is one of the most complex biomolecules in nature. Since few organisms can synthesize B12de novo, most bacteria utilize highly sensitive and specialized transporters to scavenge B12 and its precursors. In Gram-negative bacteria, BtuB is the outer membrane TonB-dependent receptor for B12. In the fresh water bacterium Caulobacter crescentus, btuB is among the most highly expressed genes. In this study, we characterized the function of BtuB in C. crescentus and unveiled a potential new function of this receptor involved in cellular fitness. Under standard minimal or rich growth conditions, we found that supplements of vitamin B12 to cultures of C. crescentus provided no significant advantage in growth rate. Using a B12 methionine auxotroph, we showed that BtuB in C. crescentus is capable of transporting B12 at low pico-molar range. A btuB knockout strain displayed higher sensitivity to detergents and to changes in osmotic pressure compared to the wild-type. Electron micrographs of this knockout strain revealed a morphology defect. The sensitivity observed in the btuB knockout strain was not due to changes in membrane permeability or altered S-layer levels. Our results demonstrate that btuB deletion mutants exhibit increased susceptibility to membrane stressors, suggesting a potential role of this receptor in membrane homeostasis. Because we only tested BtuB's function under laboratory conditions, we cannot eliminate the possibility that BtuB also plays a key role as a B12 scavenger in C. crescentus when growing in its highly variable and nutrient-limited natural environment.
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Affiliation(s)
- Inoka P Menikpurage
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, USA
| | - Daniela Barraza
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, USA
| | - Ady B Meléndez
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, USA
| | - Sierra Strebe
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, USA
| | - Paola E Mera
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, USA
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15
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Leaden L, Silva LG, Ribeiro RA, Dos Santos NM, Lorenzetti APR, Alegria TGP, Schulz ML, Medeiros MHG, Koide T, Marques MV. Iron Deficiency Generates Oxidative Stress and Activation of the SOS Response in Caulobacter crescentus. Front Microbiol 2018; 9:2014. [PMID: 30210482 PMCID: PMC6120978 DOI: 10.3389/fmicb.2018.02014] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Accepted: 08/09/2018] [Indexed: 01/18/2023] Open
Abstract
In C. crescentus, iron metabolism is mainly controlled by the transcription factor Fur (ferric uptake regulator). Iron-bound Fur represses genes related to iron uptake and can directly activate the expression of genes for iron-containing proteins. In this work, we used total RNA sequencing (RNA-seq) of wild type C. crescentus growing in minimal medium under iron limitation and a fur mutant strain to expand the known Fur regulon, and to identify novel iron-regulated genes. The RNA-seq of cultures treated with the iron chelator 2-2-dypiridyl (DP) allowed identifying 256 upregulated genes and 236 downregulated genes, being 176 and 204 newly identified, respectively. Sixteen transcription factors and seven sRNAs were upregulated in iron limitation, suggesting that the response to low iron triggers a complex regulatory network. Notably, lexA along with most of its target genes were upregulated, suggesting that DP treatment caused DNA damage, and the SOS DNA repair response was activated in a RecA-dependent manner, as confirmed by RT-qPCR. Fluorescence microscopy assays using an oxidation-sensitive dye showed that wild type cells in iron limitation and the fur mutant were under endogenous oxidative stress, and a direct measurement of cellular H2O2 showed that cells in iron-limited media present a higher amount of endogenous H2O2. A mutagenesis assay using the rpoB gene as a reporter showed that iron limitation led to an increase in the mutagenesis rate. These results showed that iron deficiency causes C. crescentus cells to suffer oxidative stress and to activate the SOS response, indicating an increase in DNA damage.
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Affiliation(s)
- Laura Leaden
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Larissa G Silva
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Rodolfo A Ribeiro
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Naara M Dos Santos
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Alan P R Lorenzetti
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil
| | - Thiago G P Alegria
- Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil
| | - Mariane L Schulz
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Marisa H G Medeiros
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Tie Koide
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil
| | - Marilis V Marques
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
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16
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Santos TMA, Lammers MG, Zhou M, Sparks IL, Rajendran M, Fang D, De Jesus CLY, Carneiro GFR, Cui Q, Weibel DB. Small Molecule Chelators Reveal That Iron Starvation Inhibits Late Stages of Bacterial Cytokinesis. ACS Chem Biol 2018; 13:235-246. [PMID: 29227619 DOI: 10.1021/acschembio.7b00560] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bacterial cell division requires identification of the division site, assembly of the division machinery, and constriction of the cell envelope. These processes are regulated in response to several cellular and environmental signals. Here, we use small molecule iron chelators to characterize the surprising connections between bacterial iron homeostasis and cell division. We demonstrate that iron starvation downregulates the transcription of genes encoding proteins involved in cell division, reduces protein biosynthesis, and prevents correct positioning of the division machinery at the division site. These combined events arrest the constriction of the cell during late stages of cytokinesis in a manner distinct from known mechanisms of inhibiting cell division. Overexpression of genes encoding cell division proteins or iron transporters partially suppresses the biological activity of iron chelators and restores growth and division. We propose a model demonstrating the effect of iron availability on the regulatory mechanisms coordinating division in response to the nutritional state of the cell.
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Affiliation(s)
- Thiago M. A. Santos
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Matthew G. Lammers
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Maoquan Zhou
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Ian L. Sparks
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Madhusudan Rajendran
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Dong Fang
- Department
of Chemistry, University of Wisconsin—Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Crystal L. Y. De Jesus
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Gabriel F. R. Carneiro
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
| | - Qiang Cui
- Department
of Chemistry, University of Wisconsin—Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Douglas B. Weibel
- Department
of Biochemistry, University of Wisconsin—Madison, 440 Henry Mall, Madison, Wisconsin 53706, United States
- Department
of Chemistry, University of Wisconsin—Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
- Department
of Biomedical Engineering, University of Wisconsin—Madison, 1550 Engineering Drive, Madison, Wisconsin 53706, United States
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