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Gaddy KE, Bensch EM, Cavanagh J, Milton ME. Insights into DNA-binding motifs and mechanisms of Francisella tularensis novicida two-component system response regulator proteins QseB, KdpE, and BfpR. Biochem Biophys Res Commun 2024; 722:150150. [PMID: 38805787 DOI: 10.1016/j.bbrc.2024.150150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 05/09/2024] [Accepted: 05/20/2024] [Indexed: 05/30/2024]
Abstract
Two component system bacterial response regulators are typically DNA-binding proteins which enable the genetic regulation of many adaptive bacterial behaviors. Despite structural similarity across response regulator families, there is a diverse array of DNA-binding mechanisms. Bacteria usually encode several dozen two-component system response regulators, but Francisella tularensis only encodes three. Due to their simplified response regulatory network, Francisella species are a model for studying the role of response regulator proteins in virulence. Here, we show that Francisella response regulators QseB, KdpE, and BfpR all utilize different DNA-binding mechanisms. Our evidence suggests that QseB follows a simple mechanism whereby it binds a single inverted repeat sequence with a higher affinity upon phosphorylation. This behavior is independent of whether QseB is a positive or negative regulator of the gene as demonstrated by qseB and priM promoter sequences, respectively. Similarly, KdpE binds DNA more tightly upon phosphorylation, but also exhibits a cooperative binding isotherm. While we propose a KdpE binding site, it is possible that KdpE has a complex DNA-binding mechanism potentially involving multiple copies of KdpE being recruited to a promoter region. Finally, we show that BfpR appears to bind a region of its own promoter sequence with a lower affinity upon phosphorylation. Further structural and enzymatic work will need to be performed to deconvolute the KdpE and BfpR binding mechanisms.
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Affiliation(s)
- Keegan E Gaddy
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC, USA
| | - Elody M Bensch
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC, USA
| | - John Cavanagh
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC, USA
| | - Morgan E Milton
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC, USA.
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Carpenter AM, van Hoek ML. Development of a defibrinated human blood hemolysis assay for rapid testing of hemolytic activity compared to computational prediction. J Immunol Methods 2024; 529:113670. [PMID: 38604530 DOI: 10.1016/j.jim.2024.113670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2023] [Revised: 04/04/2024] [Accepted: 04/05/2024] [Indexed: 04/13/2024]
Abstract
Cytotoxicity studies determining hemolytic properties of antimicrobial peptides or other drugs are an important step in the development of novel therapeutics for clinical use. Hemolysis is an affordable, accessible, and rapid method for initial assessment of cellular toxicity for all drugs under development. However, variability in species of red blood cells and protocols used may result in significant differences in results. AMPs generally possess higher selectivity for bacterial cells but can have toxicity against host cells at high concentrations. Knowing the hemolytic activity of the peptides we are developing contributes to our understanding of their potential toxicity. Computational approaches for predicting hemolytic activity of AMPs exist and were tested head-to-head with our experimental results. RESULTS Starting with an observation of high hemolytic activity of LL-37 peptide against human red blood cells that were collected in EDTA, we explored alternative approaches to develop a more robust, accurate and simple hemolysis assay using defibrinated human blood. We found significant differences between the sensitivity of defibrinated red blood cells and EDTA treated red blood cells. SIGNIFICANCE Accurately determining the hemolytic activity using human red blood cells will allow for a more robust calculation of the therapeutic index of our potential antimicrobial compounds, a critical measure in their pre-clinical development. CONCLUSION We introduce a standardized, more accurate protocol for assessing hemolytic activity using defibrinated human red blood cells. This approach, facilitated by the increased commercial availability of de-identified human blood and defibrination methods, offers a robust tool for evaluating toxicity of emerging drug compounds, especially AMPs.
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Affiliation(s)
- Ashley M Carpenter
- School of Systems Biology, George Mason University, Manassas, VA 20110, United States of America
| | - Monique L van Hoek
- School of Systems Biology, George Mason University, Manassas, VA 20110, United States of America; Center for Infectious Disease Research, George Mason University, Manassas, VA 20110, United States of America.
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Fontanot A, Ellinger I, Unger WWJ, Hays JP. A Comprehensive Review of Recent Research into the Effects of Antimicrobial Peptides on Biofilms-January 2020 to September 2023. Antibiotics (Basel) 2024; 13:343. [PMID: 38667019 PMCID: PMC11047476 DOI: 10.3390/antibiotics13040343] [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: 03/11/2024] [Revised: 04/03/2024] [Accepted: 04/04/2024] [Indexed: 04/29/2024] Open
Abstract
Microbial biofilm formation creates a persistent and resistant environment in which microorganisms can survive, contributing to antibiotic resistance and chronic inflammatory diseases. Increasingly, biofilms are caused by multi-drug resistant microorganisms, which, coupled with a diminishing supply of effective antibiotics, is driving the search for new antibiotic therapies. In this respect, antimicrobial peptides (AMPs) are short, hydrophobic, and amphipathic peptides that show activity against multidrug-resistant bacteria and biofilm formation. They also possess broad-spectrum activity and diverse mechanisms of action. In this comprehensive review, 150 publications (from January 2020 to September 2023) were collected and categorized using the search terms 'polypeptide antibiotic agent', 'antimicrobial peptide', and 'biofilm'. During this period, a wide range of natural and synthetic AMPs were studied, of which LL-37, polymyxin B, GH12, and Nisin were the most frequently cited. Furthermore, although many microbes were studied, Staphylococcus aureus and Pseudomonas aeruginosa were the most popular. Publications also considered AMP combinations and the potential role of AMP delivery systems in increasing the efficacy of AMPs, including nanoparticle delivery. Relatively few publications focused on AMP resistance. This comprehensive review informs and guides researchers about the latest developments in AMP research, presenting promising evidence of the role of AMPs as effective antimicrobial agents.
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Affiliation(s)
- Alessio Fontanot
- Department of Medical Microbiology & Infectious Diseases, Erasmus University Medical Centre (Erasmus MC), Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands; (A.F.); (W.W.J.U.)
- Department of Pediatrics, Laboratory of Pediatrics, Erasmus University Medical Center Rotterdam, Sophia Children’s Hospital, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
| | - Isabella Ellinger
- Institute of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Währinger Gürtel 18–20, 1090 Vienna, Austria;
| | - Wendy W. J. Unger
- Department of Medical Microbiology & Infectious Diseases, Erasmus University Medical Centre (Erasmus MC), Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands; (A.F.); (W.W.J.U.)
- Department of Pediatrics, Laboratory of Pediatrics, Erasmus University Medical Center Rotterdam, Sophia Children’s Hospital, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
| | - John P. Hays
- Department of Medical Microbiology & Infectious Diseases, Erasmus University Medical Centre (Erasmus MC), Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands; (A.F.); (W.W.J.U.)
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Degabriel M, Valeva S, Boisset S, Henry T. Pathogenicity and virulence of Francisella tularensis. Virulence 2023; 14:2274638. [PMID: 37941380 PMCID: PMC10653695 DOI: 10.1080/21505594.2023.2274638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 10/18/2023] [Indexed: 11/10/2023] Open
Abstract
Tularaemia is a zoonotic disease caused by the Gram-negative bacterium, Francisella tularensis. Depending on its entry route into the organism, F. tularensis causes different diseases, ranging from life-threatening pneumonia to less severe ulceroglandular tularaemia. Various strains with different geographical distributions exhibit different levels of virulence. F. tularensis is an intracellular bacterium that replicates primarily in the cytosol of the phagocytes. The main virulence attribute of F. tularensis is the type 6 secretion system (T6SS) and its effectors that promote escape from the phagosome. In addition, F. tularensis has evolved a peculiar envelope that allows it to escape detection by the immune system. In this review, we cover tularaemia, different Francisella strains, and their pathogenicity. We particularly emphasize the intracellular life cycle, associated virulence factors, and metabolic adaptations. Finally, we present how F. tularensis largely escapes immune detection to be one of the most infectious and lethal bacterial pathogens.
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Affiliation(s)
- Manon Degabriel
- CIRI, Centre International de Recherche en Infectiologie, Inserm U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, Univ Lyon, LYON, France
| | - Stanimira Valeva
- CIRI, Centre International de Recherche en Infectiologie, Inserm U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, Univ Lyon, LYON, France
| | - Sandrine Boisset
- CIRI, Centre International de Recherche en Infectiologie, Inserm U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, Univ Lyon, LYON, France
- Univ. Grenoble Alpes, CHU Grenoble Alpes, CNRS, CEA, UMR5075, Institut de Biologie Structurale, Grenoble, France
| | - Thomas Henry
- CIRI, Centre International de Recherche en Infectiologie, Inserm U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, Univ Lyon, LYON, France
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Alsaab FM, Dean SN, Bobde S, Ascoli GG, van Hoek ML. Computationally Designed AMPs with Antibacterial and Antibiofilm Activity against MDR Acinetobacter baumannii. Antibiotics (Basel) 2023; 12:1396. [PMID: 37760693 PMCID: PMC10525135 DOI: 10.3390/antibiotics12091396] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/28/2023] [Accepted: 08/30/2023] [Indexed: 09/29/2023] Open
Abstract
The discovery of new antimicrobials is necessary to combat multidrug-resistant (MDR) bacteria, especially those that infect wounds and form prodigious biofilms, such as Acinetobacter baumannii. Antimicrobial peptides (AMPs) are a promising class of new therapeutics against drug-resistant bacteria, including gram-negatives. Here, we utilized a computational AMP design strategy combining database filtering technology plus positional analysis to design a series of novel peptides, named HRZN, designed to be active against A. baumannii. All of the HRZN peptides we synthesized exhibited antimicrobial activity against three MDR A. baumannii strains with HRZN-15 being the most active (MIC 4 µg/mL). This peptide also inhibited and eradicated biofilm of A. baumannii strain AB5075 at 8 and 16 µg/mL, which is highly effective. HRZN-15 permeabilized and depolarized the membrane of AB5075 rapidly, as demonstrated by the killing kinetics. HRZN 13 and 14 peptides had little to no hemolysis activity against human red blood cells, whereas HRZN-15, -16, and -17 peptides demonstrated more significant hemolytic activity. HRZN-15 also demonstrated toxicity to waxworms. Further modification of HRZN-15 could result in a new peptide with an improved toxicity profile. Overall, we successfully designed a set of new AMPs that demonstrated activity against MDR A. baumannii using a computational approach.
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Affiliation(s)
- Fahad M. Alsaab
- School of Systems Biology, George Mason University, Manassas, VA 20110, USA (S.B.)
- College of Applied Medical Sciences, King Saud bin Abdulaziz University for Health Sciences, Al Ahsa 36428, Saudi Arabia
| | - Scott N. Dean
- Center for Bio/Molecular Science and Engineering, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Shravani Bobde
- School of Systems Biology, George Mason University, Manassas, VA 20110, USA (S.B.)
| | - Gabriel G. Ascoli
- Aspiring Scientist Summer Internship Program, George Mason University, Manassas, VA 20110, USA
| | - Monique L. van Hoek
- School of Systems Biology, George Mason University, Manassas, VA 20110, USA (S.B.)
- Center for Infectious Disease Research, George Mason University, Manassas, VA 20110, USA
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Schaudinn C, Rydzewski K, Meister B, Grunow R, Heuner K. Francisella tularensis subsp. holarctica wild-type is able to colonize natural aquatic ex vivo biofilms. Front Microbiol 2023; 14:1113412. [PMID: 36860486 PMCID: PMC9969146 DOI: 10.3389/fmicb.2023.1113412] [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: 12/01/2022] [Accepted: 01/16/2023] [Indexed: 02/15/2023] Open
Abstract
Biofilms are a matrix-associated lifestyle of microbial communities, often enabling survivability and persistence of such bacteria. The objective of this study was to investigate the survival of the wild-type strain A-271 of Francisella tularensis subsp. holarctica (Fth) in a natural aquatic ex vivo biofilm. To that purpose, we allowed Fth A-271 to produce its own biofilm on solid surfaces but also to colonize naturally formed biofilms from aquatic habitats, which were infected with Francisella in the laboratory. The survival rates of the bacteria in biofilms were compared to those of planktonic bacteria as a function of the employed culture condition. It could be shown by light- and electron microscopy that Fth is able to form a complex, matrix-associated biofilm. The biofilm form of Francisella showed longer cultivability on agar plates in natural water when compared to planktonic (free-living) bacteria. Be it as a part of the existing ex vivo biofilm or free-floating above as planktonic bacteria, more than 80% of Francisella were not only able to survive under these conditions for 28 days, but even managed to establish microcolonies and areas with their own exclusive biofilm architecture within the ex vivo biofilm. Here, we can demonstrate for the first time that a Francisella tularensis wild-type strain (Type B) is able to successfully colonize an aquatic multi-species ex vivo biofilm. It is worthwhile to speculate that Fth might become more persistent in the environment when it forms its own biofilm or integrates in an existing one. Multi-species biofilms have been shown to be more resistant against stress compared to single-species biofilms. This may have an important impact on the long-term survival of Francisella in aquatic habitats and infection cycles in nature.
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Affiliation(s)
- Christoph Schaudinn
- Centre for Biological Threats and Special Pathogens, Advanced Light and Electron Microscopy (ZBS 4), Robert Koch Institute, Berlin, Germany
| | - Kerstin Rydzewski
- Working Group: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany,Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
| | - Beate Meister
- Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
| | - Roland Grunow
- Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
| | - Klaus Heuner
- Working Group: Cellular Interactions of Bacterial Pathogens, Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany,Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany,*Correspondence: Klaus Heuner, ✉
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Palethorpe S, Milton ME, Pesci EC, Cavanagh J. Structure of the Acinetobacter baumannii PmrA receiver domain and insights into clinical mutants affecting DNA-binding and promoting colistin resistance. J Biochem 2021; 170:787-800. [PMID: 34585233 DOI: 10.1093/jb/mvab102] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 09/22/2021] [Indexed: 11/14/2022] Open
Abstract
Acinetobacter baumannii is an insidious emerging nosocomial pathogen that has developed resistance to all available antimicrobials, including the last resort antibiotic, colistin. Colistin resistance often occurs due to mutations in the PmrAB two component regulatory system. To better understand the regulatory mechanisms contributing to colistin resistance, we have biochemically characterized the A. baumannii PmrA response regulator. Initial DNA-binding analysis shows that A. baumannii PmrA bound to the Klebsiella pneumoniae PmrA box motif. This prompted analysis of the putative A. baumannii PmrAB regulon which indicated that the A. baumannii PmrA consensus box is 5'- HTTAAD N5 HTTAAD. Additionally, we provide the first structural information for the A. baumannii PmrA N-terminal domain through X-ray crystallography, and we present a full-length model using molecular modeling. From these studies, we were able to infer the effects of two critical PmrA mutations, PmrA::I13M and PmrA::P102R, both of which confer increased colistin resistance. Based on these data, we suggest structural and dynamic reasons for how these mutations can affect PmrA function and hence encourage resistive traits. Understanding these mechanisms will aid in the development of new targeted antimicrobial therapies.
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Affiliation(s)
- Samantha Palethorpe
- Department of Microbiology and Immunology Brody School of Medicine East Carolina University Greenville, NC 27834 United States
| | - Morgan E Milton
- Department of Biochemistry and Molecular Biology Brody School of Medicine East Carolina University Greenville, NC 27834 United States
| | - Everett C Pesci
- Department of Microbiology and Immunology Brody School of Medicine East Carolina University Greenville, NC 27834 United States
| | - John Cavanagh
- Department of Biochemistry and Molecular Biology Brody School of Medicine East Carolina University Greenville, NC 27834 United States
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Kassinger SJ, van Hoek ML. Genetic Determinants of Antibiotic Resistance in Francisella. Front Microbiol 2021; 12:644855. [PMID: 34054749 PMCID: PMC8149597 DOI: 10.3389/fmicb.2021.644855] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 03/25/2021] [Indexed: 12/21/2022] Open
Abstract
Tularemia, caused by Francisella tularensis, is endemic to the northern hemisphere. This zoonotic organism has historically been developed into a biological weapon. For this Tier 1, Category A select agent, it is important to expand our understanding of its mechanisms of antibiotic resistance (AMR). Francisella is unlike many Gram-negative organisms in that it does not have significant plasmid mobility, and does not express AMR mechanisms on plasmids; thus plasmid-mediated resistance does not occur naturally. It is possible to artificially introduce plasmids with AMR markers for cloning and gene expression purposes. In this review, we survey both the experimental research on AMR in Francisella and bioinformatic databases which contain genomic and proteomic data. We explore both the genetic determinants of intrinsic AMR and naturally acquired or engineered antimicrobial resistance as well as phenotypic resistance in Francisella. Herein we survey resistance to beta-lactams, monobactams, carbapenems, aminoglycosides, tetracycline, polymyxins, macrolides, rifampin, fosmidomycin, and fluoroquinolones. We also highlight research about the phenotypic AMR difference between planktonic and biofilm Francisella. We discuss newly developed methods of testing antibiotics against Francisella which involve the intracellular nature of Francisella infection and may better reflect the eventual clinical outcomes for new antibiotic compounds. Understanding the genetically encoded determinants of AMR in Francisella is key to optimizing the treatment of patients and potentially developing new antimicrobials for this dangerous intracellular pathogen.
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Affiliation(s)
| | - Monique L. van Hoek
- School of Systems Biology, George Mason University, Manassas, VA, United States
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Control of Francisella tularensis Virulence at Gene Level: Network of Transcription Factors. Microorganisms 2020; 8:microorganisms8101622. [PMID: 33096715 PMCID: PMC7588896 DOI: 10.3390/microorganisms8101622] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 10/14/2020] [Accepted: 10/18/2020] [Indexed: 02/07/2023] Open
Abstract
Regulation of gene transcription is the initial step in the complex process that controls gene expression within bacteria. Transcriptional control involves the joint effort of RNA polymerases and numerous other regulatory factors. Whether global or local, positive or negative, regulators play an essential role in the bacterial cell. For instance, some regulators specifically modify the transcription of virulence genes, thereby being indispensable to pathogenic bacteria. Here, we provide a comprehensive overview of important transcription factors and DNA-binding proteins described for the virulent bacterium Francisella tularensis, the causative agent of tularemia. This is an unexplored research area, and the poorly described networks of transcription factors merit additional experimental studies to help elucidate the molecular mechanisms of pathogenesis in this bacterium, and how they contribute to disease.
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