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Oliveira NFB, Ladokhin AS, Machuqueiro M. Constant-pH MD simulations of the protonation-triggered conformational switching in diphtheria toxin translocation domain. Biophys J 2024:S0006-3495(24)00589-7. [PMID: 39215463 DOI: 10.1016/j.bpj.2024.08.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2024] [Revised: 07/16/2024] [Accepted: 08/26/2024] [Indexed: 09/04/2024] Open
Abstract
Protonation of key residues in the diphtheria toxin translocation (T)-domain triggered by endosomal acidification is critical for inducing a series of conformational transitions critical for the cellular entry of the toxin. Previous experiments revealed the importance of histidine residues in modulating pH-dependent transitions. They suggested the presence of a "safety latch" preventing premature refolding of the T-domain by a yet poorly understood mechanism. Here, we used constant-pH molecular dynamics simulations to systematically investigate the protonation sequence in the wild-type T-domain and the following mutants: H223Q, H257Q, E259Q, and H223Q/H257Q. Comparison of these computational results with previous experimental data on T-domain stability and activity with the H-to-Q replacements confirms the role of H223 (pKa = 6.5) in delaying the protonation of the main trigger, H257 (pKa = 2.2 in the WT and pKa = 4.9 in H223Q). Our calculations also reveal a very low pKa for a neighboring acidic residue E259, which does not get protonated even during simulations at pH 3. This residue also contributes to the formation of the safety latch, with the pKa of H257 increasing from 2.2 to 5.1 upon E259Q replacement. In contrast, the latter replacement has virtually no effect on the protonation of the H223. Thus, we conclude that the interplay of the protonation in the H223/H257/E259 triad has evolved to prevent triggering the accidental refolding of the T-domain by a fluctuation in the protonation of the main trigger at neutral pH, before the incorporation of the toxin inside the endosome. Subsequent acidification of the endosome overcomes the safety latch and triggers conformational switching via repulsion of H223+ and H257+. This protonation/conformation relationship corroborates experimental findings and offers a detailed stepwise molecular description of the transition mechanism, which can be instrumental in optimizing the potential applications of the T-domain for targeted delivery of therapies to tumors and other diseased acidic tissues.
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Affiliation(s)
- Nuno F B Oliveira
- BioISI - Instituto de Biosistemas e Ciências Integrativas, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, Kansas, USA.
| | - Miguel Machuqueiro
- BioISI - Instituto de Biosistemas e Ciências Integrativas, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal.
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Ulhuq FR, Mariano G. Bacterial pore-forming toxins. MICROBIOLOGY (READING, ENGLAND) 2022; 168:001154. [PMID: 35333704 PMCID: PMC9558359 DOI: 10.1099/mic.0.001154] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 02/03/2022] [Indexed: 12/11/2022]
Abstract
Pore-forming toxins (PFTs) are widely distributed in both Gram-negative and Gram-positive bacteria. PFTs can act as virulence factors that bacteria utilise in dissemination and host colonisation or, alternatively, they can be employed to compete with rival microbes in polymicrobial niches. PFTs transition from a soluble form to become membrane-embedded by undergoing large conformational changes. Once inserted, they perforate the membrane, causing uncontrolled efflux of ions and/or nutrients and dissipating the protonmotive force (PMF). In some instances, target cells intoxicated by PFTs display additional effects as part of the cellular response to pore formation. Significant progress has been made in the mechanistic description of pore formation for the different PFTs families, but in several cases a complete understanding of pore structure remains lacking. PFTs have evolved recognition mechanisms to bind specific receptors that define their host tropism, although this can be remarkably diverse even within the same family. Here we summarise the salient features of PFTs and highlight where additional research is necessary to fully understand the mechanism of pore formation by members of this diverse group of protein toxins.
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Affiliation(s)
- Fatima R. Ulhuq
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, UK
| | - Giuseppina Mariano
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, UK
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Shatursky OY, Manoilov KY, Gorbatiuk OB, Usenko MO, Zhukova DA, Vovk AI, Kobzar OL, Trikash IO, Borisova TA, Kolibo DV, Komisarenko SV. The geometry of diphtheria toxoid CRM197 channel assessed by thiazolium salts and nonelectrolytes. Biophys J 2021; 120:2577-2591. [PMID: 33940022 DOI: 10.1016/j.bpj.2021.04.028] [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: 11/26/2020] [Revised: 03/01/2021] [Accepted: 04/27/2021] [Indexed: 11/18/2022] Open
Abstract
The geometry of the channel formed by nontoxic derivative of diphtheria toxin CRM197 in lipid bilayer was determined using the dependence of single-channel conductance upon the hydrodynamic radii of different nonelectrolytes. It was found that the cis entrance of CRM197 channel on the side of membrane to which the toxoid was added at pH 4.8 and the trans entrance on the opposite side at pH 6.0 had effective radii of 3.90 and 3.48 Å, respectively. The 3-alkyloxycarbonylmethyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium salts reversibly reduced current via CRM197 channels. The potency of the blockers increased with increasing length of alkyl chain at symmetric pH 6.0 and remained high and stable at pH 4.8 on the cis side. Comparative analysis of CRM197 and amphotericin B pore size with the inhibitory action of thiazolium salts revealed a significant increase in CRM197 pore dimension at pH 6.0. Addition of thiazolium salt with nine carbons alkyl tail increased by ∼30% the viability of human carcinoma cells A431 treated with diphtheria toxin.
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Affiliation(s)
- Oleg Ya Shatursky
- Department of Neurochemistry, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine.
| | - Kyrylo Yu Manoilov
- Department of Molecular Immunology, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
| | - Oksana B Gorbatiuk
- Department of Cell Regulatory Mechanisms, Institute of Molecular Biology and Genetics NAS of Ukraine, Zabolotnogo Str. 150, Kyiv 03143, Ukraine; State Institute of Genetic and Regenerative Medicine, NAMS of Ukraine, Andriivsky ds. 28 A, Kyiv, Ukraine
| | - Mariya O Usenko
- Department of Cell Regulatory Mechanisms, Institute of Molecular Biology and Genetics NAS of Ukraine, Zabolotnogo Str. 150, Kyiv 03143, Ukraine; State Institute of Genetic and Regenerative Medicine, NAMS of Ukraine, Andriivsky ds. 28 A, Kyiv, Ukraine
| | - Dariia A Zhukova
- Department of Molecular Immunology, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
| | - Andriy I Vovk
- Department of Bioorganic Mechanisms, V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry, NAS of Ukraine, Murmanska Str. 1, Kyiv 02094, Ukraine
| | - Oleksandr L Kobzar
- Department of Bioorganic Mechanisms, V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry, NAS of Ukraine, Murmanska Str. 1, Kyiv 02094, Ukraine
| | - Irene O Trikash
- Department of Neurochemistry, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
| | - Tatiana A Borisova
- Department of Neurochemistry, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
| | - Denys V Kolibo
- Department of Molecular Immunology, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
| | - Serhiy V Komisarenko
- Department of Molecular Immunology, Palladin Institute of Biochemistry, NAS of Ukraine, Leontovich Str. 9, Kyiv 01054, Ukraine
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Leka O, Vallese F, Pirazzini M, Berto P, Montecucco C, Zanotti G. Diphtheria toxin conformational switching at acidic pH. FEBS J 2014; 281:2115-22. [DOI: 10.1111/febs.12783] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 03/05/2014] [Accepted: 03/11/2014] [Indexed: 01/01/2023]
Affiliation(s)
- Oneda Leka
- Department of Biomedical Sciences; University of Padua; Italy
| | | | - Marco Pirazzini
- Department of Biomedical Sciences; University of Padua; Italy
| | - Paola Berto
- Department of Biomedical Sciences; University of Padua; Italy
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Mapingire OS, Wager B, Delcour AH. Electrophysiological characterization of bacterial pore-forming proteins in planar lipid bilayers. Methods Mol Biol 2013; 966:381-396. [PMID: 23299748 DOI: 10.1007/978-1-62703-245-2_24] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Together with patch-clamp, the planar lipid bilayer technique is one of the electrophysiological approaches used to study the biophysical properties of bacterial pore-forming proteins. Electrophysiological studies have provided important insight into the mechanistic details underlying the function of this class of proteins. Although there are different apparatus designs and variations to the process of obtaining channel recordings, the general architecture of a planar lipid bilayer setup involves two compartments filled with an ionic solution and separated by a septum with a micro-aperture, where a phospholipid bilayer is formed, and an amplifier used to clamp the membrane potential and record currents. Bacterial outer membrane porins and translocons, among others, can be reconstituted in this bilayer and their electrophysiology probed in different physicochemical conditions or through functional assays with substrates or potential modulators. This chapter describes specifically the reconstitution of detergent purified outer membrane pore-forming proteins into artificial lipid membranes using a laboratory customized planar lipid bilayer apparatus and the subsequent recording of channel activity under voltage clamp.
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Affiliation(s)
- Owen S Mapingire
- Department of Biology and Biochemistry, University of Houston, Houston, TX, USA
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Jakes KS, Finkelstein A. The colicin Ia receptor, Cir, is also the translocator for colicin Ia. Mol Microbiol 2009; 75:567-78. [PMID: 19919671 DOI: 10.1111/j.1365-2958.2009.06966.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Colicin Ia, a channel-forming bactericidal protein, uses the outer membrane protein, Cir, as its primary receptor. To kill Escherichia coli, it must cross this membrane. The crystal structure of Ia receptor-binding domain bound to Cir, a 22-stranded plugged beta-barrel protein, suggests that the plug does not move. Therefore, another pathway is needed for the colicin to cross the outer membrane, but no 'second receptor' has ever been identified for TonB-dependent colicins, such as Ia. We show that if the receptor-binding domain of colicin Ia is replaced by that of colicin E3, this chimera effectively kills cells, provided they have the E3 receptor (BtuB), Cir, and TonB. This is consistent with wild-type Ia using one Cir as its primary receptor (BtuB in the chimera) and a second Cir as the translocation pathway for its N-terminal translocation (T) domain and its channel-forming C-terminal domain. Deletion of colicin Ia's receptor-binding domain results in a protein that kills E. coli, albeit less effectively, provided they have Cir and TonB. We show that purified T domain competes with Ia and protects E. coli from being killed by it. Thus, in addition to binding to colicin Ia's receptor-binding domain, Cir also binds weakly to its translocation domain.
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Affiliation(s)
- Karen S Jakes
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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Abstract
Bacterial pathogens utilize toxins to modify or kill host cells. The bacterial ADP-ribosyltransferases are a family of protein toxins that covalently transfer the ADP-ribose portion of NAD to host proteins. Each bacterial ADP-ribosyltransferase toxin modifies a specific host protein(s) that yields a unique pathology. These toxins possess the capacity to enter a host cell or to use a bacterial Type III apparatus for delivery into the host cell. Advances in our understanding of bacterial toxin action parallel the development of biophysical and structural biology as well as our understanding of the mammalian cell. Bacterial toxins have been utilized as vaccines, as tools to dissect host cell physiology, and more recently for the development of novel therapies to treat human disease.
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Affiliation(s)
- Qing Deng
- Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
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Oligomerization of membrane-bound diphtheria toxin (CRM197) facilitates a transition to the open form and deep insertion. Biophys J 2007; 94:2115-27. [PMID: 18055530 DOI: 10.1529/biophysj.107.113498] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Diphtheria toxin (DT) contains separate domains for receptor-specific binding, translocation, and enzymatic activity. After binding to cells, DT is taken up into endosome-like acidic compartments where the translocation domain inserts into the endosomal membrane and releases the catalytic domain into the cytosol. The process by which the catalytic domain is translocated across the endosomal membrane is known to involve pH-induced conformational changes; however, the molecular mechanisms are not yet understood, in large part due to the challenge of probing the conformation of the membrane-bound protein. In this work neutron reflection provided detailed conformational information for membrane-bound DT (CRM197) in situ. The data revealed that the bound toxin oligomerizes with increasing DT concentration and that the oligomeric form (and only the oligomeric form) undergoes a large extension into solution with decreasing pH that coincides with deep insertion of residues into the membrane. We interpret the large extension as a transition to the open form. These results thus indicate that as a function of bulk DT concentration, adsorbed DT passes from an inactive state with a monomeric dimension normal to the plane of the membrane to an active state with a dimeric dimension normal to the plane of the membrane.
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