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Lisboa J, Pereira C, Pinto RD, Rodrigues IS, Pereira LMG, Pinheiro B, Oliveira P, Pereira PJB, Azevedo JE, Durand D, Benz R, do Vale A, Dos Santos NMS. Unconventional structure and mechanisms for membrane interaction and translocation of the NF-κB-targeting toxin AIP56. Nat Commun 2023; 14:7431. [PMID: 37973928 PMCID: PMC10654918 DOI: 10.1038/s41467-023-43054-z] [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: 05/15/2023] [Accepted: 10/30/2023] [Indexed: 11/19/2023] Open
Abstract
Bacterial AB toxins are secreted key virulence factors that are internalized by target cells through receptor-mediated endocytosis, translocating their enzymatic domain to the cytosol from endosomes (short-trip) or the endoplasmic reticulum (long-trip). To accomplish this, bacterial AB toxins evolved a multidomain structure organized into either a single polypeptide chain or non-covalently associated polypeptide chains. The prototypical short-trip single-chain toxin is characterized by a receptor-binding domain that confers cellular specificity and a translocation domain responsible for pore formation whereby the catalytic domain translocates to the cytosol in an endosomal acidification-dependent way. In this work, the determination of the three-dimensional structure of AIP56 shows that, instead of a two-domain organization suggested by previous studies, AIP56 has three-domains: a non-LEE encoded effector C (NleC)-like catalytic domain associated with a small middle domain that contains the linker-peptide, followed by the receptor-binding domain. In contrast to prototypical single-chain AB toxins, AIP56 does not comprise a typical structurally complex translocation domain; instead, the elements involved in translocation are scattered across its domains. Thus, the catalytic domain contains a helical hairpin that serves as a molecular switch for triggering the conformational changes necessary for membrane insertion only upon endosomal acidification, whereas the middle and receptor-binding domains are required for pore formation.
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Affiliation(s)
- Johnny Lisboa
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal.
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal.
| | - Cassilda Pereira
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
| | - Rute D Pinto
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
| | - Inês S Rodrigues
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
| | - Liliana M G Pereira
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
| | - Bruno Pinheiro
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
- Doctoral Program in Molecular and Cell Biology (MCbiology), Instituto de Ciências Biomédicas Abel Salazar - Universidade do Porto, Porto, Portugal
| | - Pedro Oliveira
- EPIUnit, ICBAS-Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
| | - Pedro José Barbosa Pereira
- Biomolecular Structure Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Macromolecular Structure Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
| | - Jorge E Azevedo
- ICBAS-Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
- Organelle Biogenesis and Function, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Organelle Biogenesis and Function, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
| | - Dominique Durand
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Roland Benz
- Science Faculty, Constructor University, Bremen, Germany
| | - Ana do Vale
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal
| | - Nuno M S Dos Santos
- Fish Immunology and Vaccinology Group, IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, 4200-135, Porto, Portugal.
- Fish Immunology and Vaccinology Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135, Porto, Portugal.
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Chen W, Ruan M, Zou M, Liu F, Liu H. Clinical Significance of Non-Coding RNA Regulation of Programmed Cell Death in Hepatocellular Carcinoma. Cancers (Basel) 2023; 15:4187. [PMID: 37627215 PMCID: PMC10452865 DOI: 10.3390/cancers15164187] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Revised: 08/02/2023] [Accepted: 08/11/2023] [Indexed: 08/27/2023] Open
Abstract
Hepatocellular carcinoma (HCC) is a widely prevalent and malignantly progressive tumor. Most patients are typically diagnosed with HCC at an advanced stage, posing significant challenges in the execution of curative surgical interventions. Non-coding RNAs (ncRNAs) represent a distinct category of RNA molecules not directly involved in protein synthesis. However, they possess the remarkable ability to regulate gene expression, thereby exerting significant regulatory control over cellular processes. Notably, ncRNAs have been implicated in the modulation of programmed cell death (PCD), a crucial mechanism that various therapeutic agents target in the fight against HCC. This review summarizes the clinical significance of ncRNA regulation of PCD in HCC, including patient diagnosis, prognosis, drug resistance, and side effects. The aim of this study is to provide new insights and directions for the diagnosis and drug treatment strategies of HCC.
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Affiliation(s)
| | | | | | - Fuchen Liu
- The Third Department of Hepatic Surgery, Eastern Hepatobiliary Surgery Hospital, Naval Medical University, Shanghai 200438, China; (W.C.); (M.R.)
| | - Hui Liu
- The Third Department of Hepatic Surgery, Eastern Hepatobiliary Surgery Hospital, Naval Medical University, Shanghai 200438, China; (W.C.); (M.R.)
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Rodnin MV, Vasques-Montes V, Kyrychenko A, Oliveira NFB, Kashipathy MM, Battaile KP, Douglas J, Lovell S, Machuqueiro M, Ladokhin AS. Histidine Protonation and Conformational Switching in Diphtheria Toxin Translocation Domain. Toxins (Basel) 2023; 15:410. [PMID: 37505680 PMCID: PMC10467104 DOI: 10.3390/toxins15070410] [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: 05/10/2023] [Revised: 06/06/2023] [Accepted: 06/21/2023] [Indexed: 07/29/2023] Open
Abstract
Protonation of key histidine residues has been long implicated in the acid-mediated cellular action of the diphtheria toxin translocation (T-) domain, responsible for the delivery of the catalytic domain into the cell. Here, we use a combination of computational (constant-pH Molecular Dynamics simulations) and experimental (NMR, circular dichroism, and fluorescence spectroscopy along with the X-ray crystallography) approaches to characterize the initial stages of conformational change happening in solution in the wild-type T-domain and in the H223Q/H257Q double mutant. This replacement suppresses the acid-induced transition, resulting in the retention of a more stable protein structure in solutions at pH 5.5 and, consequently, in reduced membrane-disrupting activity. Here, for the first time, we report the pKa values of the histidine residues of the T-domain, measured by NMR-monitored pH titrations. Most peaks in the histidine side chain spectral region are titrated with pKas ranging from 6.2 to 6.8. However, the two most up-field peaks display little change down to pH 6, which is a limiting pH for this protein in solution at concentrations required for NMR. These peaks are absent in the double mutant, suggesting they belong to H223 and H257. The constant-pH simulations indicate that for the T-domain in solution, the pKa values for histidine residues range from 3.0 to 6.5, with those most difficult to protonate being H251 and H257. Taken together, our experimental and computational data demonstrate that previously suggested cooperative protonation of all six histidines in the T-domain does not occur.
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Affiliation(s)
- Mykola V. Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
| | - Victor Vasques-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
| | - Alexander Kyrychenko
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, 61022 Kharkiv, Ukraine
| | - Nuno F. B. Oliveira
- Institute of Biosystems and Integrative Sciences, University of Lisbon, 1749-016 Lisbon, Portugal (M.M.)
| | - Maithri M. Kashipathy
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66047, USA (S.L.)
| | | | - Justin Douglas
- COBRE Bio-NMR Laboratory, University of Kansas, Lawrence, KS 66045, USA;
| | - Scott Lovell
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, Lawrence, KS 66047, USA (S.L.)
| | - Miguel Machuqueiro
- Institute of Biosystems and Integrative Sciences, University of Lisbon, 1749-016 Lisbon, Portugal (M.M.)
| | - Alexey S. Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas School of Medicine, Kansas City, KS 66160, USA (A.K.)
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Membrane Interactions of Apoptotic Inhibitor Bcl-xL: What Can Be Learned using Fluorescence Spectroscopy. BBA ADVANCES 2023; 3:100076. [PMID: 37082264 PMCID: PMC10074936 DOI: 10.1016/j.bbadva.2023.100076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 01/12/2023] [Accepted: 01/12/2023] [Indexed: 01/15/2023] Open
Abstract
Permeabilization of the mitochondrial outer membrane-a point of no return in apoptotic regulation-is tightly controlled by proteins of the Bcl-2 family. Apoptotic inhibitor Bcl-xL is an important member of this family, responsible for blocking the permeabilization, and is also a promising target for anti-cancer drugs. Bcl-xL exists in the following conformations, each believed to play a role in the inhibition of apoptosis: (i) a soluble folded conformation, (ii) a membrane-anchored (by its C-terminal α8 helix) form, which retains the same fold as in solution and (iii) refolded membrane-inserted conformations, for which no structural data are available. In this review, we present the summary of the application of various methods of fluorescence spectroscopy for studying membrane interaction of Bcl-xL, and specifically the formation of the refolded inserted conformation. We discuss the application of environment-sensitive probes, Förster resonance energy transfer, fluorescence correlation spectroscopy, and fluorescent quenching for structural, thermodynamic, and functional characterization of protein-lipid interactions, which can benefit studies of other members of Bcl-2 (e.g., Bax, BAK, Bid). The conformational switching between various conformations of Bcl-xL depends on the presence of divalent cations, pH and lipid composition. This insertion-refolding transition also results in the release of the BH4 regulatory domain from the folded structure of Bcl-xL, which is relevant to the lipid-regulated conversion between canonical and non-canonical modes of apoptotic inhibition.
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Structures of distant diphtheria toxin homologs reveal functional determinants of an evolutionarily conserved toxin scaffold. Commun Biol 2022; 5:375. [PMID: 35440624 PMCID: PMC9018708 DOI: 10.1038/s42003-022-03333-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 03/30/2022] [Indexed: 01/29/2023] Open
Abstract
Diphtheria toxin (DT) is the archetype for bacterial exotoxins implicated in human diseases and has played a central role in defining the field of toxinology since its discovery in 1888. Despite being one of the most extensively characterized bacterial toxins, the origins and evolutionary adaptation of DT to human hosts remain unknown. Here, we determined the first high-resolution structures of DT homologs outside of the Corynebacterium genus. DT homologs from Streptomyces albireticuli (17% identity to DT) and Seinonella peptonophila (20% identity to DT), despite showing no toxicity toward human cells, display significant structural similarities to DT sharing both the overall Y-shaped architecture of DT as well as the individual folds of each domain. Through a systematic investigation of individual domains, we show that the functional determinants of host range extend beyond an inability to bind cellular receptors; major differences in pH-induced pore-formation and cytosolic release further dictate the delivery of toxic catalytic moieties into cells, thus providing multiple mechanisms for a conserved structural fold to adapt to different hosts. Our work provides structural insights into the expanding DT family of toxins, and highlights key transitions required for host adaptation. Toxic proteins are responsible for the disease symptoms accompanying bacterial infections. Sugiman-Marangos et al. report crystal structures of two diphtheria toxin homologs, therefore providing structural insights into this family of toxins and the evolutionary adaptation of these toxins to human hosts.
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O'Neil PT, Vasquez-Montes V, Swint-Kruse L, Baldwin MR, Ladokhin AS. Spectroscopic evidence of tetanus toxin translocation domain bilayer-induced refolding and insertion. Biophys J 2021; 120:4763-4776. [PMID: 34555358 PMCID: PMC8595737 DOI: 10.1016/j.bpj.2021.09.030] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 08/03/2021] [Accepted: 09/16/2021] [Indexed: 12/21/2022] Open
Abstract
Tetanus neurotoxin (TeNT) is an A-B toxin with three functional domains: endopeptidase, translocation (HCT), and receptor binding. Endosomal acidification triggers HCT to interact with and insert into the membrane, translocating the endopeptidase across the bilayer. Although the function of HCT is well defined, the mechanism by which it accomplishes this task is unknown. To gain insight into the HCT membrane interaction on both local and global scales, we utilized an isolated, beltless HCT variant (bHCT), which retained the ability to release potassium ions from vesicles. To examine which bHCT residues interact with the membrane, we widely sampled the surface of bHCT using 47 single-cysteine variants labeled with the environmentally sensitive fluorophore NBD. At neutral pH, no interaction was observed for any variant. In contrast, all NBD-labeled positions reported environmental change in the presence of acidic pH and membranes containing anionic lipids. We then examined the conformation of inserted bHCT using circular dichroism and intrinsic fluorescence. Upon entering the membrane, bHCT retained predominantly α-helical secondary structure, whereas the tertiary structure exhibited substantial refolding. The use of lipid-attached quenchers revealed that at least one of the three tryptophan residues penetrated deep into the hydrocarbon core of the membrane, suggesting formation of a bHCT transmembrane conformation. The possible conformational topology was further explored with the hydropathy analysis webtool MPEx, which identified a large, potential α-helical transmembrane region. Altogether, the spectroscopic evidence supports a model in which, upon acidification, the majority of TeNT bHCT entered the membrane with a concurrent change in tertiary structure.
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Affiliation(s)
- Pierce T O'Neil
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas
| | - Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas
| | - Liskin Swint-Kruse
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas
| | - Michael R Baldwin
- Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas.
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Lehti TA, Pajunen MI, Jokilammi A, Korja M, Lilie H, Vettenranta K, Finne J. Design of a Cytotoxic Neuroblastoma-Targeting Agent Using an Enzyme Acting on Polysialic Acid Fused to a Toxin. Mol Cancer Ther 2021; 20:1996-2007. [PMID: 34315766 DOI: 10.1158/1535-7163.mct-20-1031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 05/26/2021] [Accepted: 07/15/2021] [Indexed: 11/16/2022]
Abstract
Polysialic acid, an abundant cell surface component of the developing nervous system, which declines rapidly postnatally to virtual absence in the majority of adult tissues, is highly expressed in some malignant tumors including neuroblastoma. We found that the binding of a noncatalytic endosialidase to polysialic acid causes internalization of the complex from the surface of neuroblastoma kSK-N-SH cells, a subline of SK-N-SH, and leads to a complete relocalization of polysialic acid to the intracellular compartment. The binding and uptake of the endosialidase is polysialic acid-dependent as it is inhibited by free excess ligand or removal of polysialic acid by active endosialidase, and does not happen if catalytic endosialidase is used in place of inactive endosialidase. A fusion protein composed of the noncatalytic endosialidase and the cytotoxic portion of diphtheria toxin was prepared to investigate whether the cellular uptake observed could be used for the specific elimination of polysialic acid-containing cells. The conjugate toxin was found to be toxic to polysialic acid-positive kSK-N-SH with an IC50 of 1.0 nmol/L. Replacing the noncatalytic endosialidase with active endosialidase decreased the activity to the level of nonconjugated toxin. Normal nonmalignant cells were selectively resistant to the toxin conjugate. The results demonstrate that noncatalytic endosialidase induces a quantitative removal and cellular uptake of polysialic acid from the cell surface which, by conjugation with diphtheria toxin fragment, can be exploited for the selective elimination of polysialic acid-containing tumor cells.
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Affiliation(s)
- Timo A Lehti
- Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
| | - Maria I Pajunen
- Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
| | - Anne Jokilammi
- Institute of Biomedicine, Cancer Laboratories and Medicity Research Laboratories, Faculty of Medicine, University of Turku, Turku, Finland
| | - Miikka Korja
- Department of Neurosurgery, Helsinki University Hospital, University of Helsinki, Helsinki, Finland
| | - Hauke Lilie
- Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Kim Vettenranta
- University of Helsinki and Hospital for Children and Adolescents, Helsinki University Central Hospital, Helsinki, Finland
| | - Jukka Finne
- Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
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Pezeshkian W, Shillcock JC, Ipsen JH. Computational Approaches to Explore Bacterial Toxin Entry into the Host Cell. Toxins (Basel) 2021; 13:toxins13070449. [PMID: 34203472 PMCID: PMC8309782 DOI: 10.3390/toxins13070449] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Revised: 06/18/2021] [Accepted: 06/23/2021] [Indexed: 01/13/2023] Open
Abstract
Many bacteria secrete toxic protein complexes that modify and disrupt essential processes in the infected cell that can lead to cell death. To conduct their action, these toxins often need to cross the cell membrane and reach a specific substrate inside the cell. The investigation of these protein complexes is essential not only for understanding their biological functions but also for the rational design of targeted drug delivery vehicles that must navigate across the cell membrane to deliver their therapeutic payload. Despite the immense advances in experimental techniques, the investigations of the toxin entry mechanism have remained challenging. Computer simulations are robust complementary tools that allow for the exploration of biological processes in exceptional detail. In this review, we first highlight the strength of computational methods, with a special focus on all-atom molecular dynamics, coarse-grained, and mesoscopic models, for exploring different stages of the toxin protein entry mechanism. We then summarize recent developments that are significantly advancing our understanding, notably of the glycolipid–lectin (GL-Lect) endocytosis of bacterial Shiga and cholera toxins. The methods discussed here are also applicable to the design of membrane-penetrating nanoparticles and the study of the phenomenon of protein phase separation at the surface of the membrane. Finally, we discuss other likely routes for future development.
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Affiliation(s)
- Weria Pezeshkian
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, 9712 Groningen, The Netherlands
- Correspondence:
| | - Julian C. Shillcock
- Blue Brain Project, Laboratory of Molecular and Chemical Biology of Neurodegeneration, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland;
| | - John H. Ipsen
- MEMPHYS/PhyLife, Department of Physics, Chemistry and Pharmacy (FKF), University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark;
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Vasquez-Montes V, Ladokhin AS. Expanding MPEx Hydropathy Analysis to Account for Electrostatic Contributions to Protein Interactions with Anionic Membranes. J Membr Biol 2021; 254:109-117. [PMID: 33564913 DOI: 10.1007/s00232-021-00170-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 01/05/2021] [Indexed: 12/21/2022]
Abstract
Hydropathy plots are a crucial tool to guide experimental design, as they generate predictions of protein-membrane interactions and their bilayer topology. The predictions are based on experimentally determined hydrophobicity scales, which provide an estimate for the propensity and stability of these interactions. A significant improvement to the accuracy of hydropathy analyses was provided by the development of the popular Wimley-White interfacial and octanol hydrophobicity scales. These scales have been previously incorporated into the freely available MPEx (Membrane Protein Explorer) online application. Here, we introduce a substantial update to MPEx that allows for the consideration of electrostatic contributions to the bilayer partitioning free energy. This component originates from the Coulombic attraction or repulsion of charges between proteins and membranes. Its inclusion in hydropathy calculations increases the accuracy of hydropathy plot predictions and extends their use to more complex systems (i.e., anionic membranes). We illustrate the application of this analysis to studies on the membrane selectivity of antimicrobial peptides, the membrane partitioning of ion-channel gating modifiers, and the amyloid proteins α-synuclein and Tau, as well as pH-dependent bilayer interactions of diphtheria toxin and apoptotic inhibitor Bcl-xL.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA.
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA.
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10
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Ladokhin AS, Kyrychenko A, Rodnin MV, Vasquez-Montes V. Conformational switching, refolding and membrane insertion of the diphtheria toxin translocation domain. Methods Enzymol 2021; 649:341-370. [PMID: 33712192 DOI: 10.1016/bs.mie.2020.12.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Diphtheria toxin is among many bacterial toxins that utilize the endosomal pathway of cellular entry, which is ensured by the bridging of the endosomal membrane by the toxin's translocation (T) domain. Endosomal acidification triggers a series of conformational changes of the T-domain, that take place first in aqueous and subsequently in membranous milieu. These rearrangements ultimately result in establishing membrane-inserted conformation(s) and translocation of the catalytic moiety of the toxin into the cytoplasm. We discuss here the strategy for combining site-selective labeling with various spectroscopic methods to characterize structural and thermodynamic aspects of protonation-dependent conformational switching and membrane insertion of the diphtheria toxin T-domain. Among the discussed methods are FRET, FCS and depth-dependent fluorescence quenching with lipid-attached bromine atoms and spin probes. The membrane-insertion pathway of the T-domain contains multiple intermediates and is governed by staggered pH-dependent transitions involving protonation of histidines and acidic residues. Presented data demonstrate that the lipid bilayer plays an active part in T-domain functioning and that the so-called Open-Channel State does not constitute the translocation pathway, but is likely to be a byproduct of the translocation. The spectroscopic approaches presented here are broadly applicable to many other systems of physiological and biomedical interest for which conformational changes can lead to membrane insertion (e.g., other bacterial toxins, host defense peptides, tumor-targeting pHLIP peptides and members of Bcl-2 family of apoptotic regulators).
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Affiliation(s)
- Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, Kansas University Medical Center, Kansas City, KS, United States.
| | - Alexander Kyrychenko
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine
| | - Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, Kansas University Medical Center, Kansas City, KS, United States
| | - Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, Kansas University Medical Center, Kansas City, KS, United States
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11
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Rodnin MV, Kashipathy MM, Kyrychenko A, Battaile KP, Lovell S, Ladokhin AS. Structure of the Diphtheria Toxin at Acidic pH: Implications for the Conformational Switching of the Translocation Domain. Toxins (Basel) 2020; 12:toxins12110704. [PMID: 33171806 PMCID: PMC7695028 DOI: 10.3390/toxins12110704] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 10/29/2020] [Accepted: 11/05/2020] [Indexed: 12/28/2022] Open
Abstract
Diphtheria toxin, an exotoxin secreted by Corynebacterium that causes disease in humans by inhibiting protein synthesis, enters the cell via receptor-mediated endocytosis. The subsequent endosomal acidification triggers a series of conformational changes, resulting in the refolding and membrane insertion of the translocation (T-)domain and ultimately leading to the translocation of the catalytic domain into the cytoplasm. Here, we use X-ray crystallography along with circular dichroism and fluorescence spectroscopy to gain insight into the mechanism of the early stages of pH-dependent conformational transition. For the first time, we present the high-resolution structure of the diphtheria toxin at a mildly acidic pH (5–6) and compare it to the structure at neutral pH (7). We demonstrate that neither catalytic nor receptor-binding domains change their structure upon this acidification, while the T-domain undergoes a conformational change that results in the unfolding of the TH2–3 helices. Surprisingly, the TH1 helix maintains its conformation in the crystal of the full-length toxin even at pH 5. This contrasts with the evidence from the new and previously published data, obtained by spectroscopic measurements and molecular dynamics computer simulations, which indicate the refolding of TH1 upon the acidification of the isolated T-domain. The overall results imply that the membrane interactions of the T-domain are critical in ensuring the proper conformational changes required for the preparation of the diphtheria toxin for the cellular entry.
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Affiliation(s)
- Mykola V. Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.V.R.); (A.K.)
| | - Maithri M. Kashipathy
- Protein Structure Laboratory, Shankel Structural Biology Center, University of Kansas, Lawrence, KS 66047, USA; (M.M.K.); (S.L.)
| | - Alexander Kyrychenko
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.V.R.); (A.K.)
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, 61022 Kharkiv, Ukraine
| | - Kevin P. Battaile
- NYX beamline, New York Structural Biology Center, Upton, NY 11973, USA;
| | - Scott Lovell
- Protein Structure Laboratory, Shankel Structural Biology Center, University of Kansas, Lawrence, KS 66047, USA; (M.M.K.); (S.L.)
| | - Alexey S. Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA; (M.V.R.); (A.K.)
- Correspondence: ; Tel.: +1-913-588-0489; Fax: +1-913-588-7440
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12
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Afrose F, Martfeld AN, Greathouse DV, Koeppe RE. Examination of pH dependency and orientation differences of membrane spanning alpha helices carrying a single or pair of buried histidine residues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183501. [PMID: 33130099 DOI: 10.1016/j.bbamem.2020.183501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 10/22/2020] [Accepted: 10/23/2020] [Indexed: 01/08/2023]
Abstract
We have employed the peptide framework of GWALP23 (acetyl-GGALWLALALALALALALWLAGA-amide) to examine the orientation, dynamics and pH dependence of peptides having buried single or pairs of histidine residues. When residue L8 is substituted to yield GWALP23-H8, acetyl-GGALWLAH8ALALALALALWLAGA-amide, the deuterium NMR spectra of 2H-labeled core alanine residues reveal a helix that occupies a single transmembrane orientation in DLPC, or in DMPC at low pH, yet shows multiple states at higher pH or in bilayers of DOPC. Moreover, a single histidine at position 8 or 16 in the GWALP23 framework is sensitive to pH. Titration points are observed near pH 3.5 for the deprotonation of H8 in lipid bilayers of DLPC or DMPC, and for H16 in DOPC. When residues L8 and L16 both are substituted to yield GWALP23-H8,16, the 2H NMR spectra show, interestingly, no titration dependence from pH 2-8, yet bilayer thickness-dependent orientation differences. The helix with H8 and H16 is found to adopt a transmembrane orientation in thin bilayers of DLPC, a combination of transmembrane and surface orientations in DMPC, and then a complete transition to a surface bound orientation in the thicker DPoPC and DOPC lipid bilayers. In the surface orientations, alanine A7 no longer fits within the core helix. These results along with previous studies with different locations of histidine residues suggest that lipid hydrophobic thickness is a first determinant and pH a second determinant for the helical orientation, along with possible side-chain snorkeling, when the His residues are incorporated into the hydrophobic region of a lipid membrane-associated helix.
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Affiliation(s)
- Fahmida Afrose
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Ashley N Martfeld
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
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13
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Purification and Characterization of DT389GCSF Fusion Protein: A Unique Immunotoxin Against the Human Granulocyte-Colony Stimulating Factor Receptor. Int J Pept Res Ther 2020. [DOI: 10.1007/s10989-019-09884-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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14
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Reshetnyak YK, Moshnikova A, Andreev OA, Engelman DM. Targeting Acidic Diseased Tissues by pH-Triggered Membrane-Associated Peptide Folding. Front Bioeng Biotechnol 2020; 8:335. [PMID: 32411684 PMCID: PMC7198868 DOI: 10.3389/fbioe.2020.00335] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Accepted: 03/26/2020] [Indexed: 12/19/2022] Open
Abstract
The advantages of targeted therapy have motivated many efforts to find distinguishing features between the molecular cell surface landscapes of diseased and normal cells. Typically, the features have been proteins, lipids or carbohydrates, but other approaches are emerging. In this discussion, we examine the use of cell surface acidity as a feature that can be exploited by using pH-sensitive peptide folding to target agents to diseased cell surfaces or cytoplasms.
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Affiliation(s)
- Yana K Reshetnyak
- Department of Physics, The University of Rhode Island, Kingston, RI, United States
| | - Anna Moshnikova
- Department of Physics, The University of Rhode Island, Kingston, RI, United States
| | - Oleg A Andreev
- Department of Physics, The University of Rhode Island, Kingston, RI, United States
| | - Donald M Engelman
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
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15
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Delivery systems exploiting natural cell transport processes of macromolecules for intracellular targeting of Auger electron emitters. Nucl Med Biol 2019; 80-81:45-56. [PMID: 31810828 DOI: 10.1016/j.nucmedbio.2019.11.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 10/24/2019] [Accepted: 11/25/2019] [Indexed: 12/17/2022]
Abstract
The presence of Auger electrons (AE) among the decay products of a number of radionuclides makes these radionuclides an attractive means for treating cancer because these short-range electrons can cause significant damage in the immediate vicinity of the decomposition site. Moreover, the extreme locality of the effect provides a potential for selective eradication of cancer cells with minimal damage to adjacent normal cells provided that the delivery of the AE emitter to the most vulnerable parts of the cell can be achieved. Few cellular compartments have been regarded as the desired target site for AE emitters, with the cell nucleus generally recognized as the preferred site for AE decay due to the extreme sensitivity of nuclear DNA to direct damage by radiation of high linear energy transfer. Thus, the advantages of AE emitters for cancer therapy are most likely to be realized by their selective delivery into the nucleus of the malignant cells. To achieve this goal, delivery systems must combine a challenging complex of properties that not only provide cancer cell preferential recognition but also cell entry followed by transport into the cell nucleus. A promising strategy for achieving this is the recruitment of natural cell transport processes of macromolecules, involved in each of the aforementioned steps. To date, a number of constructs exploiting intracellular transport systems have been proposed for AE emitter delivery to the nucleus of a targeted cell. An example of such a multifunctional vehicle that provides smart step-by-step delivery is the so-called modular nanotransporter, which accomplishes selective recognition, binding, internalization, and endosomal escape followed by nuclear import of the delivered radionuclide. The current review will focus on delivery systems utilizing various intracellular transport pathways and their combinations in order to provide efficient targeting of AE to the cancer cell nucleus.
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16
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Vasquez-Montes V, Gerhart J, Thévenin D, Ladokhin AS. Divalent Cations and Lipid Composition Modulate Membrane Insertion and Cancer-Targeting Action of pHLIP. J Mol Biol 2019; 431:5004-5018. [PMID: 31689432 DOI: 10.1016/j.jmb.2019.10.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2019] [Revised: 10/24/2019] [Accepted: 10/24/2019] [Indexed: 02/06/2023]
Abstract
The pH-Low Insertion Peptide (pHLIP) has emerged as an important tool for targeting cancer cells; it has been assumed that its targeting mechanism depends solely on the mild acidic environment surrounding tumors. Here, we examine the role of Ca2+ and Mg2+ on pHLIP's insertion, cellular targeting, and drug delivery. We demonstrate that physiologically relevant concentrations of either cation can shift the protonation-dependent transition by up to several pH units toward basic pH and induce substantial protonation-independent transmembrane insertion of pHLIP at pH as high as 10. Consistent with these results, the ability of pHLIP to deliver the cytotoxic compound monomethyl-auristatin-F to HeLa cells is increased several fold in presence of Ca2+. Complementary measurements with model membranes confirmed this Ca2+/Mg2+-dependent membrane-insertion mechanism. The magnitude of this alternative Ca2+/Mg2+-dependent effect is also modulated by lipid composition-specifically by the presence of phosphatidylserine-providing new clues to pHLIP's unique tumor-targeting ability in vivo. These results exemplify the complex coupling between protonation of anionic residues and lipid-selective targeting by divalent cations, which is relevant to the general signaling on membrane interfaces.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS, 66160, USA
| | - Janessa Gerhart
- Department of Chemistry, Lehigh University, 6 East Packer Avenue, Bethlehem, PA, 18015, USA
| | - Damien Thévenin
- Department of Chemistry, Lehigh University, 6 East Packer Avenue, Bethlehem, PA, 18015, USA
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS, 66160, USA.
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17
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Sannigrahi A, Nandi I, Chall S, Jawed JJ, Halder A, Majumdar S, Karmakar S, Chattopadhyay K. Conformational Switch Driven Membrane Pore Formation by Mycobacterium Secretory Protein MPT63 Induces Macrophage Cell Death. ACS Chem Biol 2019; 14:1601-1610. [PMID: 31241303 DOI: 10.1021/acschembio.9b00327] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Virulent Mycobacterium tuberculosis (MTB) strains cause cell death of macrophages (Mϕ) inside TB granuloma using a mechanism which is not well understood. Many bacterial systems utilize toxins to induce host cell damage, which occurs along with immune evasion. These toxins often use chameleon sequences to generate an environment-sensitive conformational switch, facilitating the process of infection. The presence of toxins is not yet known for MTB. Here, we show that MTB-secreted immunogenic MPT63 protein undergoes a switch from β-sheet to helix in response to mutational and environmental stresses. MPT63 in its helical form creates pores in both synthetic and Mϕ membranes, while the native β-sheet protein remains inert toward membrane interactions. Using fluorescence correlation spectroscopy and atomic force microscopy, we show further that the helical form undergoes self-association to produce toxic oligomers of different morphology. Trypan blue and flow cytometry analyses reveal that the helical state can be utilized by MTB for killing Mϕ cells. Collectively, our study emphasizes for the first time a toxin-like behavior of MPT63 induced by an environment-dependent conformational switch, resulting in membrane pore formation by toxic oligomers and Mϕ cell death.
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Affiliation(s)
- Achinta Sannigrahi
- Structural Biology & Bio-Informatics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mallick Road, Kolkata 700032, India
| | - Indrani Nandi
- Structural Biology & Bio-Informatics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mallick Road, Kolkata 700032, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Sayantani Chall
- Structural Biology & Bio-Informatics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mallick Road, Kolkata 700032, India
| | | | - Animesh Halder
- Department of Physics, Jadavpur University, 188, Raja S. C. Mallick Road, Kolkata 700032, India
| | - Subrata Majumdar
- Department of Molecular Medicine, Bose Institute, Kolkata 700054, India
| | - Sanat Karmakar
- Department of Physics, Jadavpur University, 188, Raja S. C. Mallick Road, Kolkata 700032, India
| | - Krishnananda Chattopadhyay
- Structural Biology & Bio-Informatics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mallick Road, Kolkata 700032, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
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18
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Pitard I, Malliavin TE. Structural Biology and Molecular Modeling to Analyze the Entry of Bacterial Toxins and Virulence Factors into Host Cells. Toxins (Basel) 2019; 11:toxins11060369. [PMID: 31238550 PMCID: PMC6628625 DOI: 10.3390/toxins11060369] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 06/17/2019] [Accepted: 06/18/2019] [Indexed: 12/26/2022] Open
Abstract
Understanding the functions and mechanisms of biological systems is an outstanding challenge. One way to overcome it is to combine together several approaches such as molecular modeling and experimental structural biology techniques. Indeed, the interplay between structural and dynamical properties of the system is crucial to unravel the function of molecular machinery’s. In this review, we focus on how molecular simulations along with structural information can aid in interpreting biological data. Here, we examine two different cases: (i) the endosomal translocation toxins (diphtheria, tetanus, botulinum toxins) and (ii) the activation of adenylyl cyclase inside the cytoplasm (edema factor, CyA, ExoY).
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Affiliation(s)
- Irène Pitard
- Unité de Bioinformatique Structurale, Institut Pasteur and CNRS UMR3528, 75015 Paris, France.
- Centre de Bioinformatique, Biostatistique et Biologie Intégrative, Institut Pasteur and CNRS USR3756, 75015 Paris, France.
- Sorbonne Université, Collège Doctoral, Ecole Doctorale Complexité du Vivant, 75005 Paris, France.
| | - Thérèse E Malliavin
- Unité de Bioinformatique Structurale, Institut Pasteur and CNRS UMR3528, 75015 Paris, France.
- Centre de Bioinformatique, Biostatistique et Biologie Intégrative, Institut Pasteur and CNRS USR3756, 75015 Paris, France.
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19
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Vasquez-Montes V, Vargas-Uribe M, Pandey NK, Rodnin MV, Langen R, Ladokhin AS. Lipid-modulation of membrane insertion and refolding of the apoptotic inhibitor Bcl-xL. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:691-700. [PMID: 31004798 DOI: 10.1016/j.bbapap.2019.04.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 04/16/2019] [Indexed: 02/07/2023]
Abstract
Bcl-xL is a member of the Bcl-2 family of apoptotic regulators, responsible for inhibiting the permeabilization of the mitochondrial outer membrane, and a promising anti-cancer target. Bcl-xL exists in the following conformations, each believed to play a role in the inhibition of apoptosis: (a) a soluble folded conformation, (b) a membrane-anchored (by its C-terminal α8 helix) form, which retains the same fold as in solution and (c) refolded membrane-inserted conformations, for which no structural data are available. Previous studies established that in the cell Bcl-xL exists in a dynamic equilibrium between soluble and membranous states, however, no direct evidence exists in support of either anchored or inserted conformation of the membranous state in vivo. In this in vitro study, we employed a combination of fluorescence and EPR spectroscopy to characterize structural features of the bilayer-inserted conformation of Bcl-xL and the lipid modulation of its membrane insertion transition. Our results indicate that the core hydrophobic helix α6 inserts into the bilayer without adopting a transmembrane orientation. This insertion disrupts the packing of Bcl-xL and releases the regulatory N-terminal BH4 domain (α1) from the rest of the protein structure. Our data demonstrate that both insertion and refolding of Bcl-xL are modulated by lipid composition, which brings the apparent pKa of insertion to the threshold of physiological pH. We hypothesize that conformational rearrangements associated with the bilayer insertion of Bcl-xL result in its switching to a so-called non-canonical mode of apoptotic inhibition. Presented results suggest that the alteration in lipid composition before and during apoptosis can serve as an additional factor regulating the permeabilization of the mitochondrial outer membrane.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Mauricio Vargas-Uribe
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Nitin K Pandey
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Ralf Langen
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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20
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Scott HL, Heberle FA, Katsaras J, Barrera FN. Phosphatidylserine Asymmetry Promotes the Membrane Insertion of a Transmembrane Helix. Biophys J 2019; 116:1495-1506. [PMID: 30954213 DOI: 10.1016/j.bpj.2019.03.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 02/13/2019] [Accepted: 03/06/2019] [Indexed: 11/18/2022] Open
Abstract
The plasma membrane (PM) contains an asymmetric distribution of lipids between the inner and outer bilayer leaflets. A lipid of special interest in eukaryotic membranes is the negatively charged phosphatidylserine (PS). In healthy cells, PS is actively sequestered to the inner leaflet of the PM, but PS redistributes to the outer leaflet when the cell is damaged or at the onset of apoptosis. However, the influence of PS asymmetry on membrane protein structure and folding are poorly understood. The pH low insertion peptide (pHLIP) adsorbs to the membrane surface at a neutral pH, but it inserts into the membrane at an acidic pH. We have previously observed that in symmetric vesicles, PS affects the membrane insertion of pHLIP by lowering the pH midpoint of insertion. Here, we studied the effect of PS asymmetry on the membrane interaction of pHLIP. We developed a modified protocol to create asymmetric vesicles containing PS and employed Annexin V labeled with an Alexa Fluor 568 fluorophore as a new probe to quantify PS asymmetry. We observed that the membrane insertion of pHLIP was promoted by the asymmetric distribution of negatively charged PS, which causes a surface charge difference between bilayer leaflets. Our results indicate that lipid asymmetry can modulate the formation of an α-helix on the membrane. A corollary is that model studies using symmetric bilayers to mimic the PM may fail to capture important aspects of protein-membrane interactions.
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Affiliation(s)
- Haden L Scott
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Frederick A Heberle
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center-a Joint Institute for Neutron Sciences, Oak Ridge, Tennessee
| | - John Katsaras
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center-a Joint Institute for Neutron Sciences, Oak Ridge, Tennessee; Large Scale Structures Group, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics, Brock University, St. Catharines, Ontario, Canada
| | - Francisco N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee.
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21
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Lei Y, Zhao F, Shao J, Li Y, Li S, Chang H, Zhang Y. Application of built-in adjuvants for epitope-based vaccines. PeerJ 2019; 6:e6185. [PMID: 30656066 PMCID: PMC6336016 DOI: 10.7717/peerj.6185] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 11/29/2018] [Indexed: 12/21/2022] Open
Abstract
Several studies have shown that epitope vaccines exhibit substantial advantages over conventional vaccines. However, epitope vaccines are associated with limited immunity, which can be overcome by conjugating antigenic epitopes with built-in adjuvants (e.g., some carrier proteins or new biomaterials) with special properties, including immunologic specificity, good biosecurity and biocompatibility, and the ability to vastly improve the immune response of epitope vaccines. When designing epitope vaccines, the following types of built-in adjuvants are typically considered: (1) pattern recognition receptor ligands (i.e., toll-like receptors); (2) virus-like particle carrier platforms; (3) bacterial toxin proteins; and (4) novel potential delivery systems (e.g., self-assembled peptide nanoparticles, lipid core peptides, and polymeric or inorganic nanoparticles). This review primarily discusses the current and prospective applications of these built-in adjuvants (i.e., biological carriers) to provide some references for the future design of epitope-based vaccines.
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Affiliation(s)
- Yao Lei
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Furong Zhao
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Junjun Shao
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Yangfan Li
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Shifang Li
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Huiyun Chang
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
| | - Yongguang Zhang
- State Key Laboratory of Veterinary Etiological Biology, OIE/National Foot-and-Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China.,Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China
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22
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Tatulian SA, Kandel N. Membrane Pore Formation by Peptides Studied by Fluorescence Techniques. Methods Mol Biol 2019; 2003:449-464. [PMID: 31218629 DOI: 10.1007/978-1-4939-9512-7_19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Pore formation in cellular membranes by pathogen-derived proteins is a mechanism utilized by a set of microbes to exert their cytotoxic effect. On the other hand, the host cells have developed a defense mechanism to produce antimicrobial peptides to kill the pathogens by a similar, membrane perforation mechanism. Furthermore, certain endogenous proteins or peptides kill the parent cells through membrane permeabilization. Analysis of the molecular details of membrane pore formation is often conducted using artificial systems, such as bilayer lipid membranes and synthetic peptides. This chapter describes two fluorescence-based methods to study peptide-induced membrane leakage. One method involves preparation of lipid vesicles loaded with a fluorophore (e.g., calcein or carboxyfluorescein) at a self-quenching concentration. If the externally added peptide forms relatively large pores (≥1 nm in diameter), the fluorophore leaks out and undergoes dequenching, resulting in time-dependent increase in fluorescence. The other method is designed to monitor smaller pores (<1 nm in diameter). It involves preparation of vesicles in a Ca2+-less buffer, containing a Ca2+-dependent fluorophore, such as Quin-2. Removal of external Quin-2 by a desalting column and addition of an appropriate concentration of CaCl2 externally sequesters Quin-2 and Ca2+ ions by the vesicle membrane. Addition of the pore-forming peptide to these vesicles results in membrane permeabilization, Ca2+ influx and binding to Quin-2. In both cases, the kinetics of the increase of fluorescence and its equilibrium levels allow quantitative analysis of the pore formation mechanism.
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Affiliation(s)
- Suren A Tatulian
- Department of Physics, University of Central Florida, Orlando, FL, USA.
| | - Nabin Kandel
- Department of Physics, University of Central Florida, Orlando, FL, USA
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23
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A viral-fusion-peptide-like molecular switch drives membrane insertion of botulinum neurotoxin A1. Nat Commun 2018; 9:5367. [PMID: 30560862 PMCID: PMC6299077 DOI: 10.1038/s41467-018-07789-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 11/22/2018] [Indexed: 11/09/2022] Open
Abstract
Botulinum neurotoxin (BoNT) delivers its protease domain across the vesicle membrane to enter the neuronal cytosol upon vesicle acidification. This process is mediated by its translocation domain (HN), but the molecular mechanism underlying membrane insertion of HN remains poorly understood. Here, we report two crystal structures of BoNT/A1 HN that reveal a novel molecular switch (termed BoNT-switch) in HN, where buried α-helices transform into surface-exposed hydrophobic β-hairpins triggered by acidic pH. Locking the BoNT-switch by disulfide trapping inhibited the association of HN with anionic liposomes, blocked channel formation by HN, and reduced the neurotoxicity of BoNT/A1 by up to ~180-fold. Single particle counting studies showed that an acidic environment tends to promote BoNT/A1 self-association on liposomes, which is partly regulated by the BoNT-switch. These findings suggest that the BoNT-switch flips out upon exposure to the acidic endosomal pH, which enables membrane insertion of HN that subsequently leads to LC delivery. The translocation domain (HN) of Botulinum neurotoxins (BoNTs) mediates the delivery of the BoNT light chain (LC) into neuronal cytosol. Here the authors provide insights into HN membrane insertion by determining the crystal structure of BoNT/A1 HN at acidic pH, which reveals a molecular switch in HN, where buried α-helices are transformed into surface-exposed hydrophobic β-hairpins.
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24
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Siahmazgi MG, Khalili MAN, Ahmadpour F, Khodadadi S, Zeinoddini M. In Silico Design of Fusion Toxin DT 389GCSF and a Comparative Study. Curr Comput Aided Drug Des 2018; 16:238-244. [PMID: 30318000 DOI: 10.2174/1573409914666181012151242] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2018] [Revised: 09/27/2018] [Accepted: 10/06/2018] [Indexed: 11/22/2022]
Abstract
BACKGROUND Chemotherapy and radiotherapy have negative effects on normal tissues and they are very expensive and lengthy treatments. These disadvantages have recently attracted researchers to the new methods that specifically affect cancerous tissues and have lower damage to normal tissues. One of these methods is the use of intelligent recombinant fusion toxin. The fusion toxin DTGCSF, which consists of linked Diphtheria Toxin (DT) and Granulocyte Colony Stimulate Factor (GCSF), was first studied by Chadwick et al. in 1993 where HATPL linker provided the linking sequence between GCSF and the 486 amino acid sequences of DT. METHODS In this study, the fusion toxin DT389GCSF is evaluated for functional structure in silico. With the idea of the commercial fusion toxin of Ontak, the DT in this fusion protein is designed incomplete for 389 amino acids and is linked to the beginning of the GCSF cytokine via the SG4SM linker (DT389GCSF). The affinity of the DT389GCSF as a ligand with GCSF-R as receptor was compared with DT486GCSF as a ligand with GCSF-R as receptor. Both DT486GCSF and its receptor GCSF-R have been modeled by Easy Modeler2 software. Our fusion protein (DT389GCSF) and GCSF-R are modeled through Modeller software; all of the structures were confirmed by server MDWEB and VMD software. Then, the interaction studies between two proteins are done using protein-protein docking (HADDOCK 2.2 web server) for both the fusion protein in this study and DT486GCSF. RESULTS The HADDOCK results demonstrate that the interaction of DT389GCSF with GCSF-R is very different and has a more powerful interaction than DT486GCSF with GCSF-R. CONCLUSION HADDOCK web server is operative tools for evaluation of protein-protein interactions, therefore, in silico study of DT389GCSF will help with studying the function and the structure of these molecules. Moreover, DT389GCSF may have important new therapeutic applications.
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Affiliation(s)
| | | | - Fathollah Ahmadpour
- Trauma Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran
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25
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Abstract
RNA interference (RNAi) is a fundamental cellular process for the posttranscriptional regulation of gene expression. RNAi can exogenously be modulated by small RNA oligonucleotides, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), or by antisense oligonucleotides. These small oligonucleotides provided the scientific community with powerful and versatile tools to turn off the expression of genes of interest, and hold out the promise of new therapeutic solutions against a wide range of gene-associated pathologies. However, unmodified nucleic acids are highly instable in biological systems, and their weak interaction with plasma proteins confers an unfavorable pharmacokinetics. In this review, we first provide an overview of the most efficient chemical strategies that, over the past 30 years, have been used to significantly improve the therapeutic potential of oligonucleotides. Oligonucleotides targeting and delivery technologies are then presented, including covalent conjugates between oligonucleotides and targeting ligand, and noncovalent association with lipid or polymer nanoparticles. Finally, we specifically focus on the endosomal escape step, which represents a major stumbling block for the effective use of oligonucleotides as therapeutic agents. The need for approaches to quantitatively measure endosomal escape and cytosolic arrival of biomolecules is discussed in the context of the development of efficient oligonucleotide targeting and delivery vectors.
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Affiliation(s)
- Ludger Johannes
- Institut Curie, PSL Research University , Cellular and Chemical Biology, U1143 INSERM, UMR3666 CNRS, Paris, France
| | - Marco Lucchino
- Institut Curie, PSL Research University , Cellular and Chemical Biology, U1143 INSERM, UMR3666 CNRS, Paris, France
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26
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Tang Y, Romano FB, Breña M, Heuck AP. The Pseudomonas aeruginosa type III secretion translocator PopB assists the insertion of the PopD translocator into host cell membranes. J Biol Chem 2018; 293:8982-8993. [PMID: 29685888 DOI: 10.1074/jbc.ra118.002766] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/10/2018] [Indexed: 11/06/2022] Open
Abstract
Many Gram-negative bacterial pathogens use a type III secretion system to infect eukaryotic cells. The injection of bacterial toxins or protein effectors via this system is accomplished through a plasma membrane channel formed by two bacterial proteins, termed translocators, whose assembly and membrane-insertion mechanisms are currently unclear. Here, using purified proteins we demonstrate that the translocators PopB and PopD in Pseudomonas aeruginosa assemble heterodimers in membranes, leading to stably inserted hetero-complexes. Using site-directed fluorescence labeling with an environment-sensitive probe, we found that hydrophobic segments in PopD anchor the translocator to the membrane, but without adopting a typical transmembrane orientation. A fluorescence dual-quenching assay revealed that the presence of PopB changes the conformation adopted by PopD segments in membranes. Furthermore, analysis of PopD's interaction with human cell membranes revealed that PopD adopts a distinctive conformation when PopB is present. An N-terminal region of PopD is only exposed to the host cytosol when PopB is present. We conclude that PopB assists with the proper insertion of PopD in cell membranes, required for the formation of a functional translocon and host infection.
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Affiliation(s)
- Yuzhou Tang
- From the Program in Molecular and Cellular Biology and
| | | | - Mariana Breña
- From the Program in Molecular and Cellular Biology and
| | - Alejandro P Heuck
- From the Program in Molecular and Cellular Biology and .,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003
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27
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Lipkin R, Lazaridis T. Computational studies of peptide-induced membrane pore formation. Philos Trans R Soc Lond B Biol Sci 2018. [PMID: 28630158 DOI: 10.1098/rstb.2016.0219] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
A variety of peptides induce pores in biological membranes; the most common ones are naturally produced antimicrobial peptides (AMPs), which are small, usually cationic, and defend diverse organisms against biological threats. Because it is not possible to observe these pores directly on a molecular scale, the structure of AMP-induced pores and the exact sequence of steps leading to their formation remain uncertain. Hence, these questions have been investigated via molecular modelling. In this article, we review computational studies of AMP pore formation using all-atom, coarse-grained, and implicit solvent models; evaluate the results obtained and suggest future research directions to further elucidate the pore formation mechanism of AMPs.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.
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Affiliation(s)
- Richard Lipkin
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA.,Graduate Program in Chemistry, The Graduate Center, City University of New York, 365 Fifth Avenue, New York, NY 10016, USA
| | - Themis Lazaridis
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA
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28
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Refining Protein Penetration into the Lipid Bilayer Using Fluorescence Quenching and Molecular Dynamics Simulations: The Case of Diphtheria Toxin Translocation Domain. J Membr Biol 2018; 251:379-391. [PMID: 29550876 DOI: 10.1007/s00232-018-0030-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 03/11/2018] [Indexed: 12/23/2022]
Abstract
Dynamic disorder of the lipid bilayer presents a challenge for establishing structure-function relationships in membranous systems. The resulting structural heterogeneity is especially evident for peripheral and spontaneously inserting membrane proteins, which are not constrained by the well-defined transmembrane topology and exert their action in the context of intimate interaction with lipids. Here, we propose a concerted approach combining depth-dependent fluorescence quenching with Molecular Dynamics simulation to decipher dynamic interactions of membrane proteins with the lipid bilayers. We apply this approach to characterize membrane-mediated action of the diphtheria toxin translocation domain. First, we use a combination of the steady-state and time-resolved fluorescence spectroscopy to characterize bilayer penetration of the NBD probe selectively attached to different sites of the protein into membranes containing lipid-attached nitroxyl quenching groups. The constructed quenching profiles are analyzed with the Distribution Analysis methodology allowing for accurate determination of transverse distribution of the probe. The results obtained for 12 NBD-labeled single-Cys mutants are consistent with the so-called Open-Channel topology model. The experimentally determined quenching profiles for labeling sites corresponding to L350, N373, and P378 were used as initial constraints for positioning TH8-9 hairpin into the lipid bilayer for Molecular Dynamics simulation. Finally, we used alchemical free energy calculations to characterize protonation of E362 in soluble translocation domain and membrane-inserted conformation of its TH8-9 fragment. Our results indicate that membrane partitioning of the neutral E362 is more favorable energetically (by ~ 6 kcal/mol), but causes stronger perturbation of the bilayer, than the charged E362.
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29
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Ramadugu VSK, Di Mauro GM, Ravula T, Ramamoorthy A. Polymer nanodiscs and macro-nanodiscs of a varying lipid composition. Chem Commun (Camb) 2018; 53:10824-10826. [PMID: 28926036 DOI: 10.1039/c7cc06409h] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Polymer lipid nanodiscs have enabled some exciting structural biology and nanobiotechnology applications. The use of a small molecular weight polymer (SMA-EA) has been demonstrated to dramatically increase the size of nanodiscs (up to ∼60 nm diameter). Here, we report the first demonstration of the formation of macro-nanodiscs for a variety of lipids, and solid-state NMR experiments utilizing their magnetic-alignment properties.
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30
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Wittchen M, Busche T, Gaspar AH, Lee JH, Ton-That H, Kalinowski J, Tauch A. Transcriptome sequencing of the human pathogen Corynebacterium diphtheriae NCTC 13129 provides detailed insights into its transcriptional landscape and into DtxR-mediated transcriptional regulation. BMC Genomics 2018; 19:82. [PMID: 29370758 PMCID: PMC5784534 DOI: 10.1186/s12864-018-4481-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 01/16/2018] [Indexed: 12/27/2022] Open
Abstract
Background The human pathogen Corynebacterium diphtheriae is the causative agent of diphtheria. In the 1990s a large diphtheria outbreak in Eastern Europe was caused by the strain C. diphtheriae NCTC 13129. Although the genome was sequenced more than a decade ago, not much is known about its transcriptome. Our aim was to use transcriptome sequencing (RNA-Seq) to close this knowledge gap and gain insights into the transcriptional landscape of a C. diphtheriae tox+ strain. Results We applied two different RNA-Seq techniques, one to retrieve 5′-ends of primary transcripts and the other to characterize the whole transcriptional landscape in order to gain insights into various features of the C. diphtheriae NCTC 13129 transcriptome. By examining the data we identified 1656 transcription start sites (TSS), of which 1202 were assigned to genes and 454 to putative novel transcripts. By using the TSS data promoter regions recognized by the housekeeping sigma factor σA and its motifs were analyzed in detail, revealing a well conserved −10 but an only weakly conserved −35 motif, respectively. Furthermore, with the TSS data 5’-UTR lengths were explored. The observed 5’-UTRs range from zero length (leaderless transcripts), which make up 20% of all genes, up to over 450 nt long leaders, which may harbor regulatory functions. The C. diphtheriae transcriptome consists of 471 operons which are further divided into 167 sub-operon structures. In a differential expression analysis approach, we discovered that genetic disruption of the iron-sensing transcription regulator DtxR, which controls expression of diphtheria toxin (DT), causes a strong influence on general gene expression. Nearly 15% of the genome is differentially transcribed, indicating that DtxR might have other regulatory functions in addition to regulation of iron metabolism and DT. Furthermore, our findings shed light on the transcriptional landscape of the DT encoding gene tox and present evidence for two tox antisense RNAs, which point to a new way of transcriptional regulation of toxin production. Conclusions This study presents extensive insights into the transcriptome of C. diphtheriae and provides a basis for future studies regarding gene characterization, transcriptional regulatory networks, and regulation of the tox gene in particular. Electronic supplementary material The online version of this article (10.1186/s12864-018-4481-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Manuel Wittchen
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
| | - Tobias Busche
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany.,Institute for Biology-Microbiology, Freie Universität Berlin, D-14195, Berlin, Germany
| | - Andrew H Gaspar
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, USA
| | - Ju Huck Lee
- Department of Microbiology & Molecular Genetics, University of Texas McGovern Medical School at Houston, Houston, USA.,Present address: Biological Resource Center, Korea Research Institute of Bioscience and Biotechnology, 181 Ipsin-gil, Jeollabuk-do, 56212, Republic of Korea
| | - Hung Ton-That
- Department of Microbiology & Molecular Genetics, University of Texas McGovern Medical School at Houston, Houston, USA
| | - Jörn Kalinowski
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany.
| | - Andreas Tauch
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
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31
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Rampersaud R, Lewis EL, LaRocca TJ, Ratner AJ. Environmental pH modulates inerolysin activity via post-binding blockade. Sci Rep 2018; 8:1542. [PMID: 29367601 PMCID: PMC5784117 DOI: 10.1038/s41598-018-19994-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 01/11/2018] [Indexed: 11/29/2022] Open
Abstract
The cholesterol dependent cytolysins (CDCs) are a family of pore-forming toxins produced by a wide range of bacteria. Some CDCs are important virulence factors for their cognate organisms, but their activity must be tightly regulated to ensure they operate at appropriate times and within the appropriate subcellular compartments. pH-dependent activity has been described for several CDCs, but the mechanism of such regulation has been studied in depth only for listeriolysin O (LLO), which senses environmental pH through a triad of acidic residues that mediate protein unfolding. Here we present data supporting a distinct mechanism for pH-dependence for inerolysin (INY), the CDC produced by Lactobacillus iners. Inerolysin (INY) has an acidic pH optimum with loss of activity at neutral pH. INY pH-dependence is characterized by reversible loss of pore formation with preservation of membrane binding. Fluorescent membrane probe assays indicated that INY insertion into host cell membranes, but not oligomerization, was defective at neutral pH. These data support the existence of a newly appreciated form of CDC pH-dependence functioning at a late stage of pore formation.
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Affiliation(s)
- Ryan Rampersaud
- College of Physicians & Surgeons, Columbia University, New York, NY, USA.,Department of Psychiatry, University of California, San Francisco, CA, USA
| | - Emma L Lewis
- College of Physicians & Surgeons, Columbia University, New York, NY, USA.,Perelman School of Medicine, University of Pennsylvania, Pennsylvania, PA, USA
| | - Timothy J LaRocca
- College of Physicians & Surgeons, Columbia University, New York, NY, USA.,Department of Basic & Clinical Sciences, Albany College of Pharmacy and Health Sciences, Albany, NY, USA
| | - Adam J Ratner
- College of Physicians & Surgeons, Columbia University, New York, NY, USA. .,Department of Pediatrics, New York University School of Medicine, New York, NY, USA. .,Department of Microbiology, New York University School of Medicine, New York, NY, USA.
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32
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Vasquez-Montes V, Gerhart J, King KE, Thévenin D, Ladokhin AS. Comparison of lipid-dependent bilayer insertion of pHLIP and its P20G variant. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:534-543. [PMID: 29138065 DOI: 10.1016/j.bbamem.2017.11.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 10/18/2017] [Accepted: 11/10/2017] [Indexed: 02/07/2023]
Abstract
The ability of the pH-Low Insertion Peptide (pHLIP) to insert into lipid membranes in a transbilayer conformation makes it an important tool for targeting acidic diseased tissues. pHLIP can also serve as a model template for thermodynamic studies of membrane insertion. We use intrinsic fluorescence and circular dichroism spectroscopy to examine the effect of replacing pHLIP's central proline on the pH-triggered lipid-dependent conformational switching of the peptide. We find that the P20G variant (pHLIP-P20G) has a higher helical propensity than the native pHLIP (pHLIP-WT), in both water:organic solvent mixtures and in the presence of lipid bilayers. Spectral shifts of tryptophan fluorescence reveal that with both pHLIP-WT and pHLIP-P20G, the deeply penetrating interfacial form (traditionally called State II) is populated only in pure phosphocholine bilayers. The presence of either anionic lipids or phosphatidylethanolamine leads to a much shallower penetration of the peptide (referred to here as State IIS, for "shallow"). This novel state can be differentiated from soluble state by a reduction in accessibility of tryptophans to acrylamide and by FRET to vesicles doped with Dansyl-PE, but not by a spectral shift in fluorescence emission. FRET experiments indicate free energies for interfacial partitioning range from 6.2 to 6.8kcal/mol and are marginally more favorable for pHLIP-P20G. The effective pKa for the insertion of both peptides depends on the lipid composition, but is always higher for pHLIP-P20G than for pHLIP-WT by approximately one pH unit, which corresponds to a difference of 1.3kcal/mol in free energy of protonation favoring insertion of pHLIP-P20G.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, United States
| | - Janessa Gerhart
- Department of Chemistry, Lehigh University, Bethlehem, PA, 18015, United States
| | - Kelly E King
- Department of Chemistry, Lehigh University, Bethlehem, PA, 18015, United States
| | - Damien Thévenin
- Department of Chemistry, Lehigh University, Bethlehem, PA, 18015, United States
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, United States.
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33
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Ravula T, Hardin NZ, Ramadugu SK, Ramamoorthy A. pH Tunable and Divalent Metal Ion Tolerant Polymer Lipid Nanodiscs. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:10655-10662. [PMID: 28920693 DOI: 10.1021/acs.langmuir.7b02887] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The development and applications of detergent-free membrane mimetics have been the focus for the high-resolution structural and functional studies on membrane proteins. The introduction of lipid nanodiscs has attracted new attention toward the structural biology of membrane proteins and also enabled biomedical applications. Lipid nanodiscs provide a native lipid bilayer environment similar to the cell membrane surrounded by a belt made up of proteins or peptides. Recent studies have shown that the hydrolyzed form of styrene maleic anhydride copolymer (SMA) has the ability to form lipid nanodiscs and has several advantages over protein or peptide based nanodiscs. SMA polymer lipid nanodiscs have become very important for structural biology and nanobiotechnological applications. However, applications of the presently available polymer nanodiscs are limited by their instability toward divalent metal ions and acidic conditions. To overcome the limitations of SMA nanodiscs and to broaden the potential applications of polymer nanodiscs, the present study investigates the tunability of SMA polymer nanodiscs by systematically modifying the maleic acid functional group. The two newly developed polymers and subsequent lipid nanodiscs were characterized using solid-state NMR, FT-IR, TEM, and DLS experiments. The pH dependence and metal ion stability of these nanodiscs were studied using static light scattering and FTIR. The reported polymer nanodiscs exhibit unique pH dependent stability based on the modified functional group and show a high tolerance toward divalent metal ions. We also show these tunable nanodiscs can be used to encapsulate and stabilize a polyphenolic natural product curcumin.
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Affiliation(s)
- Thirupathi Ravula
- Biophysics Program and Department of Chemistry, The University of Michigan , Ann Arbor, Michigan 48109-1055, United States
| | - Nathaniel Z Hardin
- Biophysics Program and Department of Chemistry, The University of Michigan , Ann Arbor, Michigan 48109-1055, United States
| | - Sudheer Kumar Ramadugu
- Biophysics Program and Department of Chemistry, The University of Michigan , Ann Arbor, Michigan 48109-1055, United States
| | - Ayyalusamy Ramamoorthy
- Biophysics Program and Department of Chemistry, The University of Michigan , Ann Arbor, Michigan 48109-1055, United States
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34
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Cellular Entry of the Diphtheria Toxin Does Not Require the Formation of the Open-Channel State by Its Translocation Domain. Toxins (Basel) 2017; 9:toxins9100299. [PMID: 28937631 PMCID: PMC5666346 DOI: 10.3390/toxins9100299] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 09/20/2017] [Accepted: 09/20/2017] [Indexed: 12/30/2022] Open
Abstract
Cellular entry of diphtheria toxin is a multistage process involving receptor targeting, endocytosis, and translocation of the catalytic domain across the endosomal membrane into the cytosol. The latter is ensured by the translocation (T) domain of the toxin, capable of undergoing conformational refolding and membrane insertion in response to the acidification of the endosomal environment. While numerous now classical studies have demonstrated the formation of an ion-conducting conformation-the Open-Channel State (OCS)-as the final step of the refolding pathway, it remains unclear whether this channel constitutes an in vivo translocation pathway or is a byproduct of the translocation. To address this question, we measure functional activity of known OCS-blocking mutants with H-to-Q replacements of C-terminal histidines of the T-domain. We also test the ability of these mutants to translocate their own N-terminus across lipid bilayers of model vesicles. The results of both experiments indicate that translocation activity does not correlate with previously published OCS activity. Finally, we determined the topology of TH5 helix in membrane-inserted T-domain using W281 fluorescence and its depth-dependent quenching by brominated lipids. Our results indicate that while TH5 becomes a transbilayer helix in a wild-type protein, it fails to insert in the case of the OCS-blocking mutant H322Q. We conclude that the formation of the OCS is not necessary for the functional translocation by the T-domain, at least in the histidine-replacement mutants, suggesting that the OCS is unlikely to constitute a translocation pathway for the cellular entry of diphtheria toxin in vivo.
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35
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Scott HL, Westerfield JM, Barrera FN. Determination of the Membrane Translocation pK of the pH-Low Insertion Peptide. Biophys J 2017; 113:869-879. [PMID: 28834723 DOI: 10.1016/j.bpj.2017.06.065] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Revised: 06/13/2017] [Accepted: 06/28/2017] [Indexed: 01/13/2023] Open
Abstract
The pH-low insertion peptide (pHLIP) is a leading peptide technology to target the extracellular acidosis that characterizes solid tumors. The pHLIP binds to lipid membranes, and responds to acidification by undergoing a coupled folding/membrane insertion process. In the final transmembrane state, the C terminus of pHLIP gets exposed to the cytoplasm of the target cell, providing a means to translocate membrane-impermeable drug cargoes across the plasma membrane of cancer cells. There exists a need to develop improved pHLIP variants to target tumors with greater efficiency. Characterization of such variants typically relies on determining the pK parameter, the pH midpoint of peptide insertion into the lipid bilayer. Here we report that the value of the pK can be strongly dependent on the method used for its determination. Membrane insertion of pHLIP involves at least four intermediate states, which are believed to be linked to the staggered titration of key acidic residues. We propose that some spectroscopic methods are influenced more heavily by specific membrane folding intermediates, and as a result yield different pK values. To address this potential problem, we have devised an assay to independently monitor the environment of the two termini of pHLIP. This approach provides insights into the conformation pHLIP adopts immediately before the establishment of the transmembrane configuration. Additionally, our data indicate that the membrane translocation of the C terminus of pHLIP, the folding step more directly relevant to drug delivery, occurs at more acidic pH values than previously considered. Consequently, such a pK difference could have substantial ramifications for assessing the translocation of drug cargoes conjugated to pHLIP.
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Affiliation(s)
- Haden L Scott
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Justin M Westerfield
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Francisco N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee.
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36
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Rodnin MV, Li J, Gross ML, Ladokhin AS. The pH-Dependent Trigger in Diphtheria Toxin T Domain Comes with a Safety Latch. Biophys J 2017; 111:1946-1953. [PMID: 27806276 DOI: 10.1016/j.bpj.2016.09.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Revised: 09/15/2016] [Accepted: 09/19/2016] [Indexed: 01/01/2023] Open
Abstract
Protein-side-chain protonation, coupled to conformational rearrangements, is one way of regulating physiological function caused by changes in protein environment. Specifically, protonation of histidine residues has been implicated in pH-dependent conformational switching in several systems, including the diphtheria toxin translocation (T) domain, which is responsible for the toxin's cellular entry via the endosomal pathway. Our previous studies a) identified protonation of H257 as a major component of the T domain's conformational switch and b) suggested the possibility of a neighboring H223 acting as a modulator, affecting the protonation of H257 and preventing premature conformational changes outside the endosome. To verify this "safety-latch" hypothesis, we report here the pH-dependent folding and membrane interactions of the T domain of the wild-type and that of the H223Q mutant, which lacks the latch. Thermal unfolding of the T domain, measured by circular dichroism, revealed that the reduction in the transition temperature for helical unfolding for an H223Q mutant starts at less acidic conditions (pH <7.5) relative to the wild-type protein (pH <6.5). Hydrogen-deuterium-exchange mass spectrometry demonstrates that the H223Q replacement results in a loss of stability of the amphipathic helices TH1-3 and the hydrophobic core helix TH8 at pH 6.5. That this destabilization occurs in solution correlates well with the pH-range shift for the onset of the membrane permeabilization and translocation activity of the T domain, confirming our initial hypothesis that H223 protonation guards against early refolding. Taken together, these results demonstrate that histidine protonation can fine-tune pH-dependent switching in physiologically relevant systems.
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Affiliation(s)
- Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas
| | - Jing Li
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri
| | - Michael L Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas.
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37
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A Rationally Designed TNF-α Epitope-Scaffold Immunogen Induces Sustained Antibody Response and Alleviates Collagen-Induced Arthritis in Mice. PLoS One 2016; 11:e0163080. [PMID: 27658047 PMCID: PMC5033357 DOI: 10.1371/journal.pone.0163080] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 09/04/2016] [Indexed: 12/29/2022] Open
Abstract
The TNF-α biological inhibitors have significantly improved the clinical outcomes of many autoimmune diseases, in particular rheumatoid arthritis. However, the practical uses are limited due to high costs and the risk of anti-drug antibody responses. Attempts to develop anti-TNF-α vaccines have generated encouraging data in animal models, however, data from clinical trials have not met expectations. In present study, we designed a TNF-α epitope-scaffold immunogen DTNF7 using the transmembrane domain of diphtheria toxin, named DTT as a scaffold. Molecular dynamics simulation shows that the grafted TNF-α epitope is entirely surface-exposed and presented in a native-like conformation while the rigid helical structure of DTT is minimally perturbed, thereby rendering the immunogen highly stable. Immunization of mice with alum formulated DTNF7 induced humoral responses against native TNF-α, and the antibody titer was sustained for more than 6 months, which supports a role of the universal CD4 T cell epitopes of DTT in breaking self-immune tolerance. In a mouse model of rheumatoid arthritis, DTNF7-alum vaccination markedly delayed the onset of collagen-induced arthritis, and reduced incidence as well as clinical score. DTT is presumed safe as an epitope carrier because a catalytic inactive mutant of diphtheria toxin, CRM197 has good clinical safety records as an active vaccine component. Taken all together, we show that DTT-based epitope vaccine is a promising strategy for prevention and treatment of autoimmune diseases.
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38
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Oh KI, Smith-Dupont KB, Markiewicz BN, Gai F. Kinetics of peptide folding in lipid membranes. Biopolymers 2016; 104:281-90. [PMID: 25808575 DOI: 10.1002/bip.22640] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 02/12/2015] [Accepted: 02/14/2015] [Indexed: 12/31/2022]
Abstract
Despite our extensive understanding of water-soluble protein folding kinetics, much less is known about the folding dynamics and mechanisms of membrane proteins. However, recent studies have shown that for relatively simple systems, such as peptides that form a transmembrane α-helix, helical dimer, or helix-turn-helix, it is possible to assess the kinetics of several important steps, including peptide binding to the membrane from aqueous solution, peptide folding on the membrane surface, helix insertion into the membrane, and helix-helix association inside the membrane. Herein, we provide a brief review of these studies and also suggest new initiation and probing methods that could lead to improved temporal and structural resolution in future experiments.
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Affiliation(s)
- Kwang-Im Oh
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104
| | - Kathryn B Smith-Dupont
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | | | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104
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39
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Kyrychenko A. Using fluorescence for studies of biological membranes: a review. Methods Appl Fluoresc 2015; 3:042003. [DOI: 10.1088/2050-6120/3/4/042003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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40
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Role of acidic residues in helices TH8-TH9 in membrane interactions of the diphtheria toxin T domain. Toxins (Basel) 2015; 7:1303-23. [PMID: 25875295 PMCID: PMC4417968 DOI: 10.3390/toxins7041303] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 04/06/2015] [Accepted: 04/07/2015] [Indexed: 01/01/2023] Open
Abstract
The pH-triggered membrane insertion of the diphtheria toxin translocation domain (T domain) results in transferring the catalytic domain into the cytosol, which is relevant to potential biomedical applications as a cargo-delivery system. Protonation of residues is suggested to play a key role in the process, and residues E349, D352 and E362 are of particular interest because of their location within the membrane insertion unit TH8-TH9. We have used various spectroscopic, computational and functional assays to characterize the properties of the T domain carrying the double mutation E349Q/D352N or the single mutation E362Q. Vesicle leakage measurements indicate that both mutants interact with the membrane under less acidic conditions than the wild-type. Thermal unfolding and fluorescence measurements, complemented with molecular dynamics simulations, suggest that the mutant E362Q is more susceptible to acid destabilization because of disruption of native intramolecular contacts. Fluorescence experiments show that removal of the charge in E362Q, and not in E349Q/D352N, is important for insertion of TH8-TH9. Both mutants adopt a final functional state upon further acidification. We conclude that these acidic residues are involved in the pH-dependent action of the T domain, and their replacements can be used for fine tuning the pH range of membrane interactions.
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Knittel D, Savatier A, Upert G, Lortat-Jacob H, Léonetti M. Acidosis increases MHC class II-restricted presentation of a protein endowed with a pH-dependent heparan sulfate-binding ability. THE JOURNAL OF IMMUNOLOGY 2015; 194:3601-11. [PMID: 25754736 DOI: 10.4049/jimmunol.1401902] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 02/08/2015] [Indexed: 02/06/2023]
Abstract
Heparan sulfate proteoglycans (HSPGs) are ubiquitously expressed molecules that participate in numerous biological processes. We previously showed that HSPGs expressed on the surface of APCs can serve as receptors for a hybrid protein containing an HS ligand and an Ag, which leads to more efficient stimulation of Th cells. To investigate whether such behavior is shared by proteins with inherent HS-binding ability, we looked for proteins endowed with this characteristic. We found that diphtheria toxin and its nontoxic mutant, called CRM197, can interact with HS. However, we observed that their binding ability is higher at pH 6 than at pH 7.4. Therefore, as extracellular acidosis occurs during infection by various micro-organisms, we assessed whether HS-binding capacity affects MHC class II-restricted presentation at different pHs. We first observed that pH decrease allows CRM197 binding to HSPG-expressing cells, including APCs. Then, we showed that this interaction enhances Ag uptake and presentation to Th cells. Lastly, we observed that pH decrease does not affect processing and presentation abilities of the APCs. Our findings show that acidic pH causes an HSPG-mediated uptake and an enhancement of T cell stimulation of Ags with the inherent ability to bind HSPGs pH-dependently. Furthermore, they suggest that proteins from micro-organisms with this binding characteristic might be supported more efficiently by the adaptive immune system when acidosis is triggered during infection.
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Affiliation(s)
- Delphine Knittel
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut de Biologie et Technologies de Saclay, Service de Pharmacologie et d'Immunoanalyse, Laboratoire d'Etude et de Recherche en Immunoanalyse, 91191 Gif-Sur-Yvette, France
| | - Alexandra Savatier
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut de Biologie et Technologies de Saclay, Service de Pharmacologie et d'Immunoanalyse, Laboratoire d'Etude et de Recherche en Immunoanalyse, 91191 Gif-Sur-Yvette, France
| | - Grégory Upert
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut de Biologie et Technologies de Saclay, Service d'Ingénierie Moléculaire des Protéines, Laboratoire de Toxinologie Moléculaire et Biotechnologies, 91191 Gif-Sur-Yvette, France
| | - Hugues Lortat-Jacob
- Université Grenoble Alpes, Institut de Biologie Structurale, 38000 Grenoble, France; Centre National de la Recherche Scientifique, Institut de Biologie Structurale, 38000 Grenoble, France; and Commissariat à l'Energie Atomique, Direction des Sciences du Vivant, Institut de Biologie Structurale, 38000 Grenoble, France
| | - Michel Léonetti
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut de Biologie et Technologies de Saclay, Service de Pharmacologie et d'Immunoanalyse, Laboratoire d'Etude et de Recherche en Immunoanalyse, 91191 Gif-Sur-Yvette, France;
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Flores-Canales JC, Vargas-Uribe M, Ladokhin AS, Kurnikova M. Membrane Association of the Diphtheria Toxin Translocation Domain Studied by Coarse-Grained Simulations and Experiment. J Membr Biol 2015; 248:529-43. [PMID: 25650178 DOI: 10.1007/s00232-015-9771-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 01/02/2015] [Indexed: 12/01/2022]
Abstract
Diphtheria toxin translocation (T) domain inserts in lipid bilayers upon acidification of the environment. Computational and experimental studies have suggested that low pH triggers a conformational change of the T-domain in solution preceding membrane binding. The refolded membrane-competent state was modeled to be compact and mostly retain globular structure. In the present work, we investigate how this refolded state interacts with membrane interfaces in the early steps of T-domain's membrane association. Coarse-grained molecular dynamics simulations suggest two distinct membrane-bound conformations of the T-domain in the presence of bilayers composed of a mixture of zwitteronic and anionic phospholipids (POPC:POPG with a 1:3 molar ratio). Both membrane-bound conformations show a common near parallel orientation of hydrophobic helices TH8-TH9 relative to the membrane plane. The most frequently observed membrane-bound conformation is stabilized by electrostatic interactions between the N-terminal segment of the protein and the membrane interface. The second membrane-bound conformation is stabilized by hydrophobic interactions between protein residues and lipid acyl chains, which facilitate deeper protein insertion in the membrane interface. A theoretical estimate of a free energy of binding of a membrane-competent T-domain to the membrane is provided.
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Clostridial pore-forming toxins: Powerful virulence factors. Anaerobe 2014; 30:220-38. [DOI: 10.1016/j.anaerobe.2014.05.014] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 04/16/2014] [Accepted: 05/25/2014] [Indexed: 01/05/2023]
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Li J, Rodnin MV, Ladokhin AS, Gross ML. Hydrogen-deuterium exchange and mass spectrometry reveal the pH-dependent conformational changes of diphtheria toxin T domain. Biochemistry 2014; 53:6849-56. [PMID: 25290210 PMCID: PMC4222528 DOI: 10.1021/bi500893y] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The translocation (T) domain of diphtheria toxin plays a critical role in moving the catalytic domain across the endosomal membrane. Translocation/insertion is triggered by a decrease in pH in the endosome where conformational changes of T domain occur through several kinetic intermediates to yield a final trans-membrane form. High-resolution structural studies are only applicable to the static T-domain structure at physiological pH, and studies of the T-domain translocation pathway are hindered by the simultaneous presence of multiple conformations. Here, we report the application of hydrogen-deuterium exchange mass spectrometry (HDX-MS) for the study of the pH-dependent conformational changes of the T domain in solution. Effects of pH on intrinsic HDX rates were deconvolved by converting the on-exchange times at low pH into times under our "standard condition" (pH 7.5). pH-Dependent HDX kinetic analysis of T domain clearly reveals the conformational transition from the native state (W-state) to a membrane-competent state (W(+)-state). The initial transition occurs at pH 6 and includes the destabilization of N-terminal helices accompanied by the separation between N- and C-terminal segments. The structural rearrangements accompanying the formation of the membrane-competent state expose a hydrophobic hairpin (TH8-9) to solvent, prepare it to insert into the membrane. At pH 5.5, the transition is complete, and the protein further unfolds, resulting in the exposure of its C-terminal hydrophobic TH8-9, leading to subsequent aggregation in the absence of membranes. This solution-based study complements high resolution crystal structures and provides a detailed understanding of the pH-dependent structural rearrangement and acid-induced oligomerization of T domain.
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Affiliation(s)
- Jing Li
- Department of Chemistry, Washington University , St. Louis, Missouri 63130, United States
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Rodnin MV, Ladokhin AS. Membrane translocation assay based on proteolytic cleavage: application to diphtheria toxin T domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:35-40. [PMID: 25291602 DOI: 10.1016/j.bbamem.2014.09.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 09/04/2014] [Accepted: 09/29/2014] [Indexed: 10/24/2022]
Abstract
The function of diphtheria toxin translocation (T) domain is to transfer the catalytic domain across the endosomal membrane upon acidification. The goal of this study was to develop and apply an in vitro functional assay for T domain activity, suitable for investigation of structure-function relationships of translocation across lipid bilayers of various compositions. Traditionally, T domain activity in vitro is estimated by measuring either conductance in planar lipid bilayers or the release of fluorescent markers from lipid vesicles. While an in vivo cell death assay is the most relevant to physiological function, it cannot be applied to studying the effects of pH or membrane lipid composition on translocation. Here we suggest an assay based on cleavage of the N-terminal part of T domain upon translocation into protease-loaded vesicles. A series of control experiment was used to confirm that cleavage occurs inside the vesicle and not as the result of vesicle disruption. Translocation of the N-terminus of the T domain is shown to require the presence of a critical fraction of anionic lipids, which is consistent with our previous biophysical measurements of insertion. Application of the proposed assay to a series of T domain mutants correlated well with the results of cytotoxicity assay.
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Affiliation(s)
- Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, United States
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, United States.
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Vargas-Uribe M, Rodnin MV, Öjemalm K, Holgado A, Kyrychenko A, Nilsson I, Posokhov YO, Makhatadze G, von Heijne G, Ladokhin AS. Thermodynamics of Membrane Insertion and Refolding of the Diphtheria Toxin T-Domain. J Membr Biol 2014; 248:383-94. [PMID: 25281329 DOI: 10.1007/s00232-014-9734-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 09/23/2014] [Indexed: 11/26/2022]
Abstract
The diphtheria toxin translocation (T) domain inserts into the endosomal membrane in response to the endosomal acidification and enables the delivery of the catalytic domain into the cell. The insertion pathway consists of a series of conformational changes that occur in solution and in the membrane and leads to the conversion of a water-soluble state into a transmembrane state. In this work, we utilize various biophysical techniques to characterize the insertion pathway from the thermodynamic perspective. Thermal and chemical unfolding measured by differential scanning calorimetry, circular dichroism, and tryptophan fluorescence reveal that the free energy of unfolding of the T-domain at neutral and mildly acidic pH differ by 3-5 kcal/mol, depending on the experimental conditions. Fluorescence correlation spectroscopy measurements show that the free energy change from the membrane-competent state to the interfacial state is approximately -8 kcal/mol and is pH-independent, while that from the membrane-competent state to the transmembrane state ranges between -9.5 and -12 kcal/mol, depending on the membrane lipid composition and pH. Finally, the thermodynamics of transmembrane insertion of individual helices was tested using an in vitro assay that measures the translocon-assisted integration of test sequences into the microsomal membrane. These experiments suggest that even the most hydrophobic helix TH8 has only a small favorable free energy of insertion. The free energy for the insertion of the consensus insertion unit TH8-TH9 is slightly more favorable, yet less favorable than that measured for the entire protein, suggesting a cooperative effect for the membrane insertion of the helices of the T-domain.
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Affiliation(s)
- Mauricio Vargas-Uribe
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, 66160, USA
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Rosenkranz AA, Ulasov AV, Slastnikova TA, Khramtsov YV, Sobolev AS. Use of intracellular transport processes for targeted drug delivery into a specified cellular compartment. BIOCHEMISTRY (MOSCOW) 2014; 79:928-46. [DOI: 10.1134/s0006297914090090] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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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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Vargas-Uribe M, Rodnin MV, Ladokhin AS. Comparison of membrane insertion pathways of the apoptotic regulator Bcl-xL and the diphtheria toxin translocation domain. Biochemistry 2013; 52:7901-9. [PMID: 24134052 DOI: 10.1021/bi400926k] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The diphtheria toxin translocation domain (T-domain) and the apoptotic repressor Bcl-xL are membrane proteins that adopt their final topology by switching folds from a water-soluble to a membrane-inserted state. While the exact molecular mechanisms of this transition are not clearly understood in either case, the similarity in the structures of soluble states of the T-domain and Bcl-xL led to the suggestion that their membrane insertion pathways will be similar, as well. Previously, we have applied an array of spectroscopic methods to characterize the pH-triggered refolding and membrane insertion of the diphtheria toxin T-domain. Here, we use the same set of methods to describe the membrane insertion pathway of Bcl-xL, which allows us to make a direct comparison between both systems with respect to the thermodynamic stability in solution, pH-dependent membrane association, and transmembrane insertion. Thermal denaturation measured by circular dichroism indicates that, unlike the T-domain, Bcl-xL does not undergo a pH-dependent destabilization of the structure. Förster resonance energy transfer measurements demonstrate that Bcl-xL undergoes reversible membrane association modulated by the presence of anionic lipids, suggesting that formation of the membrane-competent form occurs close to the membrane interface. Membrane insertion of the main hydrophobic helical hairpin of Bcl-xL, α5-α6, was studied by site-selective attachment of environment-sensitive dye NBD. In contrast to the insertion of the corresponding TH8-TH9 hairpin into the T-domain, insertion of α5-α6 was found not to depend strongly on the presence of anionic lipids. Taken together, our results indicate that while Bcl-xL and the T-domain share structural similarities, their modes of conformational switching and membrane insertion pathways are distinctly different.
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Affiliation(s)
- Mauricio Vargas-Uribe
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States
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