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Toke O. Structural and Dynamic Determinants of Molecular Recognition in Bile Acid-Binding Proteins. Int J Mol Sci 2022; 23:ijms23010505. [PMID: 35008930 PMCID: PMC8745080 DOI: 10.3390/ijms23010505] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/30/2021] [Accepted: 12/31/2021] [Indexed: 12/12/2022] Open
Abstract
Disorders in bile acid transport and metabolism have been related to a number of metabolic disease states, atherosclerosis, type-II diabetes, and cancer. Bile acid-binding proteins (BABPs), a subfamily of intracellular lipid-binding proteins (iLBPs), have a key role in the cellular trafficking and metabolic targeting of bile salts. Within the family of iLBPs, BABPs exhibit unique binding properties including positive binding cooperativity and site-selectivity, which in different tissues and organisms appears to be tailored to the local bile salt pool. Structural and biophysical studies of the past two decades have shed light on the mechanism of bile salt binding at the atomic level, providing us with a mechanistic picture of ligand entry and release, and the communication between the binding sites. In this review, we discuss the emerging view of bile salt recognition in intestinal- and liver-BABPs, with examples from both mammalian and non-mammalian species. The structural and dynamic determinants of the BABP-bile–salt interaction reviewed herein set the basis for the design and development of drug candidates targeting the transcellular traffic of bile salts in enterocytes and hepatocytes.
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Affiliation(s)
- Orsolya Toke
- Laboratory for NMR Spectroscopy, Structural Research Centre, Research Centre for Natural Sciences, 2 Magyar Tudósok Körútja, H-1117 Budapest, Hungary
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2
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Sosa Morales MC, Juárez AC, Montich GG, Álvarez RMS. Interaction of the antibiotic peptide nisin with anionic membranes in different phase-states: a vibrational study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019; 215:389-397. [PMID: 30856583 DOI: 10.1016/j.saa.2019.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 02/20/2019] [Accepted: 03/04/2019] [Indexed: 06/09/2023]
Abstract
Interactions between the antibiotic peptide nisin and multilamellar vesicles of phosphoglycerol lipids in different phase-states were studied using vibrational spectroscopy. The infrared amide I' band of nisin, both in solution and in the membrane-bound state, was analyzed in the temperature range comprised between 20 and 60 °C in order to study its conformational behavior. Nisin presented mainly unordered and β-turns conformations. Their relative populations varied according to the environment and as the temperature increased: β turns were more favored in the membrane-bound state than in solution, but at higher temperatures the disordered conformation was dominant in both states. Spectral changes of specific infrared bands belonging to the hydrocarbon and polar moieties of lipids were also analyzed to evaluate the perturbation of the lipid membrane order. Nisin interactions with the membrane polar region induced a high restriction to water incorporation, promoting a small increase in the temperature of the lipid phase transition. Raman spectra of nisin/phosphoglycerol systems at ambient temperature were also analyzed. They revealed that the peptide incorporation to a membrane in the fluid phase caused drastic structural modifications in the hydrophobic region of the bilayer. Although nisin may be able to disrupt the hydrophobic portion of the bilayer in the gel phase, the most of the peptide molecule remained at the membrane surface interacting with the polar headgroups. This work provides evidence of a differential effect of nisin on anionic membranes, depending on the phase-state of the lipid.
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Affiliation(s)
- Marcelo C Sosa Morales
- Instituto de Química del Noroeste Argentino (INQUINOA), Universidad Nacional de Tucumán, CONICET, San Miguel de Tucumán, Argentina
| | - Ana C Juárez
- Instituto de Química del Noroeste Argentino (INQUINOA), Universidad Nacional de Tucumán, CONICET, San Miguel de Tucumán, Argentina
| | - Guillermo G Montich
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Rosa M S Álvarez
- Instituto de Química del Noroeste Argentino (INQUINOA), Universidad Nacional de Tucumán, CONICET, San Miguel de Tucumán, Argentina.
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Thermal unfolding of calreticulin. Structural and thermodynamic characterization of the transition. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:175-183. [DOI: 10.1016/j.bbapap.2018.12.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 12/07/2018] [Accepted: 12/10/2018] [Indexed: 12/11/2022]
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Flores SS, Nolan V, Perillo MA, Sánchez JM. Superactive β-galactosidase inclusion bodies. Colloids Surf B Biointerfaces 2018; 173:769-775. [PMID: 30384274 DOI: 10.1016/j.colsurfb.2018.10.049] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 09/23/2018] [Accepted: 10/17/2018] [Indexed: 12/14/2022]
Abstract
Bacterial inclusion bodies (IBs) were historically considered one of the major obstacles in protein production through recombinant DNA techniques and conceived as amorphous deposits formed by passive and rather unspecific structures of unfolded proteins aggregates. Subsequent studies demonstrated that IBs contained an important quantity of active protein. In this work, we proved that recombinant β-galactosidase inclusion bodies (IBβ-Gal) are functional aggregates. Moreover, they exhibit particular features distinct to the soluble version of the enzyme. The particulate enzyme was highly active against lactose in physiological and in acid pH and also retained its activity upon a pre-incubation at high temperature. IBβ-Gal washing or dilution induced the spontaneous release of active enzymes from the supramolecular aggregates. Along this process, we observed a continuous change in the values of several kinetic parameters, including specific activity and Michaelis-Menten constant, measured in the IBβ-Gal suspensions. Simultaneously, IBβ-Gal turned into a more heterogeneous population where smaller particles appeared. The released protein exhibited secondary structure features more similar to those of the soluble species than to the aggregated enzyme. Concluding, IBβ-Gal represents a reservoir and packed source of highly active and stable enzyme.
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Affiliation(s)
- Sandra S Flores
- Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, ICTA and Departamento de Química, Cátedra de Química Biológica, Córdoba, Argentina; CONICET, Instituto de Investigaciones Biológicas y Tecnológicas (IIBYT), Córdoba, Argentina
| | - Verónica Nolan
- Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, ICTA and Departamento de Química, Cátedra de Química Biológica, Córdoba, Argentina; CONICET, Instituto de Investigaciones Biológicas y Tecnológicas (IIBYT), Córdoba, Argentina
| | - María A Perillo
- Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, ICTA and Departamento de Química, Cátedra de Química Biológica, Córdoba, Argentina; CONICET, Instituto de Investigaciones Biológicas y Tecnológicas (IIBYT), Córdoba, Argentina
| | - Julieta M Sánchez
- Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, ICTA and Departamento de Química, Cátedra de Química Biológica, Córdoba, Argentina; CONICET, Instituto de Investigaciones Biológicas y Tecnológicas (IIBYT), Córdoba, Argentina.
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Laulumaa S, Nieminen T, Raasakka A, Krokengen OC, Safaryan A, Hallin EI, Brysbaert G, Lensink MF, Ruskamo S, Vattulainen I, Kursula P. Structure and dynamics of a human myelin protein P2 portal region mutant indicate opening of the β barrel in fatty acid binding proteins. BMC STRUCTURAL BIOLOGY 2018; 18:8. [PMID: 29940944 PMCID: PMC6020228 DOI: 10.1186/s12900-018-0087-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Accepted: 06/13/2018] [Indexed: 02/04/2023]
Abstract
Background Myelin is a multilayered proteolipid sheath wrapped around selected axons in the nervous system. Its constituent proteins play major roles in forming of the highly regular membrane structure. P2 is a myelin-specific protein of the fatty acid binding protein (FABP) superfamily, which is able to stack lipid bilayers together, and it is a target for mutations in the human inherited neuropathy Charcot-Marie-Tooth disease. A conserved residue that has been proposed to participate in membrane and fatty acid binding and conformational changes in FABPs is Phe57. This residue is thought to be a gatekeeper for the opening of the portal region upon ligand entry and egress. Results We performed a structural characterization of the F57A mutant of human P2. The mutant protein was crystallized in three crystal forms, all of which showed changes in the portal region and helix α2. In addition, the behaviour of the mutant protein upon lipid bilayer binding suggested more unfolding than previously observed for wild-type P2. On the other hand, membrane binding rendered F57A heat-stable, similarly to wild-type P2. Atomistic molecular dynamics simulations showed opening of the side of the discontinuous β barrel, giving important indications on the mechanism of portal region opening and ligand entry into FABPs. The results suggest a central role for Phe57 in regulating the opening of the portal region in human P2 and other FABPs, and the F57A mutation disturbs dynamic cross-correlation networks in the portal region of P2. Conclusions Overall, the F57A variant presents similar properties to the P2 patient mutations recently linked to Charcot-Marie-Tooth disease. Our results identify Phe57 as a residue regulating conformational changes that may accompany membrane surface binding and ligand exchange in P2 and other FABPs. Electronic supplementary material The online version of this article (10.1186/s12900-018-0087-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Saara Laulumaa
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland.,European Spallation Source (ESS), Lund, Sweden
| | - Tuomo Nieminen
- Department of Physics, Tampere University of Technology, Tampere, Finland
| | - Arne Raasakka
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Oda C Krokengen
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | | | - Erik I Hallin
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Guillaume Brysbaert
- Unité de Glycobiologie Structurale et Fonctionnelle, University of Lille, CNRS UMR8576 UGSF, F-59000, Lille, France
| | - Marc F Lensink
- Unité de Glycobiologie Structurale et Fonctionnelle, University of Lille, CNRS UMR8576 UGSF, F-59000, Lille, France
| | - Salla Ruskamo
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland
| | - Ilpo Vattulainen
- Department of Physics, Tampere University of Technology, Tampere, Finland.,Department of Physics, University of Helsinki, Helsinki, Finland
| | - Petri Kursula
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland. .,Department of Biomedicine, University of Bergen, Bergen, Norway.
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Galassi VV, Villarreal MA, Montich GG. Relevance of the protein macrodipole in the membrane-binding process. Interactions of fatty-acid binding proteins with cationic lipid membranes. PLoS One 2018. [PMID: 29518146 PMCID: PMC5843346 DOI: 10.1371/journal.pone.0194154] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The fatty acid-binding proteins L-BABP and Rep1-NCXSQ bind to anionic lipid membranes by electrostatic interactions. According to Molecular Dynamics (MD) simulations, the interaction of the protein macrodipole with the membrane electric field is a driving force for protein binding and orientation in the interface. To further explore this hypothesis, we studied the interactions of these proteins with cationic lipid membranes. As in the case of anionic lipid membranes, we found that both proteins, carrying a negative as well as a positive net charge, were bound to the positively charged membrane. Their major axis, those connecting the bottom of the β-barrel with the α-helix portal domain, were rotated about 180 degrees as compared with their orientations in the anionic lipid membranes. Fourier transform infrared (FTIR) spectroscopy of the proteins showed that the positively charged membranes were also able to induce conformational changes with a reduction of the β-strand proportion and an increase in α-helix secondary structure. Fatty acid-binding proteins (FABPs) are involved in several cell processes, such as maintaining lipid homeostasis in cells. They transport hydrophobic molecules in aqueous medium and deliver them into lipid membranes. Therefore, the interfacial orientation and conformation, both shown herein to be electrostatically determined, have a strong correlation with the specific mechanism by which each particular FABP exerts its biological function.
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Affiliation(s)
- Vanesa V. Galassi
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica “Ranwel Caputto”, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina
| | - Marcos A. Villarreal
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Teórica y Computacional, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba. Instituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC), Córdoba, Argentina
| | - Guillermo G. Montich
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica “Ranwel Caputto”, Córdoba, Argentina
- CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina
- * E-mail:
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7
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Conformational changes, from β-strand to α-helix, of the fatty acid-binding protein ReP1-NCXSQ in anionic lipid membranes: dependence with the vesicle curvature. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2017; 47:165-177. [DOI: 10.1007/s00249-017-1243-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 05/31/2017] [Accepted: 07/10/2017] [Indexed: 10/19/2022]
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8
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D'Onofrio M, Zanzoni S, Munari F, Monaco HL, Assfalg M, Capaldi S. The long variant of human ileal bile acid-binding protein associated with colorectal cancer exhibits sub-cellular localization and lipid binding behaviour distinct from those of the common isoform. Biochim Biophys Acta Gen Subj 2017; 1861:2315-2324. [PMID: 28689989 DOI: 10.1016/j.bbagen.2017.07.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Revised: 06/09/2017] [Accepted: 07/05/2017] [Indexed: 12/29/2022]
Abstract
BACKGROUND Ileal bile acid-binding protein, IBABP, participates in the intracellular trafficking of bile salts and influences their signaling activities. The recently discovered variant, IBABP-L, bearing an N-terminal 49-amino acid extension, was found to be associated with colorectal cancer and to protect cancer cells from the cytotoxic effects of deoxycholate. However, the precise function and the molecular properties of this variant are currently unknown. METHODS Bioinformatics tools and confocal microscopy were used to investigate the sub-cellular localization of IBABP-L; protein dynamics, ligand binding and interaction with membrane models were studied by 2D NMR and fluorescence spectroscopy. RESULTS Based on sub-cellular localization experiments we conclude that IBABP-L is targeted to the secretory pathway by a 24-residue signal peptide and, upon its cleavage, the mature protein is constitutively released into the extracellular space. Site-resolved NMR experiments indicated the distinct preference of primary and secondary bile salts to form either heterotypic or homotypic complexes with IBABP-L. The presence of the relatively dynamic N-terminal extension, originating only subtle conformational perturbations in the globular domain, was found to influence binding site occupation in IBABP-L as compared to IBABP. Even more pronounced differences were found in the tendency of the two variants to associate with phospholipid bilayers. CONCLUSIONS IBABP-L exhibits different sub-cellular localization, ligand-binding properties and membrane interaction propensity compared to the canonical short isoform. GENERAL SIGNIFICANCE Our results constitute an essential first step towards an understanding of the role of IBABP-L in bile salt trafficking and signaling under healthy and pathological conditions.
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Affiliation(s)
- Mariapina D'Onofrio
- Biomolecular NMR Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy
| | - Serena Zanzoni
- Biomolecular NMR Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy
| | - Francesca Munari
- Biomolecular NMR Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy
| | - Hugo L Monaco
- Biocrystallography Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy
| | - Michael Assfalg
- Biomolecular NMR Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy.
| | - Stefano Capaldi
- Biocrystallography Laboratory, Department of Biotechnology, University of Verona, Ca' Vignal 1, Strada Le Grazie 15, 37134 Verona, Italy.
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Sayegh RSR, Batista IDFC, de Melo RL, Riske KA, Daffre S, Montich G, da Silva Junior PI. Longipin: An Amyloid Antimicrobial Peptide from the Harvestman Acutisoma longipes (Arachnida: Opiliones) with Preferential Affinity for Anionic Vesicles. PLoS One 2016; 11:e0167953. [PMID: 27997568 PMCID: PMC5172563 DOI: 10.1371/journal.pone.0167953] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 11/22/2016] [Indexed: 12/24/2022] Open
Abstract
In contrast to vertebrate immune systems, invertebrates lack an adaptive response and rely solely on innate immunity in which antimicrobial peptides (AMPs) play an essential role. Most of them are membrane active molecules that are typically unstructured in solution and adopt secondary/tertiary structures upon binding to phospholipid bilayers. This work presents the first characterization of a constitutive AMP from the hemolymph of an Opiliones order animal: the harvestman Acutisoma longipes. This peptide was named longipin. It presents 18 aminoacid residues (SGYLPGKEYVYKYKGKVF) and a positive net charge at neutral pH. No similarity with other AMPs was observed. However, high sequence similarity with heme-lipoproteins from ticks suggested that longipin might be a protein fragment. The synthetic peptide showed enhanced antifungal activity against Candida guilliermondii and C. tropicalis yeasts (MIC: 3.8–7.5 μM) and did not interfered with VERO cells line viability at all concentrations tested (200–0.1 μM). This selectivity against microbial cells is related to the highest affinity of longipin for anionic charged vesicles (POPG:POPC) compared to zwitterionic ones (POPC), once microbial plasma membrane are generally more negatively charged compared to mammalian cells membrane. Dye leakage from carboxyfluorescein-loaded POPG:POPC vesicles suggested that longipin is a membrane active antimicrobial peptide and FT-IR spectroscopy showed that the peptide chain is mainly unstructured in solution or in the presence of POPC vesicles. However, upon binding to POPG:POPC vesicles, the FT-IR spectrum showed bands related to β-sheet and amyloid-like fibril conformations in agreement with thioflavin-T binding assays, indicating that longipin is an amyloid antimicrobial peptide.
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Affiliation(s)
- Raphael Santa Rosa Sayegh
- Programa Interunidades em Biotecnologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
- Laboratório Especial de Toxinologia Aplicada, Instituto Butantan, São Paulo, Brazil
- * E-mail: (RSSS); (PISJ)
| | - Isabel de Fátima Correia Batista
- Unidade de Sequenciamento de Proteínas e Peptídeos, Instituto Butantan, São Paulo, Brazil
- Laboratório de Bioquímica e Biofísica, Instituto Butantan, São Paulo, Brazil
| | - Robson Lopes de Melo
- Laboratório Especial de Toxinologia Aplicada, Instituto Butantan, São Paulo, Brazil
| | - Karin A. Riske
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Sirlei Daffre
- Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Guillermo Montich
- Centro de Investigaciones en Quimica Biológica de Córdoba (CIQUIBIC, UNC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Pedro Ismael da Silva Junior
- Programa Interunidades em Biotecnologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
- Laboratório Especial de Toxinologia Aplicada, Instituto Butantan, São Paulo, Brazil
- * E-mail: (RSSS); (PISJ)
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PEG-induced molecular crowding leads to a relaxed conformation, higher thermal stability and lower catalytic efficiency of Escherichia coli β-galactosidase. Colloids Surf B Biointerfaces 2015; 136:1202-6. [DOI: 10.1016/j.colsurfb.2015.11.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 10/30/2015] [Accepted: 11/02/2015] [Indexed: 11/21/2022]
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11
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Galassi VV, Villarreal MA, Posada V, Montich GG. Interactions of the fatty acid-binding protein ReP1-NCXSQ with lipid membranes. Influence of the membrane electric field on binding and orientation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:910-20. [DOI: 10.1016/j.bbamem.2013.11.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Revised: 11/12/2013] [Accepted: 11/13/2013] [Indexed: 11/17/2022]
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12
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Ceccon A, D'Onofrio M, Zanzoni S, Longo DL, Aime S, Molinari H, Assfalg M. NMR investigation of the equilibrium partitioning of a water-soluble bile salt protein carrier to phospholipid vesicles. Proteins 2013; 81:1776-91. [DOI: 10.1002/prot.24329] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2013] [Revised: 04/29/2013] [Accepted: 05/09/2013] [Indexed: 11/07/2022]
Affiliation(s)
- Alberto Ceccon
- Department of Biotechnology; University of Verona; 37134 Verona Italy
| | | | - Serena Zanzoni
- Department of Biotechnology; University of Verona; 37134 Verona Italy
| | - Dario Livio Longo
- Department of Molecular Biotechnologies and Health Sciences; Molecular Imaging Center, University of Torino; 10126 Torino Italy
| | - Silvio Aime
- Department of Molecular Biotechnologies and Health Sciences; Molecular Imaging Center, University of Torino; 10126 Torino Italy
| | | | - Michael Assfalg
- Department of Biotechnology; University of Verona; 37134 Verona Italy
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Sánchez JM, Nolan V, Perillo MA. β-Galactosidase at the membrane–water interface: A case of an active enzyme with non-native conformation. Colloids Surf B Biointerfaces 2013; 108:1-7. [DOI: 10.1016/j.colsurfb.2013.02.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 02/06/2013] [Accepted: 02/07/2013] [Indexed: 12/01/2022]
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14
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Ambroggio EE, Fidelio GD. Lipid-like behavior of signal sequence peptides at air–water interface. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:708-14. [DOI: 10.1016/j.bbamem.2012.11.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Revised: 10/18/2012] [Accepted: 11/05/2012] [Indexed: 11/28/2022]
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15
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Berberián G, Podjarny A, DiPolo R, Beaugé L. Metabolic regulation of the squid nerve Na⁺/Ca²⁺ exchanger: recent kinetic, biochemical and structural developments. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 108:47-63. [PMID: 21964458 DOI: 10.1016/j.pbiomolbio.2011.09.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 08/30/2011] [Accepted: 09/13/2011] [Indexed: 11/25/2022]
Abstract
The Na⁺/Ca²⁺ exchangers are structural membrane proteins, essential for the extrusion of Ca²⁺ from most animal cells. Apart from the transport sites, they have several interacting ionic and metabolic sites located at the intracellular loop of the exchanger protein. One of these, the intracellular Ca²⁺ regulatory sites, are essential and must be occupied by Ca²⁺ to allow any type of ion (Na⁺ or Ca²⁺) translocation. Intracellular protons and Na⁺ are inhibitory by reducing the affinity of the regulatory sites for Ca²⁺; MgATP stimulates by antagonizing H⁺ and Na⁺. We have proposed a kinetic scheme to explain all ionic and metabolic regulation of the squid nerve Na⁺/Ca²⁺ exchanger. This model uniquely accounts for most of the new kinetic data provided here; however, none of the existing models can explain the trans effects of the Ca(i)²⁺-regulatory sites on external cation transport sites; i.e. all models are incomplete. MgATP up-regulation of the squid Na⁺/Ca²⁺ exchanger requires a cytosolic protein, which has been recently identified as a member of the lipocalin super family of Lipid Binding Proteins (LBP or FABP) of 132 amino acids (ReP1-NCXSQ, access to GenBank EU981897). This protein was cloned, expressed and purified. To be active, ReP1-NCXSQ must be phosphorylated from MgATP by a kinase present in the plasma membrane. Phosphorylated ReP1-NCXSQ can stimulate the exchanger in the absence of ATP. Experiments with proteoliposomes proved that this up-regulation can take place just with the lipid membrane and the exchanger protein. The structure of ReP1-NCXSQ predicted from the amino acid sequence has been confirmed by X-ray crystal analysis; it has a "barrel" formed by ten beta sheets and two alpha helices, with a lipid coordinated by hydrogen bonds with Arg 126 and Tyr 128.
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Affiliation(s)
- Graciela Berberián
- Laboratorio de Biofísica, Instituto de Investigación Médica "Mercedes y Martín Ferreyra" (INIMEC-CONICET), Casilla de Correo 389, 5000 Córdoba, Argentina
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16
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Decca MB, Galassi VV, Perduca M, Monaco HL, Montich GG. Influence of the Lipid Phase State and Electrostatic Surface Potential on the Conformations of a Peripherally Bound Membrane Protein. J Phys Chem B 2010; 114:15141-50. [DOI: 10.1021/jp104035z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- María B. Decca
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC−CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina, and Laboratorio di Biocrystallografia, Dipartimento Scientifico e Tecnologico, Università di Verona, Italia
| | - Vanesa V. Galassi
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC−CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina, and Laboratorio di Biocrystallografia, Dipartimento Scientifico e Tecnologico, Università di Verona, Italia
| | - Massimiliano Perduca
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC−CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina, and Laboratorio di Biocrystallografia, Dipartimento Scientifico e Tecnologico, Università di Verona, Italia
| | - Hugo L. Monaco
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC−CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina, and Laboratorio di Biocrystallografia, Dipartimento Scientifico e Tecnologico, Università di Verona, Italia
| | - Guillermo G. Montich
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC−CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina, and Laboratorio di Biocrystallografia, Dipartimento Scientifico e Tecnologico, Università di Verona, Italia
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17
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Abstract
The liver bile acid-binding proteins, L-BABPs, formerly called the liver "basic" fatty acid-binding proteins, are a subfamily of the fatty acid-binding proteins, FABPs. All the members of this protein group share the same fold: a 10 stranded beta barrel in which two short helices are inserted in between the first and the second strand of antiparallel beta sheet. The barrel encloses the ligand binding cavity of the protein while the two helices are believed to be involved in ligand accessibility to the binding site. The L-BABP subfamily has been found to be present in the liver of several vertebrates: fish, amphibians, reptiles, and birds but not in mammals. The members of the FABP family present in mammals that appear to be more closely related to the L-BABPs are the liver FABPs and the ileal BABPs, both very extensively studied. Several L-BABP X-ray structures are available and chicken L-BABP has also been studied using NMR spectroscopy. The stoichiometry of ligand binding for bile acids, first determined by X-ray crystallography for the chicken liver protein, is of two cholates per protein molecule with the only exception of zebrafish L-BABP which, due to the presence of a disulfide bridge, has a stoichiometry of 1:1. The stoichiometry of ligand binding for fatty acids, determined with several different techniques, is 1:1. An unanswered question of great relevance is the identity of the protein that in mammals performs the function that in other vertebrates is carried out by the L-BABPS.
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Affiliation(s)
- Hugo L Monaco
- Department of Biotechnology, University of Verona, Strada Le Grazie 15, Verona 37134, Italy.
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18
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Pedò M, Löhr F, D'Onofrio M, Assfalg M, Dötsch V, Molinari H. NMR studies reveal the role of biomembranes in modulating ligand binding and release by intracellular bile acid binding proteins. J Mol Biol 2009; 394:852-63. [PMID: 19836400 DOI: 10.1016/j.jmb.2009.10.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Revised: 10/05/2009] [Accepted: 10/08/2009] [Indexed: 10/20/2022]
Abstract
Bile acid molecules are transferred vectorially between basolateral and apical membranes of hepatocytes and enterocytes in the context of the enterohepatic circulation, a process regulating whole body lipid homeostasis. This work addresses the role of the cytosolic lipid binding proteins in the intracellular transfer of bile acids between different membrane compartments. We present nuclear magnetic resonance (NMR) data describing the ternary system composed of the bile acid binding protein, bile acids, and membrane mimetic systems, such as anionic liposomes. This work provides evidence that the investigated liver bile acid binding protein undergoes association with the anionic membrane and binding-induced partial unfolding. The addition of the physiological ligand to the protein-liposome mixture is capable of modulating this interaction, shifting the equilibrium towards the free folded holo protein. An ensemble of NMR titration experiments, based on nitrogen-15 protein and ligand observation, confirm that the membrane and the ligand establish competing binding equilibria, modulating the cytoplasmic permeability of bile acids. These results support a mechanism of ligand binding and release controlled by the onset of a bile salt concentration gradient within the polarized cell. The location of a specific protein region interacting with liposomes is highlighted.
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Affiliation(s)
- Massimo Pedò
- Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy
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19
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Kinetics of lipid-membrane binding and conformational change of L-BABP. Biochem Biophys Res Commun 2009; 382:771-5. [DOI: 10.1016/j.bbrc.2009.03.103] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Accepted: 03/19/2009] [Indexed: 11/23/2022]
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20
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Berberián G, Bollo M, Montich G, Roberts G, Degiorgis JA, Dipolo R, Beaugé L. A novel lipid binding protein is a factor required for MgATP stimulation of the squid nerve Na+/Ca2+ exchanger. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1255-62. [PMID: 19168028 DOI: 10.1016/j.bbamem.2008.12.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2008] [Revised: 12/23/2008] [Accepted: 12/29/2008] [Indexed: 11/26/2022]
Abstract
Here we identify a cytosolic factor essential for MgATP up-regulation of the squid nerve Na(+)/Ca(2+) exchanger. Mass spectroscopy and Western blot analysis established that this factor is a member of the lipocalin super family of lipid binding proteins of 132 amino acids in length. We named it Regulatory protein of the squid nerve sodium calcium exchanger (ReP1-NCXSQ). ReP-1-NCXSQ was cloned, over expressed and purified. Far-UV circular dichroism and infrared spectra suggest a majority of beta-strand in the secondary structure. Moreover, the predicted tertiary structure indicates ten beta-sheets and two short alpha-helices characteristic of most lipid binding proteins. Functional experiments showed that in order to be active ReP1-NCXSQ must become phosphorylated in the presence of MgATP by a kinase that is Staurosporin insensitive. Even more, the phosphorylated ReP1-NCXSQ is able to stimulate the exchanger in the absence of ATP. In addition to the identification of a new member of the lipid binding protein family, this work shows, for the first time, the requirement of a lipid binding protein for metabolic regulation of an ion transporting system.
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Affiliation(s)
- Graciela Berberián
- Laboratorio de Biofísica, Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC-CONICET), Casilla de Correo 389, 5000 Córdoba, Argentina
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21
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Binding and interactions of L-BABP to lipid membranes studied by molecular dynamic simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1390-7. [DOI: 10.1016/j.bbamem.2008.02.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2007] [Revised: 02/26/2008] [Accepted: 02/26/2008] [Indexed: 11/19/2022]
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22
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Basova LV, Tiktopulo EI, Kutyshenko VP, Mauk AG, Bychkova VE. Phospholipid membranes affect tertiary structure of the soluble cytochrome b5 heme-binding domain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1015-26. [PMID: 18275841 DOI: 10.1016/j.bbamem.2007.12.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2007] [Revised: 12/21/2007] [Accepted: 12/28/2007] [Indexed: 11/30/2022]
Abstract
The influence of charged phospholipid membranes on the conformational state of the water-soluble fragment of cytochrome b5 has been investigated by a variety of techniques at neutral pH. The results of this work provide the first evidence that aqueous solutions with high phospholipid/protein molar ratios (pH 7.2) induce the cytochrome to undergo a structural transition from the native conformation to an intermediate state with molten-globule like properties that occur in the presence of an artificial membrane surface and that leads to binding of the protein to the membrane. At other phospholipid/protein ratios, equilibrium was observed between cytochrome free in solution and cytochrome bound to the surface of vesicles. Inhibition of protein binding to the vesicles with increasing ionic strength indicated for the most part an electrostatic contribution to the stability of cytochrome b5-vesicle interactions at pH 7.2. The possible physiological role of membrane-induced conformational change in the structure of cytochrome b5 upon the interaction with its redox partners is discussed.
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Affiliation(s)
- Liana V Basova
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290 Russia
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23
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Decca MB, Perduca M, Monaco HL, Montich GG. Conformational changes of chicken liver bile acid-binding protein bound to anionic lipid membrane are coupled to the lipid phase transitions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1583-91. [PMID: 17466937 DOI: 10.1016/j.bbamem.2007.03.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 03/06/2007] [Accepted: 03/17/2007] [Indexed: 11/28/2022]
Abstract
Chicken liver bile acid-binding protein (L-BABP) binds to anionic lipid membranes by electrostatic interactions and acquires a partly folded state [Nolan, V., Perduca, M., Monaco, H., Maggio, B. and Montich, G. G. (2003) Biochim. Biophys. Acta 1611, 98-106]. We studied the infrared amide I' band of L-BABP bound to dipalmitoylphosphatidylglycerol (DPPG), dimyristoylphosphatidylglycerol (DMPG) and palmitoyloleoylphosphatidylglycerol (POPG) in the range of 7 to 60 degrees C. Besides, the thermotrophic behaviour of DPPG and DMPG was studied in the absence and in the presence of bound-protein by differential scanning calorimetry (DSC) and infrared spectra of the stretching vibration of methylene and carbonyl groups. When L-BABP was bound to lipid membranes in the liquid-crystalline state (POPG between 7 and 30 degrees C) acquired a more unfolded conformation that in membranes in the gel state (DPPG between 7 and 30 degrees C). Nevertheless, this conformational change of the protein in DMPG did not occur at the temperature of the lipid gel to liquid-crystalline phase transition detected by infrared spectroscopy. Instead, the degree of unfolding in the protein was coincident with a phase transition in DMPG that occurs with heat absorption and without change in the lipid order.
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Affiliation(s)
- María Belén Decca
- Centro de Investigaciones en Química Biológica de Córdoba, UNC-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, República Argentina
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24
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Zhang X, Ge N, Keiderling TA. Electrostatic and Hydrophobic Interactions Governing the Interaction and Binding of β-Lactoglobulin to Membranes. Biochemistry 2007; 46:5252-60. [PMID: 17407268 DOI: 10.1021/bi602483p] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The role of electrostatic and hydrophobic interactions in the binding and penetration of beta-lactoglobulin (betaLG) to preformed lipid membranes was studied using various phospholipid micelles and vesicles. Zwitterionic lysophospholipid micelles are able to induce the beta-sheet to alpha-helix transition, as judged by circular dichroism (CD), but the degree of transition is dramatically below and the amount of lipid required above that for anionic phospholipids with equivalent hydrocarbon chains. Anionic phospholipids with short hydrocarbon chains induce only low alpha-helical content in betaLG as compared to phospholipids with the same head group but longer hydrocarbon chains. These results suggest that both electrostatic and hydrophobic interactions are indispensable in betaLG-lipid interaction. Furthermore, air-water interface monolayer surface pressure and fluorescence anisotropy studies reveal that the membrane insertion of betaLG strongly depends on the nature of phospholipids, given the identical headgroup, particularly lipid packing. These results are supported by urea denaturation and acrylamide fluorescence quenching tests and by the FTIR-ATR polarization results for betaLG in multilayers on a surface. Under the same experimental conditions, the membrane binding and insertion of betaLG as well as the stability of the betaLG-lipid complexes can be enhanced by lowering the pH. Collectively, electrostatic interactions play a crucial role in all the processes involved in the betaLG-lipid interaction, while the presence of hydrophobic interaction remains necessary. Finally, betaLG biological function in the transport of fatty acids was tested by demonstrating the release of 2-AS from a 2-AS-betaLG complex on binding to lipids.
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Affiliation(s)
- Xiuqi Zhang
- Department of Chemistry, University of Illinois, 845 West Taylor Street (m/c 111), Chicago, Illinois 60607-7061, USA
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25
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Shepard W, Haouz A, Graña M, Buschiazzo A, Betton JM, Cole ST, Alzari PM. The crystal structure of Rv0813c from Mycobacterium tuberculosis reveals a new family of fatty acid-binding protein-like proteins in bacteria. J Bacteriol 2006; 189:1899-904. [PMID: 17172346 PMCID: PMC1855704 DOI: 10.1128/jb.01435-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The gene Rv0813c from Mycobacterium tuberculosis, which codes for a hypothetical protein of unknown function, is conserved within the order Actinomycetales but absent elsewhere. The crystal structure of Rv0813c reveals a new family of proteins that resemble the fatty acid-binding proteins (FABPs) found in eukaryotes. Rv0813c adopts the 10-stranded beta-barrel fold typical of FABPs but lacks the double-helix insert that covers the entry to the binding site in the eukaryotic proteins. The barrel encloses a deep cavity, at the bottom of which a small cyclic ligand was found to bind to the hydroxyl group of Tyr192. This residue is part of a conserved Arg-X-Tyr motif much like the triad that binds the carboxylate group of fatty acids in FABPs. Most of the residues forming the internal surface of the cavity are conserved in homologous protein sequences found in CG-rich prokaryotes, strongly suggesting that Rv0813c is a member of a new family of bacterial FABP-like proteins that may have roles in the recognition, transport, and/or storage of small molecules in the bacterial cytosol.
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Affiliation(s)
- William Shepard
- Unité de Biochimie Structurale, CNRS URA 2185, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris, France
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26
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Ambroggio EE, Villarreal MA, Montich GG, Rijkers DTS, De Planque MRR, Separovic F, Fidelio GD. Interfacial properties of the M1 segment of the nicotinic acetylcholine receptor. Biophys Chem 2006; 121:171-6. [PMID: 16473457 DOI: 10.1016/j.bpc.2005.12.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2005] [Revised: 12/14/2005] [Accepted: 12/15/2005] [Indexed: 11/30/2022]
Abstract
We have studied the thermodynamic, surface, and structural properties of alphaM1 transmembrane sequence of the nicotinic acetylcholine receptor (nAChR) by using Langmuir monolayer, FT-IR spectroscopy and molecular dynamics simulation techniques in membrane-mimicking environments. M1 spontaneously incorporates into a lipid-free air-water interface, showing a favourable adsorption free energy of -7.2 kcal/mol. A cross-sectional molecular area of 210 A(2)/molecule, a surface potential of 4.2 fV/molecule and a high stability of the film were deducted from pure M1 monolayers. FT-IR experiments and molecular dynamics simulations in membrane-mimicking environments (sodium-dodecyl-sulfate and CCl(4), respectively) indicate coexistence between helical and non-helical structures. Furthermore, mixed peptide-lipid monolayers and monolayer penetration experiments were performed in order to study the peptide-lipid interaction. Mixed with condensed lipids (dipalmitoyl-phosphocholine, and dipalmitoyl-phosphoglycerol), M1 shows immiscible/miscible behaviour at low/high peptide concentration, respectively. Conversely, a complete miscible peptide-lipid interface is observed with liquid-expanded lipids (palmitoyl-oleoyl-phosphocholine, and palmitoyl-oleoyl-phosphoglycerol). Peptide penetration experiments demonstrate that the M1 peptide preferentially interacts with zwitterionic phosphocholine interfaces.
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Affiliation(s)
- Ernesto E Ambroggio
- CIQUIBIC-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Haya de la Torre y Medina Allende, Ciudad Universitaria, Córdoba, Argentina, (CP X5000HUA)
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27
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Ambroggio EE, Separovic F, Bowie JH, Fidelio GD, Bagatolli LA. Direct visualization of membrane leakage induced by the antibiotic peptides: maculatin, citropin, and aurein. Biophys J 2005; 89:1874-81. [PMID: 15994901 PMCID: PMC1366690 DOI: 10.1529/biophysj.105.066589] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Membrane lysis caused by antibiotic peptides is often rationalized by means of two different models: the so-called carpet model and the pore-forming model. We report here on the lytic activity of antibiotic peptides from Australian tree frogs, maculatin 1.1, citropin 1.1, and aurein 1.2, on POPC or POPC/POPG model membranes. Leakage experiments using fluorescence spectroscopy indicated that the peptide/lipid mol ratio necessary to induce 50% of probe leakage was smaller for maculatin compared with aurein or citropin, regardless of lipid membrane composition. To gain further insight into the lytic mechanism of these peptides we performed single vesicle experiments using confocal fluorescence microscopy. In these experiments, the time course of leakage for different molecular weight (water soluble) fluorescent markers incorporated inside of single giant unilamellar vesicles is observed after peptide exposure. We conclude that maculatin and its related peptides demonstrate a pore-forming mechanism (differential leakage of small fluorescent probe compared with high molecular weight markers). Conversely, citropin and aurein provoke a total membrane destabilization with vesicle burst without sequential probe leakage, an effect that can be assigned to a carpeting mechanism of lytic action. Additionally, to study the relevance of the proline residue on the membrane-action properties of maculatin, the same experimental approach was used for maculatin-Ala and maculatin-Gly (Pro-15 was replaced by Ala or Gly, respectively). Although a similar peptide/lipid mol ratio was necessary to induce 50% of leakage for POPC membranes, the lytic activity of maculatin-Ala and maculatin-Gly decreased in POPC/POPG (1:1 mol) membranes compared with that observed for the naturally occurring maculatin sequence. As observed for maculatin, the lytic action of Maculatin-Ala and maculatin-Gly is in keeping with the formation of pore-like structures at the membrane independently of lipid composition.
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Affiliation(s)
- Ernesto E Ambroggio
- CIQUIBIC-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Ciudad Universitaria, Córdoba, Argentina
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