1
|
Marković KG, Grujović MŽ, Koraćević MG, Nikodijević DD, Milutinović MG, Semedo-Lemsaddek T, Djilas MD. Colicins and Microcins Produced by Enterobacteriaceae: Characterization, Mode of Action, and Putative Applications. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:11825. [PMID: 36142096 PMCID: PMC9517006 DOI: 10.3390/ijerph191811825] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 09/12/2022] [Accepted: 09/15/2022] [Indexed: 06/15/2023]
Abstract
Enterobacteriaceae are widely present in many environments related to humans, including the human body and the food that they consume, from both plant or animal origin. Hence, they are considered relevant members of the gastrointestinal tract microbiota. On the other hand, these bacteria are also recognized as putative pathogens, able to impair human health and, in food, they are considered indicators for the microbiological quality and hygiene status of a production process. Nevertheless, beneficial properties have also been associated with Enterobacteriaceae, such as the ability to synthesize peptides and proteins, which can have a role in the structure of microbial communities. Among these antimicrobial molecules, those with higher molecular mass are called colicins, while those with lower molecular mass are named microcins. In recent years, some studies show an emphasis on molecules that can help control the development of pathogens. However, not enough data are available on this subject, especially related to microcins. Hence, this review gathers and summarizes current knowledge on colicins and microcins, potential usage in the treatment of pathogen-associated diseases and cancer, as well as putative applications in food biotechnology.
Collapse
Affiliation(s)
- Katarina G. Marković
- Institute for Information Technologies, Department of Science, University of Kragujevac, Jovana Cvijića bb, 34000 Kragujevac, Serbia
| | - Mirjana Ž. Grujović
- Institute for Information Technologies, Department of Science, University of Kragujevac, Jovana Cvijića bb, 34000 Kragujevac, Serbia
| | - Maja G. Koraćević
- Innovation Center, University of Niš, 18000 Niš, Serbia
- Faculty of Medicine, Department of Pharmacy, University of Niš, 18000 Niš, Serbia
| | - Danijela D. Nikodijević
- Faculty of Science, Department of Biology and Ecology, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac, Serbia
| | - Milena G. Milutinović
- Faculty of Science, Department of Biology and Ecology, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac, Serbia
| | - Teresa Semedo-Lemsaddek
- CIISA—Centro de Investigação Interdisciplinar em Sanidade Animal, Faculdade de Medicina Veterinária, Universidade de Lisboa, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal
- Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), 1300-477 Lisboa, Portugal
| | - Milan D. Djilas
- Institute for Public Health of Vojvodina, Futoška 121, 21000 Novi Sad, Serbia
| |
Collapse
|
2
|
Riedlová K, Dolejšová T, Fišer R, Cwiklik L. H1 helix of colicin U causes phospholipid membrane permeation. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183866. [PMID: 35007517 DOI: 10.1016/j.bbamem.2022.183866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 12/29/2021] [Accepted: 01/03/2022] [Indexed: 06/14/2023]
Abstract
In light of an increasing number of antibiotic-resistant bacterial strains, it is essential to understand an action imposed by various antimicrobial agents on bacteria at the molecular level. One of the leading mechanisms of killing bacteria is related to the alteration of their plasmatic membrane. We study bio-inspired peptides originating from natural antimicrobial proteins colicins, which can disrupt membranes of bacterial cells. Namely, we focus on the α-helix H1 of colicin U, produced by bacterium Shigella boydii, and compare it with analogous peptides derived from two different colicins. To address the behavior of the peptides in biological membranes, we employ a combination of molecular simulations and experiments. We use molecular dynamics simulations to show that all three peptides are stable in model zwitterionic and negatively charged phospholipid membranes. At the molecular level, their embedment leads to the formation of membrane defects, membrane permeation for water, and, for negatively charged lipids, membrane poration. These effects are caused by the presence of polar moieties in the considered peptides. Importantly, simulations demonstrate that even monomeric H1 peptides can form toroidal pores. At the macroscopic level, we employ experimental co-sedimentation and fluorescence leakage assays. We show that the H1 peptide of colicin U incorporates into phospholipid vesicles and disrupts their membranes, causing leakage, in agreement with the molecular simulations. These insights obtained for model systems seem important for understanding the mechanisms of antimicrobial action of natural bacteriocins and for future exploration of small bio-inspired peptides able to disrupt bacterial membranes.
Collapse
Affiliation(s)
- Kamila Riedlová
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic; Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 12800 Prague, Czech Republic
| | - Tereza Dolejšová
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic; Department of Genetics and Microbiology, Faculty of Science, Charles University, Viničná 5, 12843 Prague, Czech Republic
| | - Radovan Fišer
- Department of Genetics and Microbiology, Faculty of Science, Charles University, Viničná 5, 12843 Prague, Czech Republic.
| | - Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic.
| |
Collapse
|
3
|
Abstract
Due to the heterogenous lipid environment in which integral membrane proteins are embedded, they should follow a set of assembly rules, which govern transmembrane protein folding and topogenesis accordingly to a given lipid profile. Recombinant strains of bacteria have been engineered to have different membrane phospholipid compositions by molecular genetic manipulation of endogenous and foreign genes encoding lipid biosynthetic enzymes. Such strains provide a means to investigate the in vivo role of lipids in many different aspects of membrane function, folding and biogenesis. In vitro and in vivo studies established a function of lipids as molecular chaperones and topological determinants specifically assisting folding and topogenesis of membrane proteins. These results led to the extension of the Positive Inside Rule to Charge Balance Rule, which incorporates a role for lipid-protein interactions in determining membrane protein topological organization at the time of initial membrane insertion and dynamically after initial assembly. Membrane protein topogenesis appears to be a thermodynamically driven process in which lipid-protein interactions affect the potency of charged amino acid residues as topological signals. Dual topology for a membrane protein can be established during initial assembly where folding intermediates in multiple topological conformations are in rapid equilibrium (thus separated by a low activation energy), which is determined by the lipid environment. Post-assembly changes in lipid composition or post-translational modifications can trigger a reorganization of protein topology by inducing destabilization and refolding of a membrane protein. The lipid-dependent dynamic nature of membrane protein organization provides a novel means of regulating protein function.
Collapse
|
4
|
Resolving the 3D spatial orientation of helix I in the closed state of the colicin E1 channel domain by FRET. Insights into the integration mechanism. Arch Biochem Biophys 2016; 608:52-73. [DOI: 10.1016/j.abb.2016.08.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 07/27/2016] [Accepted: 08/08/2016] [Indexed: 11/13/2022]
|
5
|
Cosentino K, Ros U, García-Sáez AJ. Assembling the puzzle: Oligomerization of α-pore forming proteins in membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1858:457-466. [PMID: 26375417 DOI: 10.1016/j.bbamem.2015.09.013] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/26/2015] [Accepted: 09/09/2015] [Indexed: 12/21/2022]
Abstract
Pore forming proteins (PFPs) share the ability of creating pores that allow the passage of ions, proteins or other constituents through a wide variety of target membranes, ranging from bacteria to humans. They often cause cell death, as pore formation disrupts the membrane permeability barrier required for maintaining cell homeostasis. The organization into supramolecular complexes or oligomers that pierce the membrane is a common feature of PFPs. However, the molecular pathway of self-assembly and pore opening remains unclear. Here, we review the most recent discoveries in the mechanism of membrane oligomerization and pore formation of a subset of PFPs, the α-PFPs, whose pore-forming domains are formed by helical segments. Only now we are starting to grasp the molecular details of their function, mainly thanks to the introduction of single molecule microscopy and nanoscopy techniques. This article is part of a Special Issue entitled: Pore-forming toxins edited by Mauro Dalla Serra and Franco Gambale.
Collapse
Affiliation(s)
- Katia Cosentino
- Interfaculty Institute of Biochemistry (IFIB), University of Tübingen, Tübingen, Germany.,Max-Planck Institute for Intelligent Systems, Stuttgart, Germany
| | - Uris Ros
- Interfaculty Institute of Biochemistry (IFIB), University of Tübingen, Tübingen, Germany.,Max-Planck Institute for Intelligent Systems, Stuttgart, Germany.,Center for Protein Studies, Havana University, Havana, Cuba
| | - Ana J García-Sáez
- Interfaculty Institute of Biochemistry (IFIB), University of Tübingen, Tübingen, Germany.,Max-Planck Institute for Intelligent Systems, Stuttgart, Germany
| |
Collapse
|
6
|
Slatin SL, Duché D, Baty D. Determinants of the Proton Selectivity of the Colicin A Channel. Biochemistry 2010; 49:4786-93. [DOI: 10.1021/bi100122g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Stephen L. Slatin
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461
| | - Denis Duché
- CNRS, LISM, 31 chemin Joseph Aiguier, 13401 Marseille, France
| | - Daniel Baty
- INSERM, 163 avenue de Luminy, 13288 Marseille, France
| |
Collapse
|
7
|
Ridleya H, Johnson CL, Lakey JH. Interfacial Interactions of Pore-Forming Colicins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 677:81-90. [DOI: 10.1007/978-1-4419-6327-7_7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
|
8
|
Ho D, Merrill AR. Evidence for the Amphipathic Nature and Tilted Topology of Helices 4 and 5 in the Closed State of the Colicin E1 Channel. Biochemistry 2009; 48:1369-80. [DOI: 10.1021/bi801906v] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Derek Ho
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - A. Rod Merrill
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| |
Collapse
|
9
|
Anderluh G, Lakey JH. Disparate proteins use similar architectures to damage membranes. Trends Biochem Sci 2008; 33:482-90. [PMID: 18778941 DOI: 10.1016/j.tibs.2008.07.004] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 06/22/2008] [Accepted: 07/24/2008] [Indexed: 01/30/2023]
Abstract
Membrane disruption can efficiently alter cellular function; indeed, pore-forming toxins (PFTs) are well known as important bacterial virulence factors. However, recent data have revealed that structures similar to those found in PFTs are found in membrane active proteins across disparate phyla. Many similarities can be identified only at the 3D-structural level. Of note, domains found in membrane-attack complex proteins of complement and perforin (MACPF) resemble cholesterol-dependent cytolysins from Gram-positive bacteria, and the Bcl family of apoptosis regulators share similar architectures with Escherichia coli pore-forming colicins. These and other correlations provide considerable help in understanding the structural requirements for membrane binding and pore formation.
Collapse
Affiliation(s)
- Gregor Anderluh
- Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000, Ljubljana, Slovenia.
| | | |
Collapse
|
10
|
Conformation of the Closed Channel State of Colicin A in Proteoliposomes: An Umbrella Model. J Mol Biol 2008; 378:204-14. [DOI: 10.1016/j.jmb.2008.02.038] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2007] [Revised: 02/15/2008] [Accepted: 02/16/2008] [Indexed: 11/18/2022]
|
11
|
Iacovache I, van der Goot FG, Pernot L. Pore formation: an ancient yet complex form of attack. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1611-23. [PMID: 18298943 DOI: 10.1016/j.bbamem.2008.01.026] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2007] [Revised: 01/03/2008] [Accepted: 01/04/2008] [Indexed: 02/07/2023]
Abstract
Bacteria, as well as higher organisms such as sea anemones or earthworms, have developed sophisticated virulence factors such as the pore-forming toxins (PFTs) to mount their attack against the host. One of the most fascinating aspects of PFTs is that they can adopt a water-soluble form at the beginning of their lifetime and become an integral transmembrane protein in the membrane of the target cells. There is a growing understanding of the sequence of events and the various conformational changes undergone by these toxins in order to bind to the host cell surface, to penetrate the cell membranes and to achieve pore formation. These points will be addressed in this review.
Collapse
Affiliation(s)
- Ioan Iacovache
- Global Health Institute, Ecole Polytechnique Fédérale de Lausanne, Faculty of Life Sciences, Station 15, Lausanne, Switzerland
| | | | | |
Collapse
|
12
|
Slatin SL, Finkelstein A, Kienker PK. Anomalous proton selectivity in a large channel: colicin A. Biochemistry 2008; 47:1778-88. [PMID: 18205407 DOI: 10.1021/bi701900x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Some of the bactericidal proteins known as colicins exert their toxic action by forming a large, nonselective channel in the inner membrane of target bacteria. The structure of this channel is unknown. It conducts large ions but has a much smaller conductance than would be expected for a channel of its deduced size. Here we report that the colicin channel, particularly the colicin A channel, is selective for protons over other cations (and anions) by many orders of magnitude. This was deduced from measurements of reversal potentials in pH gradients across planar lipid bilayers containing these channels. For example, in symmetric 0.1 M KCl with a pH 5/pH 8 gradient across the membrane, the reversal potential of colicin A is -21 mV, rather than 0. Such a result would be unremarkable for a narrow channel but is beyond explanation by current understanding of permeation for a channel of its diameter. For this reason, we re-examined the issue of the diameter of the channel lumen and confirmed that the lumen is indeed "too large" ( approximately 10 A) to select for protons by the amount that we measure. We are thus compelled to propose that an unorthodox mechanism is at work in this protein.
Collapse
Affiliation(s)
- Stephen L Slatin
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
| | | | | |
Collapse
|
13
|
Wei Z, White D, Wang J, Musse AA, Merrill AR. Tilted, extended, and lying in wait: the membrane-bound topology of residues Lys-381-Ser-405 of the colicin E1 channel domain. Biochemistry 2007; 46:6074-85. [PMID: 17455912 DOI: 10.1021/bi700317k] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The membrane-bound closed state (zero potential) of the helix 3 segment (Lys-381-Ser-405) of the colicin E1 channel domain was investigated by site-directed fluorescence labeling using a bimane probe tethered to a single cysteine residue of each mutant protein. A number of fluorescence properties of the tethered bimane probe were measured for the soluble channel mutant proteins as well as for the membrane-bound proteins. A new method called helical periodicity surface analysis was employed to fit the fluorescence data to a harmonic wave function using four different statistical methods. The fit of the various data sets to a harmonic wave function indicated that the periodicity of helix 3 in the membrane-bound state is typical for an amphipathic alpha helix (3.7-4.0 residues per turn and an angular frequency between 90 and 97 degrees). Notably, upon membrane binding, helix 3 elongates from 15 residues (soluble structure) to 20 residues by a three- and two-residue extension at the N- and C-termini of the helix, respectively. Dual quencher analysis also revealed that helix 3 is appressed to the surface of the membrane with its N-terminus more deeply buried within the interfacial region of the bilayer than its C-terminus. Finally, contrary to a previous report, our data show that helices 3 and 4 remain separate and independent helices upon membrane association in the absence of a membrane potential.
Collapse
Affiliation(s)
- Zhikui Wei
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
| | | | | | | | | |
Collapse
|
14
|
Cascales E, Buchanan SK, Duché D, Kleanthous C, Lloubès R, Postle K, Riley M, Slatin S, Cavard D. Colicin biology. Microbiol Mol Biol Rev 2007; 71:158-229. [PMID: 17347522 PMCID: PMC1847374 DOI: 10.1128/mmbr.00036-06] [Citation(s) in RCA: 778] [Impact Index Per Article: 45.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Colicins are proteins produced by and toxic for some strains of Escherichia coli. They are produced by strains of E. coli carrying a colicinogenic plasmid that bears the genetic determinants for colicin synthesis, immunity, and release. Insights gained into each fundamental aspect of their biology are presented: their synthesis, which is under SOS regulation; their release into the extracellular medium, which involves the colicin lysis protein; and their uptake mechanisms and modes of action. Colicins are organized into three domains, each one involved in a different step of the process of killing sensitive bacteria. The structures of some colicins are known at the atomic level and are discussed. Colicins exert their lethal action by first binding to specific receptors, which are outer membrane proteins used for the entry of specific nutrients. They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system. The components of each system are known, and their implication in the functioning of the system is described. Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA. The mechanisms of inhibition by specific and cognate immunity proteins are presented. Finally, the use of colicins as laboratory or biotechnological tools and their mode of evolution are discussed.
Collapse
Affiliation(s)
- Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires,Institut de Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, UPR 9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
| | | | | | | | | | | | | | | | | |
Collapse
|
15
|
White D, Musse AA, Wang J, London E, Merrill AR. Toward elucidating the membrane topology of helix two of the colicin E1 channel domain. J Biol Chem 2006; 281:32375-84. [PMID: 16854987 DOI: 10.1074/jbc.m605880200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The membrane-bound closed state of the colicin E1 channel domain was investigated by site-directed fluorescence labeling using a bimane fluorophore attached to each single cysteine residue within helix 2 of each mutant protein. The fluorescence properties of the bimane fluorophore were measured for the membrane-associated form of the closed channel and included fluorescence emission maximum, fluorescence anisotropy, apparent polarity, surface accessibility, and membrane bilayer penetration depth. The fluorescence data show that helix 2 is an amphipathic alpha-helix that is situated parallel to the membrane surface, but it is less deeply embedded within the bilayer interfacial region than is helix 1 in the closed channel. A least squares fit of the various data sets to a harmonic wave function indicated that the periodicity and angular frequency for helix 2 in the membrane-bound state are typical for an amphipathic alpha-helix (3.8 +/- 0.1 residues per turn and 94 +/- 4 degrees, respectively) that is located at an interfacial region of a membrane bilayer. Dual quencher analysis also revealed that helix 2 is peripherally membrane associated, with one face of the helix dipping into the interfacial region of the lipid bilayer and the other face projecting outwardly into the aqueous solvent. Finally, our data show that helices 1 and 2 remain independent helices upon membrane association with a short connector link (Tyr(363)-Gly(364)) and that short amphipathic alpha-helices participate in the formation of a lipid-dependent, toroidal pore for this colicin.
Collapse
Affiliation(s)
- Dawn White
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | | | | | | | | |
Collapse
|
16
|
Musse AA, Wang J, Deleon GP, Prentice GA, London E, Merrill AR. Scanning the Membrane-bound Conformation of Helix 1 in the Colicin E1 Channel Domain by Site-directed Fluorescence Labeling. J Biol Chem 2006; 281:885-95. [PMID: 16299381 DOI: 10.1074/jbc.m511140200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Helix 1 of the membrane-associated closed state of the colicin E1 channel domain was studied by site-directed fluorescence labeling where bimane was covalently attached to a single cysteine residue in each mutant protein. A number of fluorescence properties of the tethered bimane fluorophore were measured in the membrane-bound state of the channel domain, including fluorescence emission maximum, fluorescence quantum yield, fluorescence anisotropy, membrane bilayer penetration depth, surface accessibility, and apparent polarity. The data show that helix 1 is an amphipathic alpha-helix that is situated parallel to the membrane surface. A least squares fit of the various data sets to a harmonic function indicated that the periodicity and angular frequency for helix 1 are typical for an amphipathic alpha-helix (3.7 +/- 0.1 residues per turn and 97 +/- 3.0 degrees, respectively) that is partially bathing into the membrane bilayer. Dual fluorescence quencher analysis also revealed that helix 1 is peripherally membrane-associated, with one face of the helix dipping into the lipid bilayer and the other face projecting toward the solvent. Finally, our data suggest that the helical boundaries of helix 1, at least at the C-terminal region, remain unaffected upon binding to the surface of the membrane in support of a toroidal pore model for this colicin.
Collapse
Affiliation(s)
- Abdiwahab A Musse
- Department of Molecular and Cellular Biology, University of Guelph, Ontario, Canada
| | | | | | | | | | | |
Collapse
|