Publications by authors named "Mirko Bischofberger"

11 Publications

  • Page 1 of 1

Revealing Assembly of a Pore-Forming Complex Using Single-Cell Kinetic Analysis and Modeling.

Biophys J 2016 Apr;110(7):1574-1581

Center of Synthetic and Systems Biology, University of Edinburgh, Edinburgh, United Kingdom. Electronic address:

Many biological processes depend on the sequential assembly of protein complexes. However, studying the kinetics of such processes by direct methods is often not feasible. As an important class of such protein complexes, pore-forming toxins start their journey as soluble monomeric proteins, and oligomerize into transmembrane complexes to eventually form pores in the target cell membrane. Here, we monitored pore formation kinetics for the well-characterized bacterial pore-forming toxin aerolysin in single cells in real time to determine the lag times leading to the formation of the first functional pores per cell. Probabilistic modeling of these lag times revealed that one slow and seven equally fast rate-limiting reactions best explain the overall pore formation kinetics. The model predicted that monomer activation is the rate-limiting step for the entire pore formation process. We hypothesized that this could be through release of a propeptide and indeed found that peptide removal abolished these steps. This study illustrates how stochasticity in the kinetics of a complex process can be exploited to identify rate-limiting mechanisms underlying multistep biomolecular assembly pathways.
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http://dx.doi.org/10.1016/j.bpj.2016.02.035DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4833779PMC
April 2016

Pathogenic pore-forming proteins: function and host response.

Cell Host Microbe 2012 Sep;12(3):266-75

Ecole Polytechnique Fédérale de Lausanne, Global Health Institute, Station 15, CH-1015 Lausanne, Switzerland.

Organisms from all kingdoms produce pore-forming proteins, with the best-characterized being of bacterial origin. The last decade of research has revealed that the channels formed by these proteins can be very diverse, thus differentially affecting target cell-membrane permeability and consequent cellular outcome. The responses to these toxins are also extremely diverse due to multiple downstream effects of pore-induced changes in ion balance. Determining the secondary effects of pore-forming toxins is essential to understand their contribution to infection.
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http://dx.doi.org/10.1016/j.chom.2012.08.005DOI Listing
September 2012

Pore-forming toxins induce multiple cellular responses promoting survival.

Cell Microbiol 2011 Jul 26;13(7):1026-43. Epub 2011 Apr 26.

Global Health Institute, Ecole Polytechnique Fédérale de Lausanne, Faculty of Life Sciences, Lausanne, Switzerland.

Pore-forming toxins (PFTs) are secreted proteins that contribute to the virulence of a great variety of bacterial pathogens. They inflict one of the more disastrous damages a target cell can be exposed to: disruption of plasma membrane integrity. Since this is an ancient form of attack, which bears similarities to mechanical membrane damage, cells have evolved response pathways to these perturbations. Here, it is reported that PFTs trigger very diverse yet specific response pathways. Many are triggered by the decrease in cytoplasmic potassium, which thus emerges as a central regulator. Upon plasma membrane damage, cells activate signalling pathways aimed at restoring plasma membrane integrity and ion homeostasis. Interestingly these pathways do not require protein synthesis. Cells also trigger signalling cascades that allow them to enter a quiescent-like state, where minimal energy is consumed while waiting for plasma membrane damage to be repaired. More specifically, protein synthesis is arrested, cytosolic constituents are recycled by autophagy and energy is stored in lipid droplets.
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http://dx.doi.org/10.1111/j.1462-5822.2011.01600.xDOI Listing
July 2011

Stabilizing patterning in the Drosophila segment polarity network by selecting models in silico.

Biosystems 2010 Oct 22;102(1):3-10. Epub 2010 Jul 22.

Institut Curie, 26 Rue d'Ulm, Paris F-75248, France.

The segmentation of Drosophila is a prime model to study spatial patterning during embryogenesis. The spatial expression of segment polarity genes results from a complex network of interacting proteins whose expression products are maintained after successful segmentation. This prompted us to investigate the stability and robustness of this process using a dynamical model for the segmentation network based on Boolean states. The model consists of intra-cellular as well as inter-cellular interactions between adjacent cells in one spatial dimension. We quantify the robustness of the dynamical segmentation process by a systematic analysis of mutations. Our starting point consists in a previous Boolean model for Drosophila segmentation. We define mathematically the notion of dynamical robustness and show that the proposed model exhibits limited robustness in gene expression under perturbations. We applied in silico evolution (mutation and selection) and discover two classes of modified gene networks that have a more robust spatial expression pattern. We verified that the enhanced robustness of the two new models is maintained in differential equations models. By comparing the predicted model with experiments on mutated flies, we then discuss the two types of enhanced models. Drosophila patterning can be explained by modelling the underlying network of interacting genes. Here we demonstrate that simple dynamical considerations and in silico evolution can enhance the model to robustly express the expected pattern, helping to elucidate the role of further interactions.
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http://dx.doi.org/10.1016/j.biosystems.2010.07.014DOI Listing
October 2010

How today's scientific culture affects young scientists.

Bioessays 2010 May;32(5):369-71

Swiss Federal Institute of Technology (EPFL), Global Health Institute, Lausanne, Switzerland.

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http://dx.doi.org/10.1002/bies.201000003DOI Listing
May 2010

Endocytosis of the anthrax toxin is mediated by clathrin, actin and unconventional adaptors.

PLoS Pathog 2010 Mar 5;6(3):e1000792. Epub 2010 Mar 5.

Global Health Institute, Ecole Polytechnique Fédérale de Lausanne, Faculty of Life Sciences, Lausanne, Switzerland.

The anthrax toxin is a tripartite toxin, where the two enzymatic subunits require the third subunit, the protective antigen (PA), to interact with cells and be escorted to their cytoplasmic targets. PA binds to cells via one of two receptors, TEM8 and CMG2. Interestingly, the toxin times and triggers its own endocytosis, in particular through the heptamerization of PA. Here we show that PA triggers the ubiquitination of its receptors in a beta-arrestin-dependent manner and that this step is required for clathrin-mediated endocytosis. In addition, we find that endocytosis is dependent on the heterotetrameric adaptor AP-1 but not the more conventional AP-2. Finally, we show that endocytosis of PA is strongly dependent on actin. Unexpectedly, actin was also found to be essential for efficient heptamerization of PA, but only when bound to one of its 2 receptors, TEM8, due to the active organization of TEM8 into actin-dependent domains. Endocytic pathways are highly modular systems. Here we identify some of the key players that allow efficient heptamerization of PA and subsequent ubiquitin-dependent, clathrin-mediated endocytosis of the anthrax toxin.
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http://dx.doi.org/10.1371/journal.ppat.1000792DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2832758PMC
March 2010

Structure and assembly of pore-forming proteins.

Curr Opin Struct Biol 2010 Apr 19;20(2):241-6. Epub 2010 Feb 19.

Ecole Polytechnique Fédérale de Lausanne, Global Health Institute, Station 15, Lausanne, Switzerland.

Pore-forming proteins (PFPs), involved in host-pathogen interactions, are produced as soluble, generally monomeric, proteins. To convert from the soluble to the transmembrane form, PFPs assemble, in the vicinity of the target membrane, into ring-like structures, which expose sufficient hydrophobicity to drive spontaneous bilayer insertion. Recent findings have highlighted two interesting aspects: (1) that pores form via similar overall mechanisms even if originating from vastly different structures and (2) specific folds found in PFPs can be found in widely different organisms, as distant as prokaryotes and mammals, highlighting that pore formation is an ancient form of attack that has been remarkably conserved.
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http://dx.doi.org/10.1016/j.sbi.2010.01.013DOI Listing
April 2010

Membrane injury by pore-forming proteins.

Curr Opin Cell Biol 2009 Aug 11;21(4):589-95. Epub 2009 May 11.

Ecole Polytechnique Fédérale de Lausanne, Global Health Institute, Lausanne, Switzerland.

The plasma membrane defines the boundary of every living cell, and its integrity is essential for life. The plasma membrane may, however, be challenged by mechanical stress or pore-forming proteins produced by the organism itself or invading pathogens. We will here review recent findings about pore-forming proteins from different organisms, highlighting their structural and functional similarities, and describe the mechanisms that lead to membrane repair, since remarkably, cells can repair breaches in their plasma membrane of up to 10,000 microm(2).
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http://dx.doi.org/10.1016/j.ceb.2009.04.003DOI Listing
August 2009

A self-regulatory system of interlinked signaling feedback loops controls mouse limb patterning.

Science 2009 Feb;323(5917):1050-3

Developmental Genetics, Department of Biomedicine, University of Basel, Mattenstrasse 28, CH-4058 Basel, Switzerland.

Embryogenesis depends on self-regulatory interactions between spatially separated signaling centers, but few of these are well understood. Limb development is regulated by epithelial-mesenchymal (e-m) feedback loops between sonic hedgehog (SHH) and fibroblast growth factor (FGF) signaling involving the bone morphogenetic protein (BMP) antagonist Gremlin1 (GREM1). By combining mouse molecular genetics with mathematical modeling, we showed that BMP4 first initiates and SHH then propagates e-m feedback signaling through differential transcriptional regulation of Grem1 to control digit specification. This switch occurs by linking a fast BMP4/GREM1 module to the slower SHH/GREM1/FGF e-m feedback loop. This self-regulatory signaling network results in robust regulation of distal limb development that is able to compensate for variations by interconnectivity among the three signaling pathways.
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http://dx.doi.org/10.1126/science.1168755DOI Listing
February 2009

Exotoxin secretion: getting out to find the way in.

Cell Host Microbe 2008 Jan;3(1):7-8

Global Health Institute, Ecole Polytechnique Fédérale de Lausanne, Station 15, CH 1015 Lausanne, Switzerland.

During infection, most pathogenic bacteria deliver proteins to the host cell cytoplasm to manipulate host behavior. In this issue of Cell Host & Microbe, Spanò and colleagues describe a system where a bacterium produces an exotoxin while inside the host cell. Only after this exotoxin is transported to the mammalian cell surface and secreted into the extracellular milieu can it intoxicate the infected cell or noninfected distant cells.
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http://dx.doi.org/10.1016/j.chom.2007.12.003DOI Listing
January 2008

The nodal precursor acting via activin receptors induces mesoderm by maintaining a source of its convertases and BMP4.

Dev Cell 2006 Sep;11(3):313-23

Ecole Polytechnique Fédérale de Lausanne EPFL-ISREC, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.

During early mouse development, the subtilisin-like proprotein convertases (SPC) Furin and PACE4 pattern the primitive ectoderm and visceral endoderm, presumably by activating the TGFss-related Nodal precursor. Here, mutation of the SPC motif provides direct evidence that Nodal processing is essential to specify anterior visceral endoderm and mesendoderm. Surprisingly, however, the Nodal precursor binds and activates activin receptors to maintain expression of Furin, PACE4, and Bmp4 in extraembryonic ectoderm at a distance from the Nodal source. In return, Bmp4 induces Wnt3, which amplifies Nodal expression in the epiblast and mediates induction of mesoderm. We conclude that uncleaved Nodal sustains the extraembryonic source of proprotein convertases and Bmp4 to amplify Nodal signaling in two nonredundant feedback loops with dual timescales and to localize primitive streak formation at the posterior pole. Based on mathematical modeling, we discuss how these sequential loops control cell fate.
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http://dx.doi.org/10.1016/j.devcel.2006.07.005DOI Listing
September 2006