12756
2015
eng
doctoralthesis
1
2016-02-22
--
2016-02-19
Functional diversification of membrane microdomains in Bacillus subtilis
Funktionale Diversifizierung von Membran-Mikrodomänen in Bacillus subtilis
Eukaryotic cells are considered as evolutionary complex organisms because they possess organelles that enable them to regulate the spatio-temporal organization of cellular processes. Spatio-temporal organization of signal transduction cascades occurs in eukaryotic cells via organization of membrane-associated microdomains or lipid rafts. Lipid rafts are nanoscale-sized domains in the plasma membrane that are constituted by a specific set of lipids and proteins and harbor a number of proteins related to signal transduction and trafficking. The integrity of lipid rafts is important for the assembly and functional coordination of a plethora of signaling networks and associated processes. This integrity is partially mediated by a chaperone protein called flotillin. Disruption of lipid raft integrity, for example via depletion or overproduction of flotillin, alters raft-associated signal transduction cascades and causes severe diseases like Alzheimer’s, Parkinson’s disease or cardiovascular disease.
It was traditionally assumed that a sophisticated compartmentalization of cellular processes like the one exhibited in lipid rafts was exclusive to eukaryotic cells and therefore, lipid rafts have been considered as a hallmark in the evolution of cellular complexity, suggesting that prokaryotic cells were too simple organisms to organize such sophisticated membrane platforms. However, it was recently discovered that bacteria are also able to organize Functional Membrane Microdomains (FMMs) in their cellular membrane that are able to organize and catalyze the functionality of many diverse cellular processes. These FMMs of bacterial membranes contain flotillin-like proteins which play important roles in the organization of FMM-associated cellular processes.
In this dissertation I describe the structural and biological significance of the existence of two distinct flotillin proteins, FloA and FloT, in the FMMs of the bacterial model Bacillus subtilis. Localization studies, proteomic data and transcriptomic analyses show that FloA and FloT are individual scaffold proteins that activate different regulatory programs during bacterial growth. Using the tractable bacterial model system, I show that the functionality of important regulatory proteins, like the protease FtsH or the signaling kinases KinC, PhoR and ResE, is linked to the activity of FMMs and that this is a direct consequence of the scaffold activity of the bacterial flotillins. FloA and FloT distribute heterogeneously along the FMMs of B. subtilis thereby generating a heterogeneous population of FMMs that compartmentalize different signal transduction cascades. Interestingly, diversification of FMMs does not occur randomly, but rather in a controlled spatio-temporal program to ensure the activation of given signaling networks at the right place and time during cell growth.
Eukaryotische Zellen werden als evolutionär komplexe Organismen betrachtet, weil sie Organellen besitzen, mit denen sie die raum-zeitliche Organisation von zellulären Prozessen steuern können. Die räumliche und zeitliche Organisation von Signalwegen in eukaryotischen Zellen erfolgt durch die Abgrenzung von membran-assoziierten Mikrodomänen oder Lipid Rafts. Lipid Rafts sind wenige Nanometer große Felder in der Plasmamembran, die aus einem spezifischen Set von Lipiden und Proteinen zusammengesetzt sind und eine Reihe von für die Signaltransduktion und den Proteintransfer erforderlichen Proteine enthalten. Die Integrität der Lipid Rafts ist wichtig um zahlreiche Signalwege und damit assoziierte Prozesse zu verbinden und funktional zu koordinieren. Diese Integrität wird zum Teil von einem Chaperon-Protein namens Flotillin vermittelt. Eine Beeinträchtigung der Integrität der Lipid Rafts, z.B. aufgrund eines Mangels an Flotillin oder einer Überproduktion von Flotillin, verändert Raft-assoziierte Signalwege und verursacht schwere Erkrankungen wie Alzheimer, Parkinson oder kardiovaskuläre Erkrankungen.
Bislang wurde angenommen, dass eine so anspruchsvolle Kompartimentierung zellulärer Prozesse wie im Falle der Lipid Rafts ausschließlich in eukaryotischen Zellen vorkommt. Lipid Rafts galten daher als Meilenstein in der Evolution der zellulären Komplexität und prokaryotische Zellen als zu einfache Organismen, um solch komplexe Plattformen in der Membran einzurichten. Vor kurzem wurde jedoch herausgefunden, dass Bakterien ebenfalls in der Lage sind, Funktionale Mikrodomänen in der Membran (FMMs) zu formen, die viele verschiedene zelluläre Prozesse organisieren und katalysieren können. Diese FMMs in bakteriellen Membranen enthalten Flotillin-ähnliche Proteine, die wichtige Aufgaben bei der Organisation von FMM-assoziierten Prozessen übernehmen.
In dieser Dissertation beschreibe ich die strukturelle und biologische Signifikanz des Vorkommens der beiden verschiedenen Flotillin-Proteine FloA und FloT in den FMMs des bakteriellen Modellorganismus Bacillus subtilis. Lokalisationsstudien, proteomische Daten und transkriptomische Analysen demonstrieren, dass FloA und FloT individuelle Gerüstproteine sind, die während des Bakterienwachstums verschiedene regulatorische Programme aktivieren. Mit Hilfe des zugänglichen bakteriellen Modellorganismus zeige ich, dass die Funktionsweise von wichtigen regulatorischen Proteinen, wie z.B. der Protease FtsH oder der Signalwegskinasen KinC, PhoR und ResE, an die Aktivität der FMMs gebunden ist, und dass dies eine direkte Folge der stützenden Tätigkeit der bakteriellen Flotilline ist. FloA und FloT sind unterschiedlich in den FMMs von B. subtilis verteilt, wodurch sie eine heterogene Population von FMMs erzeugen, die verschiedene Signalwege abgrenzen kann. Interessanterweise erfolgt die Diversifizierung der FMMs nicht zufällig, sondern durch ein räumlich und zeitlich kontrolliertes Programm, um die Aktivierung von bestimmten Signalwegen am richtigen Ort und zur richtigen Zeit während des Zellwachstums sicherzustellen.
urn:nbn:de:bvb:20-opus-127569
X 126490
Deutsches Urheberrecht mit Print on Demand
Johannes Schneider
deu
swd
Heubacillus
deu
swd
Plasmamembran
deu
swd
Diversifikation <Biologie>
mul
uncontrolled
FMMs
mul
uncontrolled
Bacillus subtilis
mul
uncontrolled
Flotillin
eng
uncontrolled
Lipid Rafts
Biowissenschaften; Biologie
open_access
Graduate School of Life Sciences
Rudolf-Virchow-Zentrum
Universität Würzburg
Universität Würzburg
https://opus.bibliothek.uni-wuerzburg.de/files/12756/Dissertation_Schneider_Johannes_FMMs.pdf
12557
2015
eng
e1005140
4
11
article
1
2016-01-26
--
--
Spatio-temporal Remodeling of Functional Membrane Microdomains Organizes the Signaling Networks of a Bacterium
Lipid rafts are membrane microdomains specialized in the regulation of numerous cellular processes related to membrane organization, as diverse as signal transduction, protein sorting, membrane trafficking or pathogen invasion. It has been proposed that this functional diversity would require a heterogeneous population of raft domains with varying compositions. However, a mechanism for such diversification is not known. We recently discovered that bacterial membranes organize their signal transduction pathways in functional membrane microdomains (FMMs) that are structurally and functionally similar to the eukaryotic lipid rafts. In this report, we took advantage of the tractability of the prokaryotic model Bacillus subtilis to provide evidence for the coexistence of two distinct families of FMMs in bacterial membranes, displaying a distinctive distribution of proteins specialized in different biological processes. One family of microdomains harbors the scaffolding flotillin protein FloA that selectively tethers proteins specialized in regulating cell envelope turnover and primary metabolism. A second population of microdomains containing the two scaffolding flotillins, FloA and FloT, arises exclusively at later stages of cell growth and specializes in adaptation of cells to stationary phase. Importantly, the diversification of membrane microdomains does not occur arbitrarily. We discovered that bacterial cells control the spatio-temporal remodeling of microdomains by restricting the activation of FloT expression to stationary phase. This regulation ensures a sequential assembly of functionally specialized membrane microdomains to strategically organize signaling networks at the right time during the lifespan of a bacterium.
PLoS Genetics
10.1371/journal.pgen.1005140
urn:nbn:de:bvb:20-opus-125577
PLoS Genetics 11(4): e1005140. doi:10.1371/journal.pgen.1005140
335568
Johannes Schneider
Teresa Klein
Benjamin Mielich-Süss
Gudrun Koch
Christian Franke
Oskar P. Kuipers
Ákos T. Kovács
Markus Sauer
Daniel Lopez
eng
uncontrolled
membrane proteins
eng
uncontrolled
gene expression
eng
uncontrolled
bacillus subtilis
eng
uncontrolled
fluorescence microscopy
eng
uncontrolled
cell fusion
eng
uncontrolled
signal transduction
eng
uncontrolled
gene regulation
eng
uncontrolled
lipids
Medizin und Gesundheit
open_access
Institut für Molekulare Infektionsbiologie
OpenAIRE
Förderzeitraum 2015
Universität Würzburg
https://opus.bibliothek.uni-wuerzburg.de/files/12557/Lopez_journal.pgen.1005140.pdf
12965
2013
eng
6
4
article
1
2016-03-11
--
--
Overproduction of Flotillin Influences Cell Differentiation and Shape in Bacillus subtilis
ABSTRACT Bacteria organize many membrane-related signaling processes in functional microdomains that are structurally and functionally similar to the lipid rafts of eukaryotic cells. An important structural component of these microdomains is the protein flotillin, which seems to act as a chaperone in recruiting other proteins to lipid rafts to facilitate their interaction. In eukaryotic cells, the occurrence of severe diseases is often observed in combination with an overproduction of flotillin, but a functional link between these two phenomena is yet to be demonstrated. In this work, we used the bacterial model Bacillus subtilis as a tractable system to study the physiological alterations that occur in cells that overproduce flotillin. We discovered that an excess of flotillin altered specific signal transduction pathways that are associated with the membrane microdomains of bacteria. As a consequence of this, we detected significant defects in cell division and cell differentiation. These physiological alterations were in part caused by an unusual stabilization of the raft-associated protease FtsH. This report opens the possibility of using bacteria as a working model to better understand fundamental questions related to the functionality of lipid rafts.
IMPORTANCE The identification of signaling platforms in the membrane of bacteria that are functionally and structurally equivalent to eukaryotic lipid rafts reveals a level of sophistication in signal transduction and membrane organization unexpected in bacteria. It opens new and promising venues to address intricate questions related to the functionality of lipid rafts by using bacteria as a more tractable system. This is the first report that uses bacteria as a working model to investigate a fundamental question that was previously raised while studying the role of eukaryotic lipid rafts. It also provides evidence of the critical role of these signaling platforms in orchestrating diverse physiological processes in prokaryotic cells.
mBio
10.1128/mBio.00719-13
urn:nbn:de:bvb:20-opus-129653
mBio 4(6):e00719-13. doi:10.1128/ mBio.00719-13
Benjamin Mielich-Süss
Johannes Schneider
Daniel Lopez
eng
uncontrolled
bacillus subtilis
Mikroorganismen, Pilze, Algen
open_access
Institut für Molekulare Infektionsbiologie
Förderzeitraum 2014
Universität Würzburg
https://opus.bibliothek.uni-wuerzburg.de/files/12965/065_Mielich-Suess_Overproduction_of_Flotillin_Influences.pdf
11136
2013
eng
article
1
2015-03-19
--
--
Overproduction of Flotillin Influences Cell Differentiation and Shape in Bacillus subtilis
Bacteria organize many membrane-related signaling processes in functional microdomains that are structurally and functionally similar to the lipid rafts of eukaryotic cells. An important structural component of these microdomains is the protein flotillin, which seems to act as a chaperone in recruiting other proteins to lipid rafts to facilitate their interaction. In eukaryotic cells, the occurrence of severe diseases is often observed in combination with an overproduction of flotillin, but a functional link between these two phenomena is yet to be demonstrated. In this work, we used the bacterial model Bacillus subtilis as a tractable system to study the physiological alterations that occur in cells that overproduce flotillin. We discovered that an excess of flotillin altered specific signal transduction pathways that are associated with the membrane microdomains of bacteria. As a consequence of this, we detected significant defects in cell division and cell differentiation. These physiological alterations were in part caused by an unusual stabilization of the raft-associated protease FtsH. This report opens the possibility of using bacteria as a working model to better understand fundamental questions related to the functionality of lipid rafts.
IMPORTANCE The identification of signaling platforms in the membrane of bacteria that are functionally and structurally equivalent to eukaryotic lipid rafts reveals a level of sophistication in signal transduction and membrane organization unexpected in bacteria. It opens new and promising venues to address intricate questions related to the functionality of lipid rafts by using bacteria as a more tractable system. This is the first report that uses bacteria as a working model to investigate a fundamental question that was previously raised while studying the role of eukaryotic lipid rafts. It also provides evidence of the critical role of these signaling platforms in orchestrating diverse physiological processes in prokaryotic cells.
10.1128/mBio.00719-13
urn:nbn:de:bvb:20-opus-111369
mBio 4(6):e00719-13. doi:10.1128/mBio.00719-13
Zentrum für Infektionsforschung, Universität Würzburg
Daniel Lopez
Benjamin Mielich-Süss
Johannes Schneider
deu
swd
Heubacillus
deu
swd
Zelldifferenzierung
deu
swd
Faktor
Medizin und Gesundheit
open_access
Medizinische Fakultät
Universität Würzburg
https://opus.bibliothek.uni-wuerzburg.de/files/11136/036_Lopez_mBio.pdf