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Publié par | johannes_gutenberg-universitat_mainz |
Publié le | 01 janvier 2008 |
Nombre de lectures | 27 |
Langue | English |
Poids de l'ouvrage | 5 Mo |
Extrait
Dissertation
zur Erlangung des Grades
“Doktor der Naturwissenschaften”
am Fachbereich
Chemie, Pharmazie und Geowissenschaften
der Johannes Gutenberg‐Universität Mainz
vorgelegt von
Matthias Janke
geboren in Backnang
Mainz, 2008
Dekan: Prof. Dr. W. Hofmeister
Erster Gutachter: Prof. Dr. A. Janshoff
Zweiter Gutachter: Prof. Dr. H.‐J. Butt
Tag der mündlichen Prüfung: 08.05.2008
Abstract
This thesis was driven by the ambition to create suitable model systems that mimic
complex processes in nature, like intramolecular transitions, such as unfolding and
refolding of proteins, or intermolecular interactions between different cell compo‐
nents. Novel biophysical approaches were adopted by employing atomic force mi‐
croscopy AFM; as the main measurement technique due to its bro ad diversity.
Thus, high‐resolution imaging, adhesion measurements, and single‐molecule force
distance experiments were performed on the verge of the instrumental capabilities.
As first objective, the interaction between plasma membrane and cytoskeleton, me‐
diated by the linker protein ezrin, was pursued. Therefore, the adsorption process
and the lateral organization of ezrin on PIP containing solid‐supported membranes 2
were characterized and quantified as a fundament for the establishment of a bio‐
mimetic model system. As second component of the model system, actin filaments
were coated on functionalized colloidal probes attached on cantilevers, serving as
sensor elements. The zealous endeavor of creating this complex biomimetic system
was rewarded by successful investigation of the activation process of ezrin. As a re‐
sult, it can be stated that ezrin is activated by solely binding to PIP without any fur‐2
ther stimulating agents. Additional cofactors may stabilize and prolong the active
conformation but are not essentially required for triggering ezrin’s transformation
into an active conformation.
In the second project, single‐molecule force distance experiments were performed
on bis‐loop tetra‐urea calix4ar ene‐catenanes with different loading rates increase
in force per second. These macromolecules were specifically designed to investi‐
gate the rupture and rejoining mechanism of hydrogen bonds under external load.
The entangled loops of capsule‐like molecules locked the unbound state of intramo‐
lecular hydrogen bonds mechanically, rendering a rebinding observable on the ex‐
perimental time scale. In conjunction with Molecular Dynamics simulations, a three‐
well potential of the bond rupture process was established and all kinetically rele‐
vant parameters of the experiments were determined by means of Monte Carlo si‐
mulations and stochastic modeling.
In summary, it can be stated that atomic force microscopy is an invaluable tool to
scrutinize relevant processes in nature, such as investigating activation mechanisms
in proteins, as shown by analysis of the interaction between F‐actin and ezrin, as
well as exploring fundamental properties of single hydrogen bon ds that are of
paramount interest for the compl ete understanding of complex supramolecular
structures.
TABLE OF CONTENTS
1 INTRODUCTION 1
2 ATOMIC FORCE MICROSCOPY 4
2.1 IMAGING SURFACES 5
CONTACT MODE 5
TAPPING MODE : INTERMITTENT CONTACT MODE OR AC MODE 6
2.2 FORCE DISTANCE MEASUREMENTS 8
CANTILEVER CALIBRATION 9
COLLOIDAL PROBE MICROSCOPY CPM 11
HYDRODYNAMIC IMPACT ON THE APPROACH OF A SPHERE TO A SURFACE IN FLUIDS 12
3 EXPERIMENTAL PROCEDURES 15
3.1 SUBSTRATES 15
OXIDIZED SILICON WAFERS 16
ULTRAFLAT : MICA‐STRIPPED; GOLD 17
3.2 MATERIALS AND SAMPLE PREPARATION: EZRIN‐ACTIN EXPERIMENTS 18
PROTEIN PURIFICATION 18
PREPARATION OF SOLID‐SUPPORTED MEMBRANES AND EZRIN ADSORPTION 18
ELLIPSOMETRY 19
ATOMIC FORCE MICROSCOPY – IMAGING OF THE EZRIN ADSORPTION 19
ACTIN POLYMERIZATION 19
FLUORESCENCE MICROSCOPY 20
COLLOIDAL PROBE MICROSCOPY: CANTILEVER‐BEAD PREPARATION AND FUNCTIONALIZATION 20
ATOMIC FORCE MICROSCOPY / COLLOIDAL PROBE MICROSCOPY CPM 20
3.3 MATERIALS AND SAMPLE PREPARATION: CALIXARENE EXPERIMENTS 21
SYNTHESIS OVERVIEW 21
IMAGING OF SELF‐ASSEMBLED BIS‐TETRA‐UREA CALIX4 ARENES 22
SINGLE MOLECULE FORCE DISTANCE EXPERIMENTS 23
TABLE OF CONTENTS
4 INTERACTION OF EZRIN WITH PIP CONTAINING MEMBRANES AND F‐ACTIN 24 2
4.1 FUNDAMENTALS 24
THE LIPID PHOSPHATIDYLINOSITOL 4,5‐BISPHOSPHATE PIP 24 2
EZRIN AND THE ERM‐PROTEIN FAMILY 25
ACTIN: STRUCTURE AND FUNCTION 28
4.2 EXPERIMENTAL RESULTS & DISCUSSION:
ADSORPTION OF EZRIN ON SOLID‐SUPPORTED MEMBRANES SSM 30
FORMATION OF SOLID‐SUPPORTED MEMBRANES 30
COOPERATIVE ADSORPTION OF EZRIN ON PIP CONTAINING MEMBRANES 32 2
REVERSIBILITY OF EZRIN ADSORPTION 36
DISCUSSION 38
ADSORPTION OF EZRIN ON DOGS NI‐NTA CONTAINING MEMBRANES 39
4.3 EXPERIMENTAL RESULTS & DISCUSSION:
INTERACTION BETWEEN MEMBRANE‐BOUND EZRIN AND ACTIN FILAMENTS 42
INVESTIGATION OF F‐ACTIN BINDING TO EZRIN‐MONOLAYERS
ON SSM BY EPIFLUORESCENCE MICROSCOPY 43
FUNCTIONALIZATION OF THE CANTILEVER MICROSPHERES WITH F‐ACTIN 45
ADHESION MEASUREMENTS PERFORMED BY COLLOIDAL PROBE MICROSCOPY 47
ADHESION ANALYSIS 51
DISCUSSION 53
5 UNFOLDING AND REFOLDING OF NANOCAPSULES
AS A NEW PATHWAY OF BIOMIMETIC MODELING 57
5.1 CALIXARENES: PROPERTIES & FUNCTIONS 61
5.2 EXPERIMENTAL RESULTS & DISCUSSION:
IMAGING OF SELF‐ASSEMBLED BIS‐TETRA‐UREA CALIX4 ARENES 63
5.3 SINGLE MOLECULE FORCE SPECTR