Investigation of molecular interactions in cytoskeletal systems with holographic optical tweezers [Elektronische Ressource] / vorgelegt von Kai Uhrig

Kai Uhrig

Sujets

• Biologie

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2009
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 22 Mo

Extrait

INAUGURAL - DISSERTATION
zur Erlangung der Doktorwurde der
Naturwissenschaftlich-Mathematischen Gesamtfakult at
der Ruprecht-Karls-Universit at Heidelberg
vorgelegt von
Diplom Chemiker Kai Uhrig
aus Heidelberg
Tag der mundlic hen Prufung: 6. Mai 2009Investigation of Molecular Interactions in
Cytoskeletal Systems
with
Holographic Optical Tweezers
Gutachter:
Prof. Dr. Joachim P. Spatz Priv. Doz. Dr. Dirk Herten
Physikalisch Chemisches Institut Physikalisch Chemisches Institut
Universit at Heidelberg Universit at Heidelberg
Max-Planck-Institut fur
Metallforschung, StuttgartContents
Abstract 5
I Introduction 5
1 Introduction and Outline 7
2 Theory of Optical Tweezers 11
2.1 Principle of Optical Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Geometrical Optics Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Rayleigh Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 External Factors on Particle Dynamics . . . . . . . . . . . . . . . . . . . . . 21
2.5 Calibration of Optical Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.5.1 Equipartition Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.5.2 Statistical Analysis of Position Distribution . . . . . . . . . . . . . . 24
2.5.3 Hydrodynamic Friction and Stokes Force . . . . . . . . . . . . . . . 25
2.5.4 Power Spectra Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.6 Holographic Optical Tweezers . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6.1 Multiple Trap Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6.2 Theory of Di raction and Holography . . . . . . . . . . . . . . . . . 30
2.6.3 Fourier Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.6.4 Computer Generated Holograms . . . . . . . . . . . . . . . . . . . . 32
3 Actin and the Cytoskeleton 39
3.1 Cytoskeletal Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.1 Microtubules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.2 Intermediate Filaments . . . . . . . . . . . . . . . . . . . . . . . . . 40
iiiiv Contents
3.1.3 Actin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.1.4 Biochemistry and Biology of Actin . . . . . . . . . . . . . . . . . . . 41
3.1.5 Actin Binding Proteins . . . . . . . . . . . . . . . . . . . . . . . . . 43
Myosin II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
-Actinin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.1.6 Actin Cortex and Actin Bundles . . . . . . . . . . . . . . . . . . . . 45
4 Malaria and Biophysics of the Malaria Parasite 47
4.1 History and Background of Malaria . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Biology and Life Cycle of the Malaria Parasite . . . . . . . . . . . . . . . . 49
4.3 Motility and Adhesion of Plasmodium Sporozoites . . . . . . . . . . . . . . 50
II Materials and Methods 55
5 Microscopy Setup 57
5.1 Holographic Optical Tweezers Setup . . . . . . . . . . . . . . . . . . . . . . 57
5.2 Fluorescence Microscopy Setup . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.3 Bright eld Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.1 High Magni cation Inverted Microscope Setup . . . . . . . . . . . . 61
5.3.2 Low Upright Microscope Setup . . . . . . . . . . . . . 61
5.4 Setup Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.5 Tracking Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6 Micro uidic Flow Cells 65
6.1 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.2 PDMS Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3 Assembly of Flow Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.4 Cleaning of Flow Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.5 Flow Cell Design and Scheme of Usage . . . . . . . . . . . . . . . . . . . . . 70
6.6 Surface Modi cation of Micropillars . . . . . . . . . . . . . . . . . . . . . . 71
7 Proteins and Bu er Solutions 73
7.1 Actin Isolation and Puri cation . . . . . . . . . . . . . . . . . . . . . . . . . 73
7.2 Actin Storage and Dialysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
7.3 Actin Polymerization and Staining . . . . . . . . . . . . . . . . . . . . . . . 74
7.4 -Actinin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.5 Adhesive Microparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
8 Plasmodium Sporozoite Experiments 77
8.1 Preparation of Plasmodium berghei sporozoites . . . . . . . . . . . . . . . . 77Contents v
8.2 Optical Tweezers Experiments with Sporozoites . . . . . . . . . . . . . . . . 78
III Experiments and Results 79
9 Two-Dimensional Actin Networks 81
9.1 Experimental Procedure to Create and Probe Two-Dimensional Actin Net-
works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
9.1.1 Calibration of Trap Pattern . . . . . . . . . . . . . . . . . . . . . . . 87
9.2 Contractile Forces during Cross-Linking of Actin Network . . . . . . . . . . 89
9.3 Conclusions on Two-Dimensional Actin Networks . . . . . . . . . . . . . . . 91
10 Zipping Forces Between Filaments in HOT 95
10.1 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
10.2 Data Analysis and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
10.3 Conclusions on Actin Snapping Experiments . . . . . . . . . . . . . . . . . 102
11 Unzipping Forces Between Filaments in HOT 105
11.1 Background for the Induced Unzipping of Semi exible Polymers . . . . . . 105
11.2 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
11.3 Data Analysis and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
11.4 Conclusions on Actin Unzipping Experiments using HOT . . . . . . . . . . 110
12 Unzipping Forces Between Filaments on Pillar Substrates 113
12.1 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
12.2 Data Analysis and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
12.3 Conclusions on Actin Unzipping Experiments on Pillar Substrates . . . . . 120
13 Probing Adhesion of Plasmodium Sporozoites with Optical Tweezers 123
13.1 Viability of Sporozoites in Optical Traps . . . . . . . . . . . . . . . . . . . . 124
13.2 Force Calibration for Trapped Sporozoites . . . . . . . . . . . . . . . . . . . 125
13.3 Adhesion Experiments with Plasmodium Sporozoites . . . . . . . . . . . . . 127
13.4 Results and Discussion of Sporozoite Experiments . . . . . . . . . . . . . . 128
13.5 Conclusions and Outlook for Plasmodium Experiments . . . . . . . . . . . . 131
14 Discussion and Outlook 133
List of Figures 137
Bibliography 141
A Publications 163Abstract
Optical tweezers are a versatile tool to apply and measure forces in the piconewton range on
microscopic objects that are held by optical forces in a focussed laser beam. We employed
holographic optical tweezers (HOT) to create extended force sensor arrays, consisting of
multiple trapped particles that were controlled and probed individually. The combina-
tion of high-speed video microscopy with uorescence imaging allowed the visualization
of labeled protein structures in parallel with the tracking of multiple trapped particles for
force measurements. Using this setup, we could perform quantitative force measurements
on biological samples with HOT for the rst time.
To obtain reliable force measurements, calibration methods based on power spectra analy-
sis were adapted for holographic optical tweezers. In micro uidic environments, biomimetic
structures of the cellular cytoskeleton could be reconstituted between optically trapped
microspheres. Flow cells and uidic control, developed in this work allowed the exchange
of solutions in the system and thus, the complete control of the chemical environment
without generating forces that would a ect the trapped particles.
This provided the possibility to measure dynamic processes such as the contractility of two-
dimensional cross-linked actin networks in the micro uidic ow cell. A network of actin
bers between seven trapped particles was created and the forces during cross-linking were
obtained.
To investigate bundling processes between laments, a method has been established us-
ing dynamic HOT to manipulate zipper-like structures between trapped particles actively.
Analysis of particle trajectories during zipping of laments allowed the determination of
binding energies between laments.
Unbundling forces between actin laments were measured on trapped spheres during the
active process of unzipping. Additionally, this system was transferred to actin networks
on PDMS micropillar substrates to improve feasibility. In combination with the optical
trap, this allowed for the investigation of unbundling forces for -actinin as well as for
magnesium ions as cross-linkers.
In a di erent set of experiments, the adhesion process of the Malaria causing parasite Plas-
modium was investigated. Adhesion and locomotion of the sporozoites is crucial for the
infectivity of the parasite. A methodology for laser tweeze