Spider silk is a biomaterial of extraordinary toughness paired with elasticity. The assembly of silk proteins, so-called spidroins (from “spider” and “fibroin”), generates the silk threads we typically see in our garden or the corners of our houses. Although spider webs from different species vary considerably in geometry and size, many sections of spidroin sequences are conserved. Highly conserved regions, found in all spidroins, relate to the terminal domains of the protein, i.e., the N-terminal (NTD) and C-terminal domains (CTD). Both have an essential function in the silk fibre association and polymerisation. The NTD is a 14 kDa five-helix bundle, which self-associates via a pH-driven mechanism. This process is critical for starting the polymerisation of the fibre. However, detailed insights into how conserved this mechanism is in different species and the quantitative thermodynamic comparison between homologous NTDs was missing. For this reason, four homologous NTDs of the major ampullate gland (MaSp) from spider species Euprosthenops australis, Nephila clavipes, Latrodectus hesperus, and Latrodectus geometricus were investigated. I analysed and quantified equilibrium thermodynamics, kinetics of folding, and self-association. Methods involved dynamic light scattering (MALS), stopped-flow fluorescence and circular dichroism spectroscopy in combination with thermal and chemical denaturation experiments. The results showed conserved, cooperative two-state folding on a sub-millisecond time scale. All homologous NTDs showed a similarly fast association in the order of 10^9 M^−1 s^−1, while the resulting equilibrium dissociation constants were in the low nanomolar range. Electrostatic forces were found to be of great importance for protein association. Monomeric protein stability increased with salt concentration while enhancing its folding speed. However, due to Debye-Hückel effects, we found intermolecular electrostatics to be shielded, which reduced the NTDs association capacity significantly at high ionic strength. Altogether, the energetics and kinetics of the NTD dimerisation was conserved for all analysed homologs. Comparable to the NTD, the spider silks CTD is also a α-helix bundle, which covalently links two spidroins. The orientation of the domains predetermines the future fibre geometry. Here again, the detailed quantitative characterisation of the folding and dimerisation was missing. Therefore, the CTD from the E. australis was analysed in-depth. The protein folded via a three-state mechanism and was placed in the family of knotted proteins. By analysing the amino acid composition of the NTD of the MaSp1 of the Euprosthenops australis, we found an unusually high content of methionine residues (Met). To elucidate why this protein exhibits so many Met residues, I mutated all core Mets simultaneously to leucine (Leu). Results revealed a dramatically stabilised NTD, which now folded 50 times faster. After solving the tertiary structure of the mutant by NMR (nuclear magnetic resonance) spectroscopy, the structure of the monomeric mutant was found to be identical with the wild-type protein. However, when probing the dimerisation of the NTD, I could show that the association capacity was substantially impaired for the mutant. Our findings lead to the conclusion that Met provides the NTD with enhanced conformational dynamics and thus mobilises the protein, which results in tightly associated dimers. In additional experiments, I first re-introduced new Met residues into the Met-depleted protein at sequence positions containing native Leu. Hence, the mutated NTD protein was provided with the same number of Leu, which were previously removed by mutation. However, the protein did not regain wild-type characteristics. The functionality was not restored, but its stability was decreased as expected. To probe our hypothesis gained from the MaSp NTD, I transferred the experiment to another protein, namely the Hsp90 chaperone. Therefore, I incorporated methionine residues in the protein, which resulted in a slight improvement of its function. Finally, trial experiments were performed aiming at the synthesis of shortened spidroin constructs containing less repetitive middle-segments than the wild-type protein. The objective was to study the findings of the terminal domains in the context of an intact spidroin. The synthesis of these engineered spidroins was challenging. Nevertheless, preliminary results encourage the assumption that the characteristics observed in the isolated domains hold true in the context of a full-length spidroin. / Spinnenseide ist ein Biomaterial mit außergewöhnlicher Widerstandsfähigkeit welche gepaart ist mit Elastizität. Das Zusammenfügen von Seidenproteinen aus so ge-nannten Spidroinen (ein Kunstwort aus „Spinne“ und „Fibroin“) erzeugt die Seiden-fäden, die wir typischerweise in unseren Gärten oder in den Ecken unserer Häuser finden. Obwohl Spinnennetze von verschiedenen Spinnenarten in Geometrie und Größe stark variieren, sind große Teile der Spidroin-Sequenzen konserviert. Stark konservierte Bereiche, die in allen Spidroinen vorkommen, sind die endständigen Bereiche des Proteins, die N-terminale (NTD) und C-terminale Domäne (CTD) ge-nannt werden. Beide haben wichtige Funktionen in der Assoziation der Proteine im Spinnkanal und deren Polymerisation zur Ausbildung des Seidenfadens. Die NTD ist ein kleines 14 kDa Protein, bestehend aus einem Bündel aus fünf Helices, dessen Selbstorganisation pH-abhängig ist. Dieser Prozess leitet die Poly-merisation der Faser ein. Allerdings fehlten bis heute Informationen darüber, ob dieser Mechanismus bei homologen Domänen aus verschiedenen Spinnenarten konser¬viert ist, da kaum quantitative biophysikalische Daten vorhanden sind. Aus diesem Grund wurden vier homologe NTDs der Spinnenarten Euprosthenops australis, Nephila clavipes, Latrodectus hesperus und Latrodectus geometricus vergleichend untersucht und deren Gleichgewichts-Thermodynamik, die Kinetik der Faltung und die Selbstassoziation quantitativ analysiert. Dazu wurden Methoden wie dynamische Mehrwinkel-Lichtstreuung (MALS), Stopped-Flow Fluoreszenz-spektroskopie und Zirkulardichroismus in Kombination mit thermischen und chemischen Denaturierungs¬experimenten angewandt. Die Ergebnisse lieferten die Erkenntnis einer kooperativen Zwei-Zustands-Faltung, die auf einer Zeitskala von weniger als einer Millisekunde stattfand. Alle homologen NTDs zeigten eine schnelle Assoziationsratenkonstante in der Größenordnung von 10^9 M^-1 s^-1, während die Gleichgewichts-Dissoziationskonstante für alle Homologe im nied¬rigen nano-molaren Bereich lag. Die Proteinassoziation wurde durch elektrostatische Kräfte gesteuert, wobei hohe Salzkonzentrationen die Stabilität des monomeren Proteins und dessen Faltungsgeschwindigkeit erhöhten. Die Assoziation zweier Domänen wurde jedoch durch Abschirmung intermolekularer elektrostatischer Kräfte, dem Debye-Hückel-Gesetz zufolge, reduziert. Die Energetik und Kinetik der NTD-Dimerisierung aller untersuchten Homologen erwies sich konserviert. Ebenso wie die NTD, ist auch die CTD der Spinnenseide ein α-helikales Bündel, welche jedoch zwei Spidroine kovalent miteinander verbindet. Die Orientierung der verknüpften Domäne bestimmt bereits die zukünftige Faserstruktur. Ähnlich wie bei der NTD, waren Faltung und Dimerisierung der CTD bisher nicht im Detail be-schrieben. Durch eine detaillierte Analyse der CTD der E. australis konnte gezeigt werden, dass das Protein sich in einem dreistufigen Mechanismus faltet und außerdem der Familie der geknoteten Proteine angehört. Bei genauerer Betrachtung der Aminosäurezusammensetzung der E. australis NTD konnte ein ungewöhnlich hoher Anteil der Aminosäure Methionin (Met) festge¬stellt werden. Um diesen überraschenden Sachverhalt zu verstehen, habe ich alle im Kern liegenden Met zu Leucin (Leu) mutiert. Die Ergebnisse zeigten eine extrem stabilisierte NTD, welche sich nun 50-fach schneller faltete. Die Protein¬struktur der Mutante wurde in Lösung mittels NMR Spektroskopie ermittelt. Das Ergebnis lieferte deckungsgleiche Strukturen von Mutante und Wildtyp im monomeren Zustand. Allerdings zeigten NTD Dimerisierungs-Versuche, dass die Assoziations-fähigkeit der Mutante erheblich beeinträchtigt war. Untersuchungen der nativen Dynamik mittels NMR und Fluoreszenzkorrelationsspektroskopie zeigten, dass Met diese entscheidend verstärkt, was zu einem eng assoziierten Dimer führte. Im Versuch die Dynamik wieder künstlich herzustellen, habe ich neue Met in die Mutante eingeführt, auf Sequenzpositionen welche natürlicherweise Leu aufweisen. Somit wurde die ursprüngliche Anzahl an Met in der NTD wiederher¬gestellt, jedoch an anderen Positionen. Obwohl das Protein wie erwartet an Stabilität verlor, konnte dessen Funktionalität nicht wiederhergestellt werden. Um unsere Erkenntnisse auf andere Proteine zu übertragen, wurden Met Reste künstlich in ein Hsp90 Protein eingeführt. Es konnte eine leicht verbesserte Funktionalität des Proteins beobachtet werden. Schließlich wurde versucht, die für die CTD und NTD gewonnen Erkenntnisse auf intakte, jedoch verkürzte Spidroine zu übertragen. Dazu wurden Spidroine mit weniger repetitiven Mittelsegmenten mittels rekombinanten Methoden hergestellt. Die Synthese dieser Spidroine erwies sich als Herausforderung. Allerdings zeigten die vorläufigen Ergebnisse, dass eine Verallgemeinerung der Erkenntnisse der isolierten Domänen auf das Volllängen-Spidroin möglich ist.

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Spider silk is one of the most fascinating materials found in nature. Besides its properties like biodegradability, low immunoreactivity, and biocompatibility, especially the mechanical properties outperforming today’s artificial high-tech materials like Kevlar® are of great interest in biomedicine or material science. Spider silk comprises highly repetitive amino acid sequence motives, whose structure is accepted to be responsible for the extraordinary properties of spider silk. Typically, hydrophilic sequence motives alternate with hydrophobic ones making spider silk proteins resemble block copolymers. Additionally, the simple amino acid sequence and the possibility to form fibrillar structures are common characteristics of spider silk proteins as well as intrinsically disordered proteins (IDP) or protein regions (IDR). Both are suspected of being involved in the development of certain neurodegenerative diseases like Alzheimer´s disease. These aspects open promising possibilities of the use of spider silk proteins in nanotechnology, but also as model systems for the fibrillization processes of IDPs and IDRs, which are still unresolved today. Currently, most of the research and application is focused on 1-dimensional spider silk protein fibrils and fibers or 0-dimensional spider silk particles. However, 2-dimensional spider silk protein films or porous 3-dimensional objects are highly relevant platforms with the potential for cell-supporting scaffolds, biodegradable electrolyte materials in transistors, or e.g., planar drug-eluting implant coatings. Generally, the effects of sequence-based and external influences on the self-assembly and folding of spider silk proteins have not yet been fully elucidated in all of these various dimensional spider silk materials, even concerning IDP and IDR models. Thus, basic research regarding assembly and folding processes is still needed, especially in films. Particularly, 2-dimensional films allow a broad spectrum of (surface) analytical techniques, from whose outcome general structure-property relations of spider silk materials across all material dimensions can be obtained. In this work, engineered spider silk proteins, which are based on the consensus sequence motives in the spider silk fibroin (spidroin) 3 and 4 of the European garden spider Araneus diadematus (eADF4(Cx), eADF3(AQ)x, eADF3(QAQ)x) as well as blends of two short peptides with the respective aa sequence of the hydrophobic (pep-c) and hydrophilic (pep-a) part of eADF4(Cx) proteins were used. Spider silk-related proteins and peptides were dissolved in 1,1,1,3,3,3-hexafluoroisopropanol or formic acid, processed as thin films, and post-treated with methanol vapor to induce β-sheet formation. Dichroic FTIR-spectroscopy was used, a powerful tool for studying protein secondary structure formation and orientation. Proteins reveal characteristic amide bands, which are highly sensitive to the conformation of the protein backbone. In the course of this work, a set of components for the line shape analysis (LSA) of the Amide I band was developed. Therby, each component was assigned to a typical secondary structure allowing a quantitative determination of the respective portions and their structural orientation. Quantitative secondary structure portions and their orientation could be determined on this basis. Furthermore, a comprehensive study of folding and self-assembly-influencing parameters like hydrophobic and hydrophilic sequences, molecular weight, the repeating sequence motive order, the film thickness, surface topography, and the surface chemistry in engineered spider silk protein and spider silk protein-based films was carried out. In general, methanol vapor post-treatment induced the formation of β-sheet structures in all films, causing phase separation and the formation of spherical and filamentous structures. The phase separation upon post-treatment was influenced by the covalent connectivity between hydrophobic and hydrophilic sequence parts as well as the repeating sequence motives. In thin films, the increased flexibility of shorter peptides enabled the formation of multipack filaments instead of spherical structures, which were formed by higher molecular weight proteins with several inter-connected repeating sequence motives. Stamping wrinkled structures using poly(dimethylsiloxane) substrates was possible. Filamentous structures were successfully assigned to β-sheet rich structures using infrared nanospectroscopy for the first time. Further, enhanced surface hydrophobicity led to the clustering of β-sheet filaments. The β-sheet content could be controlled by the amount of hydrophobic sequences in thin films. With a higher amount of hydrophobic sequences in the proteins or blends, the β-sheet content increased until a maximum β-sheet content of around 60% was reached. Additionally, β-sheet formation could be suppressed by increasing substrate hydrophobicity or by decreasing the number of repeating sequence motives by going from protein-like folding to peptide-like self-assembly. The backfolding of proteins with covalently linked repeating sequence motives further promoted the formation of more antiparallel β-sheets. Antiparallel β-sheet formation was also favored when the portion of the hydrophilic, amorphous phase was increased. Micrometer thick films did not reveal any preferred alignment of β-sheets, while a general out-of-plane orientation of β-sheets could be obtained in all thin protein, peptide, and blend films. Z-axial orientation in films was increased by using short pep-c and pep-a peptides, higher molecular weight proteins or the deposition of monolayered films instead of thin multilayered films. Also, increased hydrophilicity of the substrate promoted the alignment of β-sheets perpendicular to the substrate surface. The folding kinetics and final domain size were found to be directly correlated. The amount of hydrophobic phase, backfolding, and increased flexibility due to low chain lengths increased the folding kinetics and led to smaller domain sizes. Thus, competing effects of backfolding and flexibility of the protein/peptide backbone could be rationalized. The film integrity and water contact angle were directly related to the β-sheet content and the molecular weight. Beyond the classical protein conformation and orientation analysis, the possibilities and limits of orientation analysis using dichroic attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy were elaborated on the seemingly ideal oriented polymer model system of end-grafted poly(N,N-dimethylaminoethylmethacrylate) chains. Such a system featured a polymer brush regime in the swollen state with z-axial orientation expected similarly high as thin spider silk films after ptm. Moreover, dichroic ATR-FTIR spectroscopy is a promising analytical method for closing gaps in the defined assignment of brush regimes. In summary, general models of the structure formation and self-assembly of spider silk protein in films depending on the parameters mentioned above could be developed and set in relation to IDP/IDR self-assembly by using dichroic FTIR spectroscopy as the basic analysis method. The herein postulated models on the molecular level contribute to the understanding and development of future industrial applications of spider silk protein-based materials and the clarification of unresolved questions regarding IDP and IDR systems.:Abstract V Kurzfassung IX List of Publications XIII Publications in Trade Journals XIII Presentations and Posters XIII Contribution to Joint Publications XV List of Abbrevations XVII List of Symbols XIX List of Figures XXV List of Tables XXXIII 1 Introduction and Motivation 1 2 Theory 5 2.1 Proteins and Peptides 5 2.1.1 General Definition of Proteins and Peptides 5 2.1.2 Structure of Globular Proteins 7 2.1.3 Protein Folding 10 2.1.4 Intrinsically Disordered Proteins and Protein Regions 11 2.2 Block Copolymers 14 2.3 Spiders and Spider Silks 17 2.3.1 Classification of Spiders 17 2.3.2 The Natural Spider Silk Spinning Process 18 2.3.3 Structure of Spider Silk and Spider Silk Proteins 19 2.3.4 Structure-Property Relationships of Spider Silk 21 2.4 Infrared Spectroscopy 23 2.4.1 Basic Principles of Infrared Spectroscopy 23 2.4.2 Basic Equipment and IR-Technologies 27 2.4.3 Orientation Analysis using Dichroic FTIR Spectroscopy 32 2.4.4 Infrared Spectroscopy of Proteins and Peptides 38 2.4.5 Quantitative Analysis of TRANS- and ATR-FTIR Protein Spectra 43 2.5 Electronic Circular Dichroism 46 2.5.1 Basics Principles of Circular Dichroism 46 2.5.2 Circular Dichroism of Proteins and Polypeptides 48 2.5.3 Spectra Analysis 50 2.6 Atomic Force Microscopy 51 2.6.1 Setup of Atomic Force Microscopes 51 2.6.2 Basic Principles of Atomic Force Microscopy 52 2.6.3 AFM Operation Modes 55 3 Experimental Section 57 3.1 Materials 57 3.1.1 Chemicals 57 3.1.2 Substrates 57 3.1.3 Film Preparation 58 3.2 Analytical Methods 60 3.2.1 Dichroic FTIR Spectroscopy 60 3.2.2 Atomic Force Microscopy 64 3.2.3 Electronic Circular Dichroism 64 3.2.4 Spectroscopic Ellipsometry 64 3.2.5 Infrared Nanospectroscopy 65 3.2.6 Grazing Incident Small Angle X-Ray Scattering 66 4 Results 67 4.1 Self-Assembly of eADF4(C16) Films 67 4.1.1 Motivation 67 4.1.2 Dichroic FTIR Spectroscopy Characterization of ß-sheet Orientation in Spider Silk Films on Silicon Substrates 68 4.2 Influence of the Hydrophilic and Hydrophobic Blocks on Peptide Self-Assembly 90 4.2.1 Motivation 90 4.2.2 β-Sheet Structure Formation within Binary Blends of Two Spider Silk Related Peptides 90 4.2.3 Influence of the Hydrophilic and Hydrophobic Blocks on the Inner Morphology in Spider Silk Protein Based Blend Films 122 4.3 Influence of the Sequence Motive Repeating Number on Spider Silk Protein Folding 123 4.3.1 Motivation 123 4.3.2 Influence of Sequence Motive Repeating Number on Protein Folding in Spider Silk Protein Films 124 4.4 Influence of the Module Order on Spider Silk Protein Self-Assembly 152 4.4.1 Motivation 152 4.4.2 Secondary Structure upon Post-treatment 153 4.4.3 β-Sheet Orientation after Post-treatment 157 4.4.4 Morphology and Surface Properties 158 4.4.5 Conclusion 160 4.5 Surface Induced Changes of Spider Silk Protein Self-Assembly 161 4.5.1 Motivation 161 4.5.2 Variation of the Substrate Surface Chemistry and Topography 161 4.5.3 Influence of the Surface Topography on Protein Self-Assembly 162 4.5.4 Influence of the Surface Chemistry on Protein Self-Assembly 164 4.5.5 Conclusion 169 4.6 Chances and Limits of Dichroic ATR-FTIR Spectroscopy 170 4.6.1 Motivation 170 4.6.2 Novel Insights into Swelling and Orientation of End-Grafted PDMAEMA Chains by In-Situ ATR-FTIR Complementing In-Situ Ellipsometry 171 5 Conclusion and Outlook 197 6 References 203 7 Appendix 219 8 Danksagung 227 9 Eidesstattliche Versicherung 229

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