Browsing by Subject "Curli"
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Item Open Access Interaction of microbial functional amyloids with solid surfaces(Elsevier BV, 2021-03) Yuca, E.; Kehribar, Ebru Şahin; Şeker, Urartu Özgür ŞafakHypothesis Self-assembling protein subunits hold great potential as biomaterials with improved functions. Among the self-assembled protein structures functional amyloids are promising unique properties such as resistance to harsh physical and chemical conditions their mechanical strength, and ease of functionalization. Curli proteins, which are functional amyloids of bacterial biofilms can be programmed as intelligent biomaterials. Experiments In order to obtain controllable curli based biomaterials for biomedical applications, and to understand role of each of the curli forming monomeric proteins (namely CsgA and CsgB from Escherichia coli) we characterized their binding kinetics to gold, hydroxyapatite, and silica surfaces. Findings We demonstrated that CsgA, CsgB, and their equimolar mixture have different binding strengths for different surfaces. On hydroxyapatite and silica surfaces, CsgB is the crucial element that determines the final adhesiveness of the CsgA-CsgB mixture. On the gold surface, on the other hand, CsgA controls the behavior of the mixture. Those findings uncover the binding behavior of curli proteins CsgA and CsgB on different biomedically valuable surfaces to obtain a more precise control on their adhesion to a targeted surface.Item Open Access Self-assembly of bacterial amyloid protein nanomaterials on solid surfaces(Academic Press, 2018) Onur, Tuğçe; Yuca, Esra; Ölmez, Tolga Tarkan; Şeker, Urartu Özgür ŞafakHypothesis: Amyloid-forming biofilm proteins of Escherichia coli, namely CsgA and CsgB, can form self-assembled nanofibers on solid surfaces. These proteins can be programmed to form bio-nanomaterials for functional applications. Experiments: In this study, the assembly of the CsgA and CsgB protein on solid surfaces was investigated in real time using a quartz crystal microbalance instrument with dissipation monitoring. The assembly kinetics of the CsgA and CsgB proteins in various settings on solid surfaces were investigated. Protein nanowires were investigated using electron microscopy. Findings: CsgA protein polymers and CsgB-added CsgA polymers form densely packed biofilm on gold surfaces, whereas CsgB polymers and CsgA-added CsgB polymers form biofilms with high water-holding capacity according to the dissipation data. Electron microscopy images of nanofibers grown on gold surfaces showed that CsgA and CsgB polymers include thicker nanofibers compared to the nanofibers formed by CsgA-CsgB protein combinations. The resulting nano/microstructures were found to have strong fluorescence signals in aqueous environments and in chloroform while conserving the protein nanowire network.Item Open Access A synthetic biology approach for engineered functional biofilm(2017-12) Kalyoncu, EbuzerExtracellular polymeric substances consist of molecules, DNAs, carbohydrates, and proteins that are secreted by microbial biofilms. These molecules assist in the synthesis of bacterial biofilms as highly ordered, complex and dynamic material systems, contribute to the adaptation of cells to their environment, and increase their flexibility and functionality under a broad range of conditions. Bacterial biofilms are promising tools for functional applications as bionanomaterials. They are synthesized by well-defined machinery, readily form fiber networks covering large areas, and can be engineered for different functionalities. One aspect of the present thesis focuses on controlling the expression of the curli proteins of Escherichia coli and functionalize the curli fibers by genetically fusing various peptide molecules. Biofilm proteins were functionalized with designed conductive aromatic aminoacids by using programmed cellular machines in order to develop electrically conductive protein nanofiber networks. It has been shown how biological conductivity can be used to control and direct metabolic activities of bacterial populations. Understanding and building conductive biological interfaces to merge living systems with electronic gadgets is a demanding subject. First time in the literature we succeeded to demonstrate living cells enabled bio-conductivity via a conductive nanofiber network formation. In E. coli, there are two proteins as backbones of the nano-fibers (CsgA and CsgB) responsible for the formation of biofilms. In this thesis, tunability of the morphology and mechanical properties of biofilm backbones were investigated by using protein engineering. The effect of minor and major proteins and their engineered form on the final mechanical properties of the biofilm structures were probed by scanning probe microscopy. The minor protein plays a crucial role in tuning the mechanical and morphological properties of the biofilm structures. Biofilm protein engineering for material science can be used through the genetically tunable biofabrication of self-assembling functional materials. Using synthetic biological tools, externally controllable biofilm patterns can be achieved. Recombinase based genetic logic gates encoding AND, and OR to control the expression of structural protein CsgA with 6x-Histaq modification were engineered with using two independent control signals. In this thesis, the opportunity to engineer bacterial biofilms using synthetic biology approaches was demonstrated.