Browsing by Subject "Biofilm proteins"

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    ItemOpen Access
    Functional bacterial amyloid nanomaterials
    (2016-09) Önür, Tuğçe
    Mis-folded or unfolded proteins tend to aggregate and aggregated structures are called as amyloids. Amyloid formation contributes to some human diseases and resulting in death in some cases. On the other hand, functional amyloids are found in nature and they are highly ordered assembled structures and they function in cellular events. Some bacteria, fungi or yeast species synthesize these kind of functional amyloids. For example, curli proteins of Escherichia coli play a role in initial attachments for biofilm formation and contribute to stiffness of the biofilm matrix. CsgA is the major subunit while CsgB is the minor subunits which nucleates CsgA polymerization. They are capable of attachment to the abiotic or biotic surfaces. Both of them share some characteristics with non-functional amyloids. For instance, their structures are dominated by ß sheets so they have a rigid amyloid core domain that enables to resist stress factors such as proteases and detergent treatment or pH. Their stable structures and adhesive properties make them useful in materials science. Moreover, high yield could be obtained easily by using molecular biology techniques such as cloning and protein purification so they are highly cost-effective materials. In this study, CsgA and CsgB fibers were proposed as new type of functional biomaterials to do so fiber formations of CsgA and CsgB were analyzed in detail. csgA and csgB genes were cloned into expression vectors. Their ß sheet rich structures were validated with CD analysis and binding capability to Thioflavin T dye were assayed which is the general property of amyloids. Self-seeding and cross-seeding strategies were applied to analyze fiber formation and quartz crystal microbalance with dissipation (QCM-D) was used. Gold coated sensors were deposited with freshly purified proteins and polymerized. Then, sensor surfaces were monitored with SEM and AFM. With self-seeding strategies long and branched fibers were obtained from CsgA proteins while sphere like structures were formed by CsgB proteins. Also, it was concluded from the cross-seeding experiments, the order of protein addition determines the final assembled structures. Furthermore, fluorescent properties of CsgA and CsgB were analyzed in detail for the first time. Finally, binding affinity of the purified proteins to different materials (gold, silica and hydroxyapatite) were determined by using QCM-D.
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    Synthetic biogenesis of bacterial amyloid nanomaterials with tunable inorganic-organic interfaces and electrical conductivity
    (American Chemical Society, 2017) Seker U.O.S.; Chen, A. Y.; Citorik, R. J.; Lu, T. K.
    Amyloids are highly ordered, hierarchal protein nanoassemblies. Functional amyloids in bacterial biofilms, such as Escherichia coli curli fibers, are formed by the polymerization of monomeric proteins secreted into the extracellular space. Curli is synthesized by living cells, is primarily composed of the major curlin subunit CsgA, and forms biological nanofibers with high aspect ratios. Here, we explore the application of curli fibers for nanotechnology by engineering curli to mediate tunable biological interfaces with inorganic materials and to controllably form gold nanoparticles and gold nanowires. Specifically, we used cell-synthesized curli fibers as templates for nucleating and growing gold nanoparticles and showed that nanoparticle size could be modulated as a function of curli fiber gold-binding affinity. Furthermore, we demonstrated that gold nanoparticles can be preseeded onto curli fibers and followed by gold enhancement to form nanowires. Using these two approaches, we created artificial cellular systems that integrate inorganic-organic materials to achieve tunable electrical conductivity. We envision that cell-synthesized amyloid nanofibers will be useful for interfacing abiotic and biotic systems to create living functional materials.