Microbial amyloids as functional biomaterials

Abstract

Amyloids are fibrillar aggregations of proteins, dominated by β-sheets in the structure. Although amyloids are historically associated with disorders, they emerged as outstanding biomaterials due to their high mechanical strength and rigidity that provides resistance to physical and chemical stress. Also, amyloids can easily be functionalized with peptide groups using genetic engineering approaches. Ease of functionalization in addition to aforementioned properties makes amyloid fibers excellent candidates for biomaterials with desired characteristics. In this thesis, we focused on recombinant production, characterization and functionalization of several amyloid proteins from different microorganisms. Binding behavior of amyloid fibrils on medically relevant surfaces are critical for controlling the coating characteristics and desired surface properties of biomaterials. For this reason, we firstly characterized the binding kinetics of CsgA and CsgB curli proteins on silica, gold and hydroxyapatite surfaces to precisely control their surface adhesion. According to the physicochemical properties of surfaces, CsgA, CsgB and their mixture displayed different binding behavior. Furthermore, functionalization of amyloid fibers to enhance their binding kinetics to surfaces and to organisms may hold great potentials for biomaterial applications. From this perspective, we hypothesized that glycosylation could enhance surface adhesiveness of curli fibers. For this purpose, TasA protein is engineered to obtain a glycosylation site and TasA fibers depicted an increased adhesiveness to gold surfaces upon glycosylation. Finally, we functionalized CsgA curli fibers with RGD peptide to increase adhesiveness to living cells. RGD peptide addition caused a significant increase in the adhesiveness of mammalian cells onto coated surfaces. In conclusion, amyloid proteins can serve as superior biomaterials with desired functions and characteristics. Physicochemical properties of surfaces and proteins can have essential impacts on their interaction. In order to diversify those properties, amyloid fibers can be functionalized for specific purposes such as improved surface and cell adhesion. Characterization of protein/surface interactions for amyloid proteins provides important clues for optimal biomaterial surface design and functionalization with different peptide groups can extend their application capacity as superior biomaterials.