Functional amyloid (FuBA) is produced by a large fraction of all bacterial species and represents a constructive use of the stable amyloid fold, in contrast to the pathological amyloid seen in neurodegenerative diseases. When assembled into amyloid, FuBA is unusually robust and withstands most chemicals including denaturants and SDS. Uses include strengthening of bacterial biofilms, cell-to-cell communication, cell wall construction and even bacterial warfare. Biogenesis is under tight spatio-temporal control, thanks to a simple but efficient secretion system which in E. coli, Pseudomonas and other well-studied bacteria includes a major amyloid component that is kept unfolded in the periplasm thanks to chaperones, threaded through the outer membrane via a pore protein and anchored to the cell surface through a nucleator and possibly other helper proteins. In these systems, amyloid formation is promoted through imperfect repeats, but other evolutionarily unrelated proteins either have no or only partially conserved repeats or simply consist of small peptides with multiple structural roles. This makes bioinformatics analysis challenging, though the sophisticated amyloid prediction tools developed from research in pathological amyloid together with the steady increase in identification of further examples of amyloid will strengthen genomic data mining. Functional amyloid represents an intriguing source of robust yet biodegradable materials with new properties, when combining the optimized self-assembly properties of the amyloid component with e.g. peptides with different binding properties or surface-reactive protein binders. Sophisticated patterns can also be obtained by co-incubating bacteria producing different types of amyloid, while amyloid inclusion bodies may lead to slow-release nanopills.
Keywords: Curli; Functional amyloid in Pseudomonas; Fusion proteins with binding properties; Screening systems; Sequence analysis.