IDENTIFICATION OF A COMMON STRUCTURAL MOTIF IN THE DISORDERED N-TERMINAL REGION OF BACTERIAL FLAGELLINS - EVIDENCE FOR A NEW CLASS OF FIBRIL-FORMING PEPTIDES

Flagellin proteins lacking the N- or C-terminus form polymers of reduc ed filament stability and straight morphology, in contrast to the coil ed native flagella. Tn the present study, the N-terminal amino acid se quence of flagellins of the anaerobic beer spoilage bacteria Pectinatu s cerevisiiphilus and Pectinatus frisingiensis as well as Enterobacter aerogenes and Pseudomonas sp. were determined. Sequence similarity wa s revealed between these and the N-termini of all known eubacterial fl agellins. Synthetic peptides corresponding to the first 15 amino acid residues of the flagellins of Pectinatus, Campylobacter jejuni, E. aer ogenes or Proteus mirabilis flagellins had a spontaneous tendency unde r physiological conditions to form 4-6 nm broad, 1-2 mu m long fibrill ar structures that had a tendency to form clusters. In contrast, the P ectinatus peptide missing residues 1-3 did not form fibrils. The pepti de missing residues 13-15 formed fibrils less easily, and the peptide missing residues 11-15 formed fibrils almost without clustering. In el ectron micrographs, the fibrillisation of the bacterial flagellar pept ides resembled that of beta-amyloid and prion peptides. H-1-NMR and in frared spectroscopy studies with homology analysis indicate that altho ugh the flagellar N-terminal peptides are flexible with many conformat ional minima, they have a significant tendency to form beta-type struc tures and a loop in the middle of the peptide. The hydrophobic charact er of the N-terminus together with the property of forming a conserved beta-strand-loop-beta-strand motif may be related to a mechanism invo lved in attaining the proper morphology and stability of the flagellar filament, by providing a device for facilitating the attachment of th e flagellin monomers to each other. The flagellar peptides represent a new class of fibril-forming peptides.