Raman optical activity of flagellar filaments of Salmonella: Unusually intense ROA from L-type self-assembled protein filaments and their possible higher level chiral organization

The flagellar filament of Salmonella is an assembly of a single protein, flagellin. There are different helical and straight shape filaments from wild type and mutants. Raman and Raman optical activity (ROA) spectroscopies were employed to characterize the structure of flagellar filaments. The Raman spectra of normal and two straight filaments were almost same, but in the ROA spectra, intensive ROA peaks at amide I, amide III and skeletal vibrational regions were observed from only one of two straight filaments, L-type straight filaments. When the filaments were depolymerized or fragmented, the ROA bands disappeared on the scale of the large ROA intensities. It is thought that the ROA bands of L-type flagellar filaments are related to their shape, length and possible higher level chiral organization.