Raman spectroscopic study on the L-type straight flagellar filament of Salmonella

Abstract

Structural characterization of the L-type straight flagellar filament of Salmonella was attempted with the use of Raman spectroscopy as the groundwork for addressing the structural basis responsible for molecular assembly and polymorphic transformation of the flagella filament that is a supramolecular assembly of a single protein molecule, flagellin. When the filament was depolymerized to flagellin monomer by heating, the amide I band showed remarkable upshift from 1653 to 1662 cm −1 with broadening, whereas the frequency of the amide III band kept unchanged at ∼1248 cm −1. According to the experience rules on Raman frequency-structure relation, the spectral properties in the amide I and III regions are not necessarily in agreement with the structural features suggested by other analytical techniques on the structure. Further investigations on the vibrational spectra of the flagellar filament would be very helpful for re-examining the relationships between protein secondary structures and Raman frequency in the amide I and III regions.