Ultrastructure and biochemical studies of the flagellar sheath of Helicobacter pylori

Helicobacter pylori flagellar sheaths were isolated by sucrose density-gradient centrifugation and analysed by electronmicroscopy, SDS-PAGE and gas-liquid chromatography. Electronmicroscopy of thin sections of flagella showed an internal electron-dense filament and a surrounding flagellar sheath with the typical bilayer structure of a membrane. The flagellar filaments could be disintegrated by acid treatment and the resulting isolated flagellar sheaths formed vesicles, sometimes with characteristic structures. Centrifugation of flagellar preparations after acid treatment resulted in the enrichment of flagellar sheaths in the pellet. SDS-PAGE analysis of the pellet showed a reduction of the flagellin band and a number of protein bands of 150, 76, 67, 65, 53, 51, 49, 29.5, 18, 17 and 16 kDa. However, there were no major protein bands characteristic for the sheath. Differences between the protein profiles of Sarkosyl-insoluble membranes and flagellar sheaths appeared in the lower M(r) range of 30-14 kDa. Major fatty acids of isolated flagellar sheaths were C 14:0, C 19:0 cyc, C 18:0, and the LPS-specific fatty acids 3-OH C 16:0 and 3-OH C 18:0. The results demonstrate that the flagellar sheaths of H. pylori are membranes and contain LPS and proteins.