Abstract
Terminal regions of flagellin, about 180 NH 2 and 100 COOH-terminal residues, are well conserved and play important roles in polymerization and polymorphism of bacterial flagellar filaments. About 65 NH 2 and 45 COOH-terminal residues are disordered in the monomeric form, but become folded upon filament formation. Taking advantage of the facts that relatively small segments can be cleaved off these disordered termini by limited proteolysis, and isolated fragments still form straight filaments, locations of those terminal segments have been mapped out in the filament structure by electron cryomicroscopy and helical image reconstruction. The fragments studied are F(1-486), F(20-494), F(1-461), F(30-461) and F(30-452). Regardless of the size and terminal side of truncation, the structures of the filaments reconstituted from the truncated fragments all have identical subunit packing arrangements of the Lt-type symmetry. Structural differences compared to the filament reconstituted from intact flagellin are found only around the filament axis, namely in the inner-tube region, and no obvious changes are observed in the outer-tube or the outer part of the filament. Truncation of only a few terminal residues results in misfolding of the inner-tube domains and their aggregation around the filament axis; further truncation reduces the densities of different parts of the aggregate. The filament reconstituted from F(30-461) fragment shows complete disappearance of the density corresponding to the inner-tube. When a further nine residues are removed, the spoke-like features left on the inner wall of the outer-tube become significantly smaller. Based on the structures and radial mass distributions of the filaments obtained, the previous amino acid sequence assignment to the morphological domains has been confirmed and further refined. The roles of terminal segments in the assembly regulation, and those of the double-tubular structure in the polymorphic mechanism are discussed.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.