TY - JOUR
T1 - FliN is a major structural protein of the C-ring in the Salmonella typhimurium flagellar basal body
AU - Zhao, Ronghao
AU - Pathak, Naveen
AU - Jaffe, Howard
AU - Reese, Thomas S.
AU - Khan, Shahid
N1 - Funding Information:
We thank Premraj Makkuni for participation in initial stages of this work and John Chludzinski for expert photographic assistance. Supported, in part, by grants from the National Institutes of Health (RO1-GM36936 to S.K.) and the W. M. Keck Foundation.
PY - 1996/8/16
Y1 - 1996/8/16
N2 - The Salmonella typhimurium FliN protein has been proposed to form a mutually interacting complex with FliG and FliM, the switch complex, that is required for flagellar morphogenesis and function. We have used affinity chromatography for purification of extended flagellar basal bodies sufficient for quantitative analysis of their protein composition. The belied, extended structure is predominantly comprised of the switch complex proteins; with FliN present in the most copies (111 ± 13). This explains why single, missense fliN, fliG or fliM mutations, found in many non-motile strains, can alter the belied morphology. Cell lysates from these strains contained the wild-type complement of FliG, FliM and FliN; but the basal bodies lacked the outer, cytoplasmic(C)-ring of the bell and were separated by sedimentation from FliM and FliN. The amount of FliG present in basal bodies from wild-type and one such mutant, FliN100LP, was comparable. These data show that: (1) the mutations define a FliG and FliMfliN multiple contact interface important for motility. (2) FliG is responsible for the increased size of the membrane-embedded MS-ring complex of belied relative to acid-treated basal bodies. (3) FliN, together with FliM, account for most of the C-ring. As a major component of the C-ring, FliN is distinct from the other proteins implicated in axial flagellar protein export. Inner, cytoplasmic rod basal substructure, seen by negative-stain and quick-freeze replica electron microscopy, may gate such export. Lack of connectivity between the cytoplasmic rod and ring substructures places contacts between FliG and FliMFliN at the periphery of the basal body, proximal to the flagellar intramembrane ring particles. This topology is consistent with models where torque results from interaction of circumferential arrays of the switch complex proteins with the ring particles.
AB - The Salmonella typhimurium FliN protein has been proposed to form a mutually interacting complex with FliG and FliM, the switch complex, that is required for flagellar morphogenesis and function. We have used affinity chromatography for purification of extended flagellar basal bodies sufficient for quantitative analysis of their protein composition. The belied, extended structure is predominantly comprised of the switch complex proteins; with FliN present in the most copies (111 ± 13). This explains why single, missense fliN, fliG or fliM mutations, found in many non-motile strains, can alter the belied morphology. Cell lysates from these strains contained the wild-type complement of FliG, FliM and FliN; but the basal bodies lacked the outer, cytoplasmic(C)-ring of the bell and were separated by sedimentation from FliM and FliN. The amount of FliG present in basal bodies from wild-type and one such mutant, FliN100LP, was comparable. These data show that: (1) the mutations define a FliG and FliMfliN multiple contact interface important for motility. (2) FliG is responsible for the increased size of the membrane-embedded MS-ring complex of belied relative to acid-treated basal bodies. (3) FliN, together with FliM, account for most of the C-ring. As a major component of the C-ring, FliN is distinct from the other proteins implicated in axial flagellar protein export. Inner, cytoplasmic rod basal substructure, seen by negative-stain and quick-freeze replica electron microscopy, may gate such export. Lack of connectivity between the cytoplasmic rod and ring substructures places contacts between FliG and FliMFliN at the periphery of the basal body, proximal to the flagellar intramembrane ring particles. This topology is consistent with models where torque results from interaction of circumferential arrays of the switch complex proteins with the ring particles.
KW - Chromatography
KW - Electron microscopy
KW - Macromolecular assembly
KW - Molecular motor
KW - Protein export
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U2 - 10.1006/jmbi.1996.0452
DO - 10.1006/jmbi.1996.0452
M3 - Article
C2 - 8757287
AN - SCOPUS:0030590265
SN - 0022-2836
VL - 261
SP - 195
EP - 208
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 2
ER -