The fine structure of the flagellar apparatus of Chlamydomonas moewusii.
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Chlamydomonas↗
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Results for “flagellar structure”
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On the structural protein of flagellar outer fibers.
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Acrylic Resins↗
Structure of straight flagellar filaments from a mutant of Escherichia coli.
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Escherichia coli↗
Unusual structures in the flagellar apparatus of a strain of Trypanosoma cruzi.
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Animals↗
The three-dimensional structure of the flagellar rotor from a clockwise-locked mutant of Salmonella enterica serovar Typhimurium.
Three-dimensional reconstructions from electron cryomicrographs of the rotor of the flagellar motor reveal that the symmetry of individual M rings varies from 24-fold to 26-fold while that of the C rings, containing the two motor/switch proteins FliM and FliN, varies from 32-fold to 36-fold, with no apparent correlation between the symmetries of the two rings. Results from other studies provided evidence that, in addition to the transmembrane protein FliF, at least some part of the third motor/switch protein, FliG, contributes to a thickening on the face of the M ring, but there was no evidence as to whether or not any portion of FliG also contributes to the C ring. Of the four morphological features in the cross section of the C ring, the feature closest to the M ring is not present with the rotational symmetry of the rest of the C ring, but instead it has the symmetry of the M ring. We suggest that this inner feature arises from a domain of FliG. We present a hypothetical docking in which the C-terminal motor domain of FliG lies in the C ring, where it can interact intimately with FliM.
Bacterial Proteins↗
Extracellular microtubules. The origin, structure, and attachment of flagellar hairs in Fucus and Ascophyllum antherozoids.
Mastigonemes (Flimmer) from the sperm of Ascophyllum and Fucus were found to consist of a tripartite structure-a ca. 2000-A tapered basal region, a closed microtubular shaft, and a group of terminal filaments. Each of these regions appears to be constructed of globular subunits with a center-to-center distance of about 45 A. The mastigoneme microtubule is of smaller diameter (170-190 A) than cytoplasmic microtubules in these or other plant cells. During the initial stages of flagellar ontogeny, structures similar to mastigonemes (presumptive mastigonemes) are found within membrane-limited sacs in the cytoplasm or within the perinuclear space. Mastigonemes at this time are generally not found on the flagellar surface. Later, when the anterior flagellum acquires mastigonemes, the presumptive mastigonemes are absent from the cytoplasm. The regularity of attachment of mastigonemes to the flagellar surface suggests that specific attachment sites are constructed on the plasma membrane during flagellar ontogeny. No evidence for penetration of the mastigoneme through the plasma membrane was obtained. The origin and structure of mastigonemes are discussed in relation to reports of the origin and structure of other microtubular systems.
Eukaryota↗
Direct interaction of flagellin termini essential for polymorphic ability of flagellar filament.
We report the structures of flagellar filaments reconstituted from various flagellins with small terminal truncations. Flagellins from Salmonella typhimurium strains SJW1103 (wild type), SJW1660, and SJW1655 were used, which form a left-handed supercoil, the L- and R-type straight forms, respectively. Structure analyses were done by electron cryomicroscopy and helical image reconstruction with a help of x-ray fiber diffraction for determining precise helical symmetries. Truncation of either terminal region, irrespective of the original flagellin species, results in a straight filament having a helical symmetry distinct either from the L- or R-type. This filament structure is named Lt-type. Although the local subunit packing is similar in all three types, a close comparison shows that the Lt-type packing is almost identical to the R-type but distinct from the L-type, which demonstrates the strong two-state preference of the subunit interactions. The structure clearly suggests that both termini are located in the inner tube of the concentric double-tubular structure of the filament core, and their proper interaction is responsible for the correct folding of fairly large terminal regions that form the inner tube. The double tubular structure appears to be essential for the polymorphic ability of flagellar filaments, which is required for the swimming-tumbling of bacterial taxis.
Flagella↗
Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism.
The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, and its function as a nano-sized universal joint is essential for dynamic and efficient bacterial motility and taxis. It transmits the motor torque to the helical propeller over a wide range of its orientation for swimming and tumbling. Here we report a partial atomic model of the hook obtained by X-ray crystallography of FlgE31, a major proteolytic fragment of FlgE lacking unfolded terminal regions, and by electron cryomicroscopy and three-dimensional helical image reconstruction of the hook. The model reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.
Bacterial Proteins↗
The structure of the archeabacterial flagellar filament of the extreme halophile Halobacterium salinarum R1M1 and its relation to eubacterial flagellar filaments and type IV pili.
Although the phenomenology and mechanics of swimming are very similar in eubacteria and archaeabacteria (e.g. reversible rotation, helical polymorphism of the filament and formation of bundles), the dynamic flagellar filaments seem completely unrelated in terms of morphogenesis, structure and amino acid composition. Archeabacterial flagellar filaments share important features with type IV pili, which are components of retractable linear motors involved in twitching motility and cell adhesion. The archeabacterial filament is unique in: (1) having a relatively smooth surface and a small diameter of approximately 100A as compared to approximately 240A of eubacterial filaments and approximately 50A of type IV pili; (2) being glycosylated and sulfated in a pattern similar to the S-layer; (3) being synthesized as pre-flagellin with a signal-peptide cleavable by membrane peptidases upon transport; and (4) having an N terminus highly hydrophobic and homologous with that of the olygomerization domain of pilin. The synthesis of archeabacterial flagellin monomers as pre-flagellin and their post-translational, extracellular glycosylation suggest a different mode of monomer transport and polymerization at the cell-proximal end of the filament, similar to pili rather than to eubacterial flagellar filaments. The polymerization mode and small diameter may indicate the absence of a central channel in the filament. Using low-electron-dose images of cryo-negative-stained filaments, we determined the unique symmetry of the flagellar filament of the extreme halophile Halobacterium salinarum strain R1M1 and calculated a three-dimensional density map to a resolution of 19A. The map is based on layer-lines of order n=0, +10, -7, +3, -4, +6, and -1. The cross-section of the density map has a triskelion shape and is dominated by seven outer densities clustered into three groups, which are connected by lower-density arms to a dense central core surrounded by a lower-density shell. There is no evidence for a central channel. On the basis of the homology with the oligomerization domain of type IV pilin and the density distribution of the filament map, we propose a structure for the central core.
Bacterial Proteins↗
Expression of two Rhizobium meliloti flagellin genes and their contribution to the complex filament structure.
The complex flagellar filaments of Rhizobium meliloti are composed of two related (87% identical) flagellins that are encoded by closely linked, separately transcribed genes, flaA and flaB (E. Pleier and R. Schmitt, J. Bacteriol. 171:1467-1475, 1989). To elucidate the role of the subunits, A and B, in assembling the complex filament, the wild-type alleles were replaced with defective ones containing a 2,249-bp deletion (accompanied by substitution of a kanamycin resistance cartridge), which eliminates 74% of flaA (3' end) and 85% of flaB (5' end). The resulting nonmotile, filamentless mutant, RU11011, was tested for complementation with wild-type flaA, flaB, and flaA flaB genes provided on the multiple-copy vector pRK290. Whereas flaA alone did not restore motility and filament production, both flaB and flaA flaB restored 20 to 30% of wild-type motility. Apparent causes of this reduced motility were fewer flagella per cell and/or shortened filaments sometimes ending in unusually thin, fragile structures. Tests with enzyme-linked antiflagellin antibodies indicated that flaA is expressed at higher levels than flaB and that multiple copies of flaA lead to reduced flagellin export. We conclude that the proximal portion of the complex filament is assembled from B subunits (not produced sufficiently to form full-length flagella) and that the distal portion is made from A subunits. Multiple copies of the strong flaA promoter may offset transcriptional controls that regulate the synthesis of flagellar structures required for flagellin export.
Chemotaxis↗
The organization of the Caulobacter crescentus flagellar filament.
The structural organization of the flagellar filament of Caulobacter crescentus, as revealed by immunoelectron microscopy, shows five antigenically distinct regions within the hook-filament complex. The first region is the hook. The second region is adjacent to the hook and is approximately 10 nm in length. On the basis of its location in the hook-filament complex, this region may contain hook-associated proteins. Next to this is the third region, which is approximately 60 nm in length. Antibody decoration experiments using mutant strains with deletions of the structural gene for the 29 x 10(3) Mr flagellin (flgJ) showed that the presence of this region is correlated with the expression of the 29 x 10(3) Mr flagellin gene. The next region (region IV), of length approximately 1 to 2 microns, appears to contain the 27.5 x 10(3) Mr flagellin, but at its distal end includes, in gradually increasing amounts, the 25 x 10(3) Mr flagellin. The rest of the filament (region V) is made up predominantly, if not completely, of the 25 x 10(3) Mr flagellin. Except for the hook, there are no morphological features that would otherwise distinguish these regions. A functional flagellum, having the wild-type length and morphology, is assembled by mutant strains deficient in the 29 x 10(3) Mr flagellin and 27.5 x 10(3) Mr flagellin.
Antibodies, Bacterial↗
Heterogeneity and a coiled coil prediction of trypanosomatid-like flagellar rod proteins in Euglena.
The emergent flagellum of euglenoids and trypanosomatids contained in addition to microtubules a prominent filamentous structure--the flagellar rod (paraflagellar/paraxonemal rod). Immunoblots and immunofluorescence localization using three antibodies generated against gel-isolated proteins confirmed previous studies that the Euglena flagellar rod consisted of polypeptides migrating at 66-, 69-, and 75-kD. Immunoblotting after two dimensional gel electrophoresis identified ten or more isoforms of these polypeptides. Differences in migration in acrylamide gels under nonreducing and reducing conditions suggested that the rod proteins contain intramolecular disulfide linkages. Comparative peptide mapping showed that the 66-, 69-, and 75-kD polypeptides were distinct, but related proteins, and also identified a fourth related protein migrating at 64-kD. Using antibodies against rod proteins, two overlapping cDNAs were isolated and from their sequences the cDNAs were predicted to encode 334 amino acids of the 66-kD protein; the amino acid sequence had > 65% identity to the carboxyl-terminus of the trypanosomatid flagellar rod proteins. Secondary structural prediction suggested that flagellar rod proteins contain an extended segmented coiled coil stalk and two nonhelical heads. Coiled coil appeared to be an important structural motif in the construction of flagellar rod filaments.
Amino Acid Sequence↗
Basal-body-associated disks are additional structural elements of the flagellar apparatus isolated from Wolinella succinogenes.
The intact flagella of Wolinella succinogenes, a gram-negative, anaerobic bacterium with a single polar flagellum, were obtained by an improved procedure, introduced recently by Aizawa et al. (S.-J. Aizawa, G. E. Dean, C. J. Jones, R. M. Macnab, and S. Yamaguchi, J. Bacteriol. 161:836-849, 1985) for the flagellum of Salmonella typhimurium. Disks with a diameter of 130 +/- 30 nm, which were attached to the basal body of the isolated intact flagella, could be identified by electron microscopy as additional structural elements of the bacterial flagellar apparatus. In freeze-dried and metal-shadowed samples, two rings of the basal body were detected on one side and a terminal knob was located on the other side of the disks. Suspension of the flagellar apparatus in acidic solution dissociated the flagellar filaments, yielding hook-basal body complexes with and without the associated disks. If whole cells were subjected to low pH, double disks of the same diameter and with a central hole of about 13 nm could be isolated. Similar parallel disks could be seen also in negatively stained whole cells. When uranyl acetate was used for negative staining of the intact flagella, concentric rings were detected on the disks, similar to the concentric membrane rings found by Coulton and Murray (J. W. Coulton and R. G. E. Murray, J. Bacteriol. 136:1037-1049, 1978) on platelike arrays of proteins in outer membrane preparations of Aquaspirillum serpens. Because the disks of W. succinogenes can be isolated together with the flagellar hook-basal body complex, they appear to be basal-body-rather than secondary membrane-associated structures. It is possible that these disks are the bearing or stator of this rotary device.
Cell Fractionation↗
The fine structure of fertilization in the fern Marsilea vestita.
The ultrastructural details of fertilization in the fern Marsilea vestita, including gamete approach and fusion, the fate of the spermatozoid organelles and the development of a possible block to polyspermy are described. The spermatozoid approaches the egg through layers of mucilage that surround the megaspores. It moves down the neck of the archegonium into the cavity above the egg. In order to reach the egg, it must move through a small hole in the thick wall that lies across the top of the egg. The fusion of the plasma membranes of the gametes results in an outflow of egg cytoplasm into the clear space under the sperm plasma membrane, creating a fertilization cone. All the organelles of the fertilizing spermatozoid, including nucleus, mitochondrion, microtubule ribbon, multilayered structure, and flagellar band, with approximately 150 flagella, enter the egg cytoplasm. The nucleus enters as a condensed rod of chromatin with no nuclear envelope. The chromatin begins to disperse immediately and a new nuclear envelope is formed around the chromatin by egg endoplasmic reticulum. The mitochondrion and the microtubules of the ribbon and flagella are broken down, but the fates of the flagellar band and the multilayered structure have not been determined. After spermatozoid penetration, a new extracellular layer appears above the surface of the egg, beginning in the region of sperm penetration and spreading across the top of the egg. This layer may be important in preventing other spermatozoids from fusing with the egg.
Cell Fusion↗
Structural comparison of tektins and evidence for their determination of complex spacings in flagellar microtubules.
Recent structural studies indicate that a tektin heteropolymer forms a unique protofilament of flagellar microtubules. We report here the sequence of tektin C (approximately 47 kDa), predicted from its cDNA (GenBank U38523), compared to tektins A (approximately 53 kDa) and B (approximately 51 kDa) from sea urchin (Strongylocentrotus purpuratus) sperm flagellar microtubules, and compared to partial sequences reported from mouse and human. We are now able to make several observations concerning the tektin family: (1) their common structural features, (2) a comparison of their structure to intermediate filament proteins, and (3) their possible organization in the tektin filament polymer. The predicted amino acid sequence identities/similarities are: for tektins A and C, 42/54%, for tektins A and B, 34/51%; for tektins B and C, 29/42%; for tektin C and a partial cDNA clone from mouse testis, 55/65%; and for tektin B and a partial cDNA clone from the human brain, 45/47%. The three tektins (and the human clone) possess the exact sequence repeat RPNVELCRD. The structural pattern of all three tektin polypeptides is similar to intermediate filament proteins. Tektins are predicted to form extended rods composed of two alpha-helical segments (approximately 180 residues long) capable of forming coiled coils, which are interrupted by short non-helical linkers. The two segments are homologous in sequence and secondary structure, indicating a gene duplication event prior to the divergence of the three tektins. Along each tektin rod cysteine residues occur with a periodicity of approximately 8 nm, coincident with the axial repeat of tubulin dimers in microtubules. From EM data and calculations of secondary structure, the segment length of tektin AB heterodimers is likely to be 16 nm. Both segments of tektin C may be 24 nm long, but one may be 16 nm. On the basis of the available evidence, we propose that coassembly of tektin AB heterodimers with tektin C dimers produces filaments with overall repeats of 8, 16, 24, 32, 40, 48 and 96 nm, generating the basis for the complex spatial arrangements of axonemal components.
Amino Acid Sequence↗
Covalent structure of three phase-1 flagellar filament proteins of Salmonella.
Using recombinant DNA techniques, the covalent structure was determined for three flagellar filament proteins produced by Salmonella serotypes with phase-1 antigens a, c and d. Comparison of the results obtained, together with previous results for antigen i, indicated an overall structure in which conservation of amino acid sequence was absolute at both ends of the molecule and proceeded inwards with progressively greater variation. Very few differences in nucleotide sequence were detected in regions of amino acid conservation, which suggested that these areas of the gene may be involved in regulatory functions.
Amino Acid Sequence↗
Isolation and characterisation of a linked cluster of genes from Agrobacterium tumefaciens encoding proteins involved in flagellar basal-body structure.
We report the DNA sequence of 7205 bp of the Agrobacterium tumefaciens chromosome. This contains a putative operon encoding homologues of the flagellar rod and associated proteins FlgBCG and FliE, the L and P ring proteins (FlgHI) a possible flagellum-specific export protein FliP, and two proteins of unknown function, FlgA and FliL. Several of these genes have overlapping stop and start codons. Three non-flagellate Tn5-induced mutations map to this operon: fla-11 to the first gene, encoding the rod protein FlgB; fla-15 to flgA; and fla-12 to fliL. A site-specific mutation introduced into the final gene in this cluster, fliP, also resulted in a non-flagellate phenotype. This indicates that the operon is expressed, and that at least FlgB, FlgA, FliL and FliP are required for flagellar assembly in A. tumefaciens. The bulk of this operon is conserved in the same order in Rhizobium meliloti.
Agrobacterium tumefaciens↗
Additional structures associated with bacterial flagellar basal body.
By fixation of preparations prior to negative staining, we have been able to visualize additional features attached to the basal body of Salmonella typhimurium. These new features consist of arms attached to the M ring, a cap resting atop the arms, and a dome attached to the rod. These structures may be parts of the motor and/or of the putative, flagellar export apparatus. Preparations from mutant strains show that the presence of these features does not depend on the presence of the motA, motB or cheA genes.
Flagella↗