Assembly and function of complex flagellar structures illustrated by the paraflagellar rod of trypanosomes.
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Animals↗
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Formation of temporary flagellar structures during insect organogenesis.
Cilia and flagella are rare in nongerminal tissues of anthropods, and are generally thought to be restricted to sperm and sensory cells in insects (2). Whitten (5) has reported the presence of kinetosomes at the base of mitotrichia in the dipteran fly Sarcophaga bullata, but reports no evidence of the organization of fibrous elements characteristic of cilia and or flagella. During an ultrastructural analysis of morphogenesis of the colleterial gland of the silk moth Hyalophora cecropia, we found the first example of paired flagella associated with an insect secretory cell. These structures are also unusual in that they serve a temporary role in morphogenesis and subsequently disappear at the terminal stages of differentiation.
Animals↗
Electron microscopic studies on the intra-flagellar structures of trypanosomes.
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Animals↗
Induction of flagellation and a novel agar-penetrating flagellar structure in Salmonella enterica grown on solid media: possible consequences for serological identification.
Salmonella enterica grown on solid medium containing iron, thiosulfate and 100 mM hexoses and amino acids underwent cell surface differentiation involving increased flagellation (electrophoretic isotypes 60, 54 and 50 kDa), conversion from rough to smooth lipopolysaccharide, and assembly of a matrix that penetrated 1.4% agar. Flagellation was also induced in the avian pathogen S. enterica var Pullorum, which is diagnostically defined as aflagellate. Induction correlated closely with a simple colonial color change when Hektoen Enteric agar was used as the basal growth medium. Group D1 egg-contaminating Salmonella grown under inducing conditions deviated from their expected H-antigen immunoreactivity, suggesting possible consequences for the interpretation of the Kauffman-White identification scheme.
Agar↗
Locations of hook-associated proteins in flagellar structures of Salmonella typhimurium.
Hooks of the flagella of Salmonella typhimurium were purified from an flaL mutant. Hook-associated proteins, namely HAP1, HAP2, and HAP3, were separated from them, and the antibody against each HAP was prepared. By immunoelectron microscopic observation, these three kinds of antiHAP antibodies were found to bind on the distal ends of hooks of filamentless mutants consistently with their composition of HAPs. The antiHAP2 antibody bound to the very tops of the claw-shaped ends of the hooks which contain all three HAPS. The antibodies against HAP1 and HAP3 bound to the basal areas and the middle areas, respectively, of the claw-shaped ends. The order of disassembly of the component proteins by heat treatment of the hook structure from the filamentless mutants was (HAP2, HAP3) greater than HAP1 greater than hook protein. These observations were consistent with our layered structure model: HAP1, HAP3, and HAP2 are assembled at the distal end of the hook in this sequence. All three HAPs were detected in the hook-filament complexes prepared from a flagellate strain. When the hook-filament structure was treated with antibody against HAP1 and with the anti-rabbit immunoglobulin G antibody, the antibody aggregate was observed in the region corresponding to the boundary between filament and hook. This observation strongly suggests that HAP1 is the protein connecting filament with hook. The locations of HAP2 and HAP3 in the hook-filament structure were not clarified with the same procedure.
Antibodies, Bacterial↗
Transformations in flagellar structure of Rhodobacter sphaeroides and possible relationship to changes in swimming speed.
Rhodobacter sphaeroides is a photosynthetic bacterium which swims by rotating a single flagellum in one direction, periodically stopping, and reorienting during these stops. Free-swimming R. sphaeroides was examined by both differential interference contrast (DIC) microscopy, which allows the flagella of swimming cells to be seen in vivo, and tracking microscopy, which tracks swimming patterns in three dimensions. DIC microscopy showed that when rotation stopped, the helical flagellum relaxed into a high-amplitude, short-wavelength coiled form, confirming previous observations. However, DIC microscopy also revealed that the coiled filament could rotate slowly, reorienting the cell before a transition back to the functional helix. The time taken to reform a functional helix depended on the rate of rotation of the helix and the length of the filament. In addition to these coiled and helical forms, a third conformation was observed: a rapidly rotating, apparently straight form. This form took shape from the cell body out and was seen to form directly from flagella that were initially in either the coiled or the helical conformation. This form was always significantly longer than the coiled or helical form from which it was derived. The resolution of DIC microscopy made it impossible to identify whether this form was genuinely in a straight conformation or was a low-amplitude, long-wavelength helix. Examination of the three-dimensional swimming pattern showed that R. sphaeroides changed speed while swimming, sometimes doubling the swimming speed between stops. The rate of acceleration out of stops was also variable. The transformations in waveform are assumed to be torsionally driven and may be related to the changes in speed measured in free-swimming cells. The roles of and mechanisms that may be involved in the transformations of filament conformations and changes in swimming speed are discussed.
Acceleration↗
Bacterial flagellar structure and function.
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Bacteria↗
Flagellar structure and function in eubacteria.
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Bacteria↗
Antigens of the subcellular fractions of Trypanosoma cruzi. II. Flagellar and membrane fraction.
A method for isolation of membrane and flagellar fractions from Trypanosoma cruzi epimastigotes, and descriptions of their ultrastructural characteristics and antigenic activity are presented. Electron-microscopic observation revealed that the membrane fraction resembled vesicles, as occurs frequently when the pressure-depressure method is used for cell disruption. The flagellar fraction revealed flagella and some membranes, both related and unrelated to the flagellar structure. Flagellar and membrane fractions had 5 and 3 precipitin lines respectively against anti-whole homogenate of T. cruzi, in double diffusion tests. One of the precipitin bands common to both fractions gave a reaction of identiy with one precipitin line of the microsomal fractions, that was not present in the mitochondrial, nuclear and cell sap fractions. Data from tests of protective activity activity obtained during a period of 3 years with whole homogenate and F and M fraction are also presented Protective activity against lethal challenge doses of trypomastigotes is strongly associated with the flagellar fraction.
Animals↗
Switch interactions control energy frustration and multiple flagellar filament structures.
Bacterial flagellar filament is a macromolecular assembly consisting of a single protein, flagellin. Bacterial swimming is controlled by the conformational transitions of this filament between left- and right-handed supercoils induced by the flagellar motor torque. We present a massive molecular dynamics simulation that was successful in constructing the atomic-level supercoil structures consistent with various experimental data and further in elucidating the detailed underlying molecular mechanisms of the polymorphic supercoiling. We have found that the following three types of interactions are keys to understanding the supercoiling mechanism. "Permanent" interactions are always maintained between subunits in the various supercoil structures. "Sliding" interactions are formed between variable hydrophilic or hydrophobic residue pairs, allowing intersubunit shear without large change in energy. The formation and breakage of "switch" interactions stabilize inter- and intrasubunit interactions, respectively. We conclude that polymorphic supercoiling is due to the energy frustration between them. The transition between supercoils is achieved by a "transform and relax" mechanism: the filament structure is geometrically transformed rapidly and then slowly relaxes to energetically metastable states by rearranging interactions.
Computer Simulation↗
Abnormal structures in the flagellar apparatus of the spermatozoa of two ferns.
The flagellar structure of spermatozoa is generally of the 9 + 2 pattern. However, in various animal species abnormalities have been found which some authors have recently suggested as being of value in systematics. Little information has, as yet, been published in this field on plants. In studying spermatogenesis, we found some abnormalities in connection with central and peripheral tubules. These abnormal structures were uncommon and affected only a few of the numerous flagella borne by a single spermatozoid. Such abnormalities do not seem to affect radically the motility of the spermatozoa, but they may have lost part of their fertilizing ability.
Male↗
Antigenic nature of bacterial flagellar hook structures.
The bacterial flagellar hook is antigenically distinct from the remainder of the flagellum. This conclusion is based on electron microscopic observation of intact flagella coated with antisera prepared with flagellar filaments and purified flagellar hooks.
Journal Article↗
Sensing structural intermediates in bacterial flagellar assembly by export of a negative regulator.
The ability of a regulatory protein to sense the integrity of the bacterial flagellar structure was investigated. In response to a defective hook-basal body complex, the anti-sigma 28 FlgM protein inhibits flagellin transcription. In cells with a functional hook-basal body complex, the flagellin genes are transcribed normally and the FlgM protein is expelled into the growth medium. In strains with a defective hook-basal body structure, FlgM is absent from the media. The presence of flagellin protein in the media is substantially reduced in strains carrying a FlgM-LacZ protein fusion, suggesting that the fusion is blocking the flagellar export apparatus. These results suggest that the FlgM protein assesses the integrity of the flagellar hook-basal body complex by itself being a substrate for export by the flagellar-specific export apparatus.
Bacterial Proteins↗
Mutational analysis of the Rhizobium lupini H13-3 and Sinorhizobium meliloti flagellin genes: importance of flagellin A for flagellar filament structure and transcriptional regulation.
Complex flagellar filaments are unusual in their fine structure composed of flagellin dimers, in their right-handed helicity, and in their rigidity, which prevents a switch of handedness. The complex filaments of Rhizobium lupini H13-3 and those of Sinorhizobium meliloti are composed of three and four flagellin (Fla) subunits, respectively. The Fla-encoding genes, named flaA through flaD, are separately transcribed from sigma(28)-specific promoters. Mutational analysis of the fla genes revealed that, in both species, FlaA is the principal flagellin and that FlaB, FlaC, and FlaD are secondary. FlaA and at least one secondary Fla protein are required for assembling a functional flagellar filament. Western analysis revealed a ratio close to 1 of FlaA to the secondary Fla proteins (= FlaX) present in wild-type extracts, suggesting that the complex filament is assembled from FlaA-FlaX heterodimers. Whenever a given mutant combination of Fla prevented the assemblage of an intact filament, the biosynthesis of flagellin decreased dramatically. As shown in S. meliloti by reporter gene analysis, it is the transcription of flaA, but not of flaB, flaC, or flaD, that was down-regulated by such abortive combinations of Fla proteins. This autoregulation of flaA is unusual. We propose that any combination of Fla subunits incapable of assembling an intact filament jams the flagellar export channel and thus prevents the escape of an (as yet unidentified) anti-sigma(28) factor that antagonizes the sigma(28)-dependent transcription of flaA.
Amino Acid Sequence↗
FliG and FliM distribution in the Salmonella typhimurium cell and flagellar basal bodies.
Salmonella typhimurium FliG and FliM are two of three proteins known to be necessary for flagellar morphogenesis as well as energization and switching of flagellar rotation. We have determined FliG and FliM levels in cellular fractions and in extended flagellar basal bodies, using antibodies raised against the purified proteins. Both proteins were found predominantly in the detergent-solubilized particulate fraction containing flagellar structures. Basal flagellar fragments could be separated from partially constructed basal bodies by gel filtration chromatography. FliG and FliM were present in an approximately equimolar ration in all gel-filtered fractions. FliG and FliM copy numbers, estimated relative to that of the hook protein from the early fractions containing long, basal, flagellar fragments, were (means +/- standard errors) 41 +/- 10 and 37 +/- 13 per flagellum, respectively. Extended structures were present in the earliest identifiable basal bodies. Immunoelectron microscopy and immunoblot gel analysis suggested that the FliG and, to a less certain degree, the FliM contents of these structures were the same as those for the complete basal bodies. These facts are consistent with the postulate that FliG and FliM affect flagellar morphogenesis as part of the extended basal structure, formation of which is necessary for assembly of more-distal components of the flagellum. The determined stoichiometries will provide important constraints to modelling energization and switching of flagellar rotation.
Bacterial Proteins↗
Structure of flagellar microtubules.
There is a widely perceived and growing need for a reliable high-resolution three-dimensional structural model of MT. One contributor to this need has been the enormous burst of new information from molecular biological manipulations of tubulin primary sequence and pattern of expression in cells. A second contributor has been the astounding progress in defining the MT-dynein motors of cytoplasmic motility. To interpret this new information in terms of MT assembly and function, we simply must have the structure of tubulin to atomic resolution and know the arrangement of tubulin in MT to an accuracy of better than 1 nm. The best experimental system for understanding the structural basis of MT-dependent motility is the eukaryotic flagellum. Therefore, the MT whose structure we need to know first is the flagellar doublet MT. The most generally accepted specific model for flagellar MT structure was proposed by Amos and Klug in 1974. The impact of their model has been enormous. It has provided the structural framework for thinking about MT function and has influenced the interpretation of a vast body of experimental observation over the intervening 15 years. As a first approximation to the structure of the native MT, in flagellar doublets and cytoplasmic singlets, it has served superbly. Now, we face an accumulation of new information on the nature of the intersubunit bond gleaned from assembly reactions of tubulin, on the nature and probable structure of nontubulin components of flagellar MT, and on the appearance of MT in their native hydrated state. We are compelled by this new evidence to look for the next approximation to the three-dimensional structure of the flagellar doublet MT. This second generation model is not yet formulated in sufficient detail to serve as a replacement for the Amos and Klug model. What we can say at this point is that the new model will be much more complex than the old one, having only axial periodicity in both A and B subfibers rather than full helical symmetry. The model must include at least one tektin filament at the medial (in the flagellum) A-B junction, and perhaps another in a location yet to be determined. It may also include other nontubulin components. The axial period of the MT itself, free of attached cross-bridging structure from the flagellum, must be at least 32.8 nm.(ABSTRACT TRUNCATED AT 400 WORDS)
Flagella↗
Flagellar motion and fine structure of the flagellar apparatus in Chlamydomonas.
The biflagellate alga Chlamydomonas reinhardi was studied with the light and electron microscopes to determine the behavior of flagella in the living cell and the structure of the basal apparatus of the flagella. During normal forward swimming the flagella beat synchronously in the same plane, as in the human swimmer's breast stroke. The form of beat is like that of cilia. Occasionally cells swim backward with the flagella undulating and trailing the cell. Thus the same flagellar apparatus produces two types of motion. The central pair of fibers of both flagella appear to lie in the same plane, which coincides with the plane of beat. The two basal bodies lie in a V configuration and are joined at the top by a striated fiber and at the bottom by two smaller fibers. From the area between the basal bodies four bands of microtubules, each containing four tubules, radiate in an X-shaped pattern, diverge, and pass under the cell membrane. Details of the complex arrangement of tubules near the basal bodies are described. It seems probable that the connecting fibers and the microtubules play structural roles and thereby maintain the alignment of the flagellar apparatus. The relation of striated fibers and microtubules to cilia and flagella is reviewed, particularly in phytoflagellates and protozoa. Structures observed in the transitional region between the basal body and flagellar shaft are described and their occurrence is reviewed. Details of structure of the flagellar shaft and flagellar tip are described, and the latter is reviewed in detail.
Eukaryota↗
Invited review: bacterial flagellar sheaths: structures in search of a function.
Although bacterial flagellar sheaths were observed over 30 years ago, they may still be characterized as structures in search of a function. In addition to true sheaths, bacterial flagella may possess other adornments that cause an increase in the organelle's cross-sectional diameter. These "complex flagella" are sharply differentiated from sheathed flagella. Immunological and chemical distinctions have been found between flagellar sheaths, flagellar cores, and LPS layers inferred to be the sheath sensu stricto. Although complex flagella may serve as specific receptors for flagellotropic phages or in allowing for more efficient swimming in viscous environments, similar functions have not yet been attributed to true sheaths. It is postulated that flagellar sheaths may allow for specific interaction between a bacterium and a surface. In addition, there is a problem as to the relationship between a rapidly rotating flagellum and the sheath.
Antigens, Bacterial↗