Equilibrium energy analysis of freeze-fracture planes in membranes

Kell, Michael J.; DeFelice, Louis J.; Goolsby, William N.

doi:10.1016/s0022-5193(85)80009-6

Cited by 8 publications

(2 citation statements)

References 49 publications

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“…Freeze-fracture experiments provide unique views of membrane interiors. The technique is based on the fact that lipid bilayers separate easily upon mechanical shear at low tem-2170 MINIREVIEW perature (<-100'C) and pressure (<10-4 Pa) (29). Doublereplica methods allow examination of the complementarity (i.e., the match of particles on one face to complementary pits on the other) of the two membrane halves, a feature lost in knife-fractured replicas.…”

Section: Methodsmentioning

confidence: 99%

Gene to ultrastructure: the case of the flagellar basal body

Khan

1993

J Bacteriol

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Section: Methodsmentioning

confidence: 99%

Gene to ultrastructure: the case of the flagellar basal body

Khan

1993

J Bacteriol

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“…In our freeze-fracture preparations, the flagellar intramembrane ring particles are found on the P-fracture face. This suggests that the rings form associations with the cytoplasmic components of the flagellar base (36), even though the nature of the contacts is presently unclear. The ring particles could contact the periphery of the M/S ring (27.5-nm diameter [1Sa]), which may lie within or against the cytoplasmic membrane.…”

Section: Methodsmentioning

confidence: 99%

New structural features of the flagellar base in Salmonella typhimurium revealed by rapid-freeze electron microscopy

Khan

Reese

1991

J Bacteriol

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The structure of the flagellar base in SalmoneUla typhimurium has been studied by rapid-freeze techniques.Freeze-substituted thin sections and freeze-etched replicas of cell envelope preparations have provided complementary information about the flagellar base. The flagellar base has a bell-shaped extension reaching as far as 50 nm into the bacterial cytoplasm. This structure can be recognized in intact bacteria but was studied in detail in cell envelopes, where some flagella lacking parts of the bell were helpful in understanding its substructure. Structural relationships may be inferred between this cytoplasmic component of the flagellum and the recently described flagellar intramembrane particle rings as well as the structures associated with the basal body in isolated, chemically fixed flagella.The bacterial flagellum is a remarkable locomotory organelle whose assembly and function have been extensively studied (37,46). The flagellum is composed of an external, helical filament connected by what may be a flexible coupling, the hook, to basal structures within and beneath the plasma membrane. The flagellar base harbors the machinery for filament rotation, chemotactic signal reception, and flagellar protein export. Flagellar rotation is energized by transmembrane proton (49) or cation (28, 45) gradients. The structural modules coupling the energy derived from downhill ion transport to force generation must form part of the membrane-associated base.Bacteria migrate by modulation of the directional bias of individual flagellar motors (47). A molecular switch appears to change the direction of rotation, because the rotary motor reverses direction without detectable changes in speed. This response to chemotactic signals is thought to be governed by interactions of small cytoplasmic proteins, CheY and CheZ, with the flagellar base (41,54,63,69). The third function of the flagellar apparatus, assembly of the flagellum, is thought to proceed by routing of the component proteins through the flagellar base into the hollow interior of the flagellum (21, 33, 50).The present understanding of bacterial flagellar structure rests largely on work on the peritrichously flagellated Escherichia coli and Salmonella typhimurium and the monoflagellated Caulobacter crescentus. Detergent solubilization of spheroplasts releases flagellar filaments that terminate in a set of basal rings, L/P and M/S (15). The basal rings have been purified together with the hook to make hook-basal body complexes (2,14,16,35,61,62). However, a number of proteins essential for flagellar function are absent from the hook-basal body complexes. These include MotA and MotB (two transmembrane proteins necessary for rotation) (13,60,67,68) and the switch complex (40, 48, 52, 69). The complete basal structure could also include other flagellar gene products whose function is presently unknown (32).Our effort has centered on the development of rapid-freeze * Corresponding author.procedures for the visualization of the total basal structure in situ and its relati...

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