Fluctuations of barrier structure in ionic channels

Läuger, P.; Stephan, Wolfgang; Frehland, E.

doi:10.1016/0005-2736(80)90299-0

Cited by 104 publications

(62 citation statements)

References 25 publications

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“…We note that the distinction between channel and transporter becomes fuzzy if the pore is so narrow that protein dynamics is required to permit diffusive ion movement. Such channel-transporter chimeras were envisioned theoretically by Läuger et al many years ago (29).…”

Section: Discussionmentioning

confidence: 99%

Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger

Jayaram

Accardi

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

148

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The CLC family of Cl ؊ -transporting proteins includes both Cl ؊ channels and Cl ؊ /H ؉ exchange transporters. CLC-ec1, a structurally known bacterial homolog of the transporter subclass, exchanges two Cl ؊ ions per proton with strict, obligatory stoichiometry. Point mutations at two residues, Glu 148 and Tyr 445 , are known to impair H ؉ movement while preserving Cl ؊ transport. In the x-ray crystal structure of CLC-ec1, these residues form putative ''gates'' flanking an ion-binding region. In mutants with both of the gate-forming side chains reduced in size, H ؉ transport is abolished, and unitary Cl ؊ transport rates are greatly increased, well above values expected for transporter mechanisms. Cl ؊ transport rates increase as side-chain volume at these positions is decreased. The crystal structure of a doubly ungated mutant shows a narrow conduit traversing the entire protein transmembrane width. These characteristics suggest that Cl ؊ flux through uncoupled, ungated CLC-ec1 occurs via a channel-like electrodiffusion mechanism rather than an alternating-exposure conformational cycle that has been rendered proton-independent by the gate mutations.

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Section: Discussionmentioning

confidence: 99%

Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger

Jayaram

Accardi

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

148

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“…Finally, classification in terms of channels and carriers may not have fundamental significance with regard to energy-transducing devices. Ion translocation through channels (i.e., gated pores) if limited by conformational transitions could exhibit features, such as lowered flux, characteristic of carriers (24). Physiologically important carriers are thought to be pores "closed at one end by a molecular machine that accomplishes the coupled translocation steps over a short distance" (15).…”

Section: Discussionmentioning

confidence: 99%

Ion selectivity of the Vibrio alginolyticus flagellar motor

1990

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The marine bacterium, Vibrio alginolyticus, normally requires sodium for motility. We found that lithium will substitute for sodium. In neutral pH buffers, the membrane potential and swimming speed of glycolyzing bacteria reached maximal values as sodium or lithium concentration was increased. While the maximal potentials obtained in the two cations were comparable, the maximal swimming speed was substantially lower in lithium. Over a wide range of sodium concentration, the bacteria maintained an invariant sodium electrochemical potential as determined by membrane potential and intracellular sodium measurements. Over this range the increase of swimming speed took Michaelis-Menten form. Artificial energization of swimming motility required imposition of a voltage difference in concert with a sodium pulse. The cation selectivity and concentration dependence exhibited by the motile apparatus depended on the viscosity of the medium. In high-viscosity media, swimming speeds were relatively independent of either ion type or concentration. These facts parallel and extend observations of the swimming behavior of bacteria propelled by proton-powered flagella. In particular, they show that ion transfers limit unloaded motor speed in this bacterium and imply that the coupling between ion transfers and force generation must be fairly tight.The rotation of bacterial flagella (6) (25). The role of proton transfers in limiting motor speed has been probed by study of hydrogen isotope effects. Isotope effects were absent during tethered cell rotation (9, 18) but prominent during rapid rotation of flagellar bundles in free-swimming cells (9,25).An increasing number of bacterial species are being identified in which flagellar rotation depends on sodium gradients (4,11,12,16,17,33,34). Identification, upon comparison with the proton motors, of the changes in machinery and mechanism that provide the basis for the sodium dependence should yield valuable clues about the coupling between ion transfers and force generation. We began work on Vibrio alginolyticus guided by this consideration. We chose V. alginolyticus since it (i) has well-characterized physiology (35, 36), (ii) exhibits good motility at neutral pH, at which proton pumps maintain the membrane potential independently of sodium (36)

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“…A simple investigation proves that in the archetypal one-site model of Läuger, [11], the dependence of the flux on the fluctuations' transition rate is monotonic for both the cases of transitions between the potential conformations which are discussed below. Thus, searching for more complex behaviour, one should analyze channels with multiple binding sites.…”

Section: Resultsmentioning

confidence: 87%

“…Otherwise, the form of the potential during the very escape event is not well defined [11,12]. The internal motions in proteins occur on time scales from several picoseconds to seconds or even minutes, while t r is estimated to be of the order of 1 ps.…”

Section: Methodsmentioning

confidence: 99%

Kinetic models for stochastically modified ionic channels

Wozinski

Iwaniszewski

2008

Cellular and Molecular Biology Letters

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Ionic channels form pores in biomembranes. These pores are large macromolecular structures. Due to thermal fluctuations of countless degrees-offreedom of the biomembrane material, the actual form of the pores is permanently subject to modification. Furthermore, the arrival of an ion at the binding site can change this form by repolarizing the surrounding aminoacids. In any case the variations of the pore structure are stochastic. In this paper, we discuss the effect of such modifications on the channel conductivity. Applying a simple kinetic description, we show that stochastic variations in channel properties can significantly alter the ionic current, even leading to its substantial increase or decrease for the specific matching of some time-scales of the system.

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Fluctuations of barrier structure in ionic channels

Cited by 104 publications

References 25 publications

Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger

Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger

Ion selectivity of the Vibrio alginolyticus flagellar motor

Kinetic models for stochastically modified ionic channels

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Fluctuations of barrier structure in ionic channels

Cited by 104 publications

References 25 publications

Ion permeation through a Cl − -selective channel designed from a CLC Cl − /H + exchanger

Ion permeation through a Cl − -selective channel designed from a CLC Cl − /H + exchanger

Ion selectivity of the Vibrio alginolyticus flagellar motor

Kinetic models for stochastically modified ionic channels

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Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger

Ion permeation through a Cl ⁻ -selective channel designed from a CLC Cl ⁻ /H ⁺ exchanger