The electric unit size of thylakoid membranes

Schönknecht, Gerald; Althoff, Gerd; Junge, Wolfgang

doi:10.1016/0014-5793(90)80810-6

Cited by 23 publications

(19 citation statements)

References 13 publications

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“…Besides helix‐helix association in a parallel fashion, many small peptides can assemble into linear dimers that span the length of a bilayer . For example, the functional state of gramicidin A corresponds to a helical dimer arranged in a head‐to‐head manner .…”

Section: Initiation and Probing Methodsmentioning

confidence: 99%

Kinetics of peptide folding in lipid membranes

2015

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Despite our extensive understanding of water-soluble protein folding kinetics, much less is known about the folding dynamics and mechanisms of membrane proteins. However, recent studies have shown that for relatively simple systems, such as peptides that form a transmembrane α-helix, helical dimer, or helix-turn-helix, it is possible to assess the kinetics of several important steps, including peptide binding to the membrane from aqueous solution, peptide folding on the membrane surface, helix insertion into the membrane, and helix-helix association inside the membrane. Herein, we provide a brief review of these studies and also suggest new initiation and probing methods that could lead to improved temporal and structural resolution in future experiments.

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Section: Initiation and Probing Methodsmentioning

confidence: 99%

Kinetics of peptide folding in lipid membranes

2015

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“…The maximum number of channels formed by gramicidin per thylakoid was calculated from the known number of dimers added (6.6 pM gramicidin corresponds to 100 channels per thylakoid vesicle). We estimated 1 ϫ 10 9 chloroplasts per mg of chlorophyll and assumed one thylakoid vesicle per chloroplast (23). It is important to note that these assumptions do not enter into the final conclusions of our study, because potential translocase conductivities are discussed in relation to the conductance of gramicidin channels that are calibrated by using the same assumed numbers.…”

Section: Methodsmentioning

confidence: 99%

Energy-transducing thylakoid membranes remain highly impermeable to ions during protein translocation

Teter

Theg

1998

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

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We investigated the operation of a posttranslational protein translocation pathway to determine whether ions are excluded from the translocase during protein transport. The membrane capacitance during protein translocation across chloroplast thylakoid membranes was monitored via electric-field-indicating carotenoid electrochromic bandshift measurements. Evidence is presented that shows that the membrane ion conductance is not increased during the complete cycle of binding, transport, and substrate release by the ⌬pH-dependent translocase; i.e., the membrane remains iontight during protein translocation. We further demonstrate that a synthetic targeting peptide that directs proteins across this membrane does not gate translocation pores. We conclude that protein transport across the thylakoid membrane does not compromise its ability to maintain ion gradients and is, thus, unlikely to affect its functions in energy transduction.Although a number of experiments indicate that many proteins traverse membranes through aqueous pores, passing from N terminus to C terminus in an extended conformation (1), it is becoming increasingly apparent that some translocases are capable of transporting proteins possessing a variety of structures. Mitochondria and bacterial membrane transporters can accommodate branched (2) and disulfide-bridged (3) proteins, respectively. Chloroplasts have recently been shown to import fully folded polypeptides (4, 5) and the import of oligomerized proteins and even gold particles has been demonstrated in peroxisomes (6-8). In addition, it has been shown for several translocases that the same machinery mediates the transport of both soluble and integral membrane proteins (9, 10). These observations indicate that protein translocases are dynamic and versatile in their ability to transport substrates with different structures into diverse environments. Because proteins have irregular surfaces and translocators have broad specificities, the question arises as to whether ion leakage accompanies protein transport through a pore, thereby compromising the ion permeability barrier of the membrane. This issue has been examined by using artificially induced membrane-spanning translocation intermediates, with some researchers describing an attendant ion leakage and others reporting no accompanying change in ion permeability (11)(12)(13). In addition, the presumed interactions of different targeting peptides with translocators have been reported to alter ion flux, in some cases by opening ion-conducting channels and in other cases by transiently blocking ion movement through active channels (14 -18). In one such report, substratedependent proton flux through the bacterial protein secretion machinery was observed, albeit only when some of the translocon components were overproduced (19). In the present study, we used a native precursor to examine the total ion conductance of the energy-transducing chloroplast thylakoid membrane during uninterrupted translocation cycles of a protein transporter. MATERIAL...

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“…The whole membrane system inside a chloroplast can be unfolded into one large spherical bleb (28). Also, a single dimer of the powerful ionophore gramicidin per more than 10 7 chlorophyll molecules accelerates the decay of the transmembrane voltage (30). In other words, this intricately folded system seems to form a single, simply connected sheet (in mathematical terms) such that more than 10 4 electron transport chains and ATP synthase molecules are electrically coupled with one another.…”

Section: Architecture Of the Coupling Membranementioning

confidence: 99%

ATP Synthase

Junge

Nelson

2015

Annu. Rev. Biochem.

309

251

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Oxygenic photosynthesis is the principal converter of sunlight into chemical energy. Cyanobacteria and plants provide aerobic life with oxygen, food, fuel, fibers, and platform chemicals. Four multisubunit membrane proteins are involved: photosystem I (PSI), photosystem II (PSII), cytochrome b6f (cyt b6f), and ATP synthase (FOF1). ATP synthase is likewise a key enzyme of cell respiration. Over three billion years, the basic machinery of oxygenic photosynthesis and respiration has been perfected to minimize wasteful reactions. The proton-driven ATP synthase is embedded in a proton tight-coupling membrane. It is composed of two rotary motors/generators, FO and F1, which do not slip against each other. The proton-driven FO and the ATP-synthesizing F1 are coupled via elastic torque transmission. Elastic transmission decouples the two motors in kinetic detail but keeps them perfectly coupled in thermodynamic equilibrium and (time-averaged) under steady turnover. Elastic transmission enables operation with different gear ratios in different organisms.

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The electric unit size of thylakoid membranes

Cited by 23 publications

References 13 publications

Kinetics of peptide folding in lipid membranes

Kinetics of peptide folding in lipid membranes

Energy-transducing thylakoid membranes remain highly impermeable to ions during protein translocation

ATP Synthase

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