Supramolecular organization of lysophosphatidylcholine-packaged gramicidin A′

Spisni, Alberto; Pasquali‐Ronchetti, I.; Casali, Emanuela; Lindner, Luisa; Cavatorta, P.; Masotti, Lanfranco; Urry, Dan W.

doi:10.1016/0005-2736(83)90186-4

Cited by 59 publications

(48 citation statements)

References 26 publications

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“…Dielectric relaxation studies at the same system were also interpreted on the basis of parallel-oriented neighboring channels [20]. Finally electron-microsopic investigations of GA in phospholipid micelles demonstrated the presence of a supramolecular organization of particles which were interpreted as hexamers of channels [42]. In the same study the presence of GA was found to convert the micelles into a vesicle-like bilayer structure.…”

Section: Discussionmentioning

confidence: 95%

“…The possibility of dimer-dimer interactions was first discussed by Urry [47] on the basis of his conformational studies. Direct evidence for a dimer aggregation has recently been obtained by different methods for gramicidin A incorporated into lysolecithin micelles [14,20,42]. We have examined the kinetics of channel formation in planar lipid membranes with our recently developed laser T-jump technique.…”

Section: Introductionmentioning

confidence: 98%

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Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel

Stark¹,

Strässle²,

Takácz³

1986

J. Membrain Biol.

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The kinetics of formation and dissociation of channels formed by gramicidin A and two analogues in planar lipid membranes was studied using a laser temperature-jump technique developed earlier [Brock, W., Stark, G., Jordan, P.C. (1981), Biophys. Chem. 13:329-348]. The time course of the electric current was found to agree with a single exponential term plus a linear drift. In case of gramicidin A the relaxation time was identical to that reported for V-jump experiments [Bamberg, E., Läuger, P. (1973), J. Membrane Biol. 11:177-194], which were interpreted on the basis of a dimerization reaction. The same results were obtained for gramicidin A and for chemically dimerized malonyl-bis-desformylgramicidin. It is therefore suggested that the dimerization represents a parallel association of two dimers to a tetramer. There is evidence that the tetramer, contrary to the presently favored dimer hypothesis, is the smallest conductance unit of an active gramicidin channel. An additional V-jump-induced relaxation process of considerably larger time constant is interpreted as a further aggregation of gramicidin dimers.

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Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 98%

Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel

Stark¹,

Strässle²,

Takácz³

1986

J. Membrain Biol.

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“…The gramicidin dimer has generally been thought to be the conducting chan nel, but aggregation of dimers has been shown to occur at high peptide densities (92,142). Several experimental findings such as the similarity between relaxation kinetics of gramicidin monomers and covalently linked gramicidin dimers in temperature-and voltage-jump experiments (148), the high sensitivity to UV light (31), the high dielectric permittivity (66), and the effects of Trp photolysis or radiolysis on channel formation rate (150) are difficult to explain without invoking a required cooperativity between dimers for conduction (150).…”

Section: Peptide Aggregationmentioning

confidence: 99%

The Use of Physical Methods in Determining Gramicidin Channel Structure and Function

Busath

1993

Annu. Rev. Physiol.

124

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The various details provided by physical methods have been integrated into a coherent picture of the cation transport process. The free energy profile describes simultaneously the thermodynamic and kinetic factors that govern conductance. Localization of ion binding sites near each end of the channel by NMR and X-ray crystallographic techniques demonstrates that there is an energy barrier separating the two ends. There is no a priori reason to suspect any barrier to ion entry into the channel, and recent molecular modeling computations confirm this intuition. Therefore, the channel is best described as a two-site, one-barrier channel. However, the movement of ions across the central barrier over a distance of 1.9 nm is really a multistep process best described as Brownian motion (even the short steps from one pair of carbonyls to the next is more diffusive than activated for ions as large as Na+), the entry step is probably best considered as a compound step requiring correction for interfacial polarization and diffusion limitation, the binding sites in the channel ought not be considered to be in equilibrium with the bath, and quasi-knock off behavior (binding of a second ion at the entry facilitates release of a first ion from the exit) is probably the rule at physiological permeant ion concentrations and higher. Progress will probably focus on channel kinetics. The channel backbone probably undergoes conformational changes as the ions pass which, according to solid state NMR results, may last long enough to provide the channel with a sort of memory and which may give rise to excess single channel noise. These conformational changes are further reflected in shifts in side chain positions which, in turn, may be partly responsible for changes in the single-channel lifetime, which appears to be exquisitely sensitive to side chain-lipid interactions. Reasonable explanations for the impermeance of divalent cations, anions, and medium-sized organic cations such as guanidinium have proven elusive at first, but it now appears that divalent cations bind water too tightly, anions bind water in an orientation that produces unfavorable contacts between water oxygens and peptide carbonyl oxygens at the channel entry, and iminium ions bind strongly to the flexible peptide carbonyls at the channel entry.

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“…From DSC [6], NMR, [7,8] X-ray diffraction and sucrose density centrifugation experiments, it could be concluded that this pentadecapeptide has a tendency to aggregate in the bilayer and that this aggregation is a prerequisite for HI1 phase formation. Interestingly, also for channel formation it appears that lateral aggregation of the peptide might be involved [10,18]. In the case of 18 : 1<./18 : 1 c PC, a lipid which has been studied most thoroughly [7][8][9], the HII phase is very rich in gramicidin (gramicidin/PC >/1 : 7, molar).…”

Section: Introductionmentioning

confidence: 99%

Conformational analysis of gramicidin-gramicidin interactions at the air/water interface suggests that gramicidin aggregates into tube-like structures similar as found in the gramicidin-induced hexagonal HII phase

Brasseur

Killian

Kruijff³

et al. 1987

Biochimica et Biophysica Acta (BBA) - Biomembranes

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The energetics of interaction and the type of aggregate structure in lateral assemblies of up to five gramicidin molecules in the fl6.3 helical conformation at the air/water interface was calculated using conformationai analysis procedures. It was found that within the aggregate two types of gramicidin interaction occur. One leading to a linear organization with a mean interaction energy between monomers of -6 kcal/mol and one in a perpendicular direction leading to a circularly organization with a lower mean interaction energy of -10 kcai/mol. Extrapolation towards larger gramicidin assemblies predicts that gramicidin itself could form tubular structures similar to those found in the gramicidin-induced H n phase. The tryptophans appear to play an essential role in the tubular organization of the gramicidin aggregate, since they determine the cone shape of the monomer and contribute to the structure of the monomer and oligomer by stacking interactions. These results, which are discussed in the light of experimental observations of gramicidin self-association in model membranes and the importance of the tryptophans for H n phase formation, further support the view (Killian, J.A. and De Kruijff, B. (1986) Chem. Phys. Lipids 40, 259-284) that gramicidin is a first example of a new class of hydrophobic polypeptides which can form cylindrical structures within the hydrophobic core of the membrane.

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Supramolecular organization of lysophosphatidylcholine-packaged gramicidin A′

Cited by 59 publications

References 26 publications

Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel

Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel

The Use of Physical Methods in Determining Gramicidin Channel Structure and Function

Conformational analysis of gramicidin-gramicidin interactions at the air/water interface suggests that gramicidin aggregates into tube-like structures similar as found in the gramicidin-induced hexagonal HII phase

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