The conformation of alamethicin

McMullen, A.I.; Marlborough, D. I.; Bayley, Peter M.

doi:10.1016/0014-5793(71)80369-1

Cited by 43 publications

(12 citation statements)

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“…Thus it is beyond doubt that the polypeptide which is monomeric in these solvents has indeed a rigid, a-helical, intrachenar, portion as has already been assumed on the basis of the solvent dependence of the two negative Cotton effects [24] and of a calculation of conformation [25]. In our investigations of the stability of this helical conformation we have obtained the CD data given in Table l .…”

Section: Solvent-dependence Of CD Spectramentioning

confidence: 70%

“…So far ideas on the molecular structure of these membrane pores have been based on molecular model building. There have been no spectroscopic investigations on alamethicin, with the exception of a CD study [23,24] and a 60-MHz 'H NMR spectrum [13]. Therefore we have been carrying out conformational investigations for some time using circular dichroism (CD) and 13C nuclear magnetic resonance (NMR) [5-71.…”

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confidence: 99%

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Conformational Changes of Alamethicin Induced by Solvent and Temperature

Jung

Dubischar

Leibfritz

1975

European Journal of Biochemistry

138

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I3C nuclear magnetic resonance (NMR) and circular dichroism (CD) have been used for studies on the conformation of alamethicin. The 13C NMR spectrum is assigned with the aid of signals of synthetic partial sequences and selective proton decoupling. The solvent and temperature-dependence of the I3C NMR spectra, TI measurements and the use of lanthanide-shift reagents allow the differentiation between the amino acids belonging to a rigid a-helical portion of the alamethicin sequence and those belonging to a more flexible part. The 13C NMR results are in agreement with results obtained from extended solvent and temperature-dependent CD studies which indicate a highly stabilized nonpolar and intrachenar a-helical part. The concentration-dependence of the CD spectrum of alamethicin in a nematic phase revealed aggregation phenomena which might simulate those observed in natural and synthetic membranes. After dissolving alamethicin in aqueous alcohol there is a time-dependence of the ellipticity of the Cotton effects showing a sort of memory effect on the mode of dissolution. Four different conformations can be characterized by CD spectra depending on the solvent and concentration. A model illustrating the dynamic conformations and aggregation phenomena within a membrane is proposed.Alamethicin, a membrane active peptide (antibiotic U-22324) can be isolated from the culture broth of the fungus Trichoderma viride [ 11. Biosynthetic studies [2] suggest a non-ribosomal enzymic mechanism for the synthesis of this unusual sequence. The verylipophilic polypeptide has only one ionized group in the form of a glutamine carboxylic group. In addition to a y-glutamyl peptide bond there are seven residues of a-aminoisobutyric acid which contribute to the characteristic properties of alamethicin. The primary structure of a cycle which comprises 17 amino acids was determined in 1970 [3] and confirmed by mass spectrometry [4].The peptide has strong lysing properties on membranes of Ehrlich ascites carcinoma cells and on erythrocytes. These appear within very narrow ranges Abbreviations. CD, circular dichroism; NMR, nuclear magnetic resonance; Aib, a-amino-isobutyric acid; Yb(fod)3, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato-ytterbium. .. show that alamethicin has a tendency to aggregate in neutral aequeous medium and that it might undergo hydrophobic interactions in phospholipids [12]. The tendency to form micelles at the lipid/water interface is also the basis of the models suggested so far to explain the molecular mechanism of the action of alamethicin on membranes [8,19]. The experiments exclude definitely a mobile carrier mechanism and point towards the formation of a hydrophilic ion-transporting "structure" in the membrane. So far ideas on the molecular structure of these membrane pores have been based on molecular model building. There have been no spectroscopic investigations on alamethicin, with the exception of a CD study [23,24] and a 60-MHz 'H NMR spectrum [13]. Therefore we have been carrying out conformatio...

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Section: Solvent-dependence Of CD Spectramentioning

confidence: 70%

mentioning

confidence: 99%

Conformational Changes of Alamethicin Induced by Solvent and Temperature

Jung

Dubischar

Leibfritz

1975

European Journal of Biochemistry

138

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“…McMullen, Marlborough and Bayley (1971) have also examined the conformational properties of alamethicin by optical rotary dispersion and circular dichroism in a variety of solvents. They found no effects of monovalent cations on the spectra, but a strong dependence on the solvent used.…”

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confidence: 99%

The nature of the voltage-dependent conductance induced by alamethicin in black lipid membranes

1973

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Summary. Alamethicin induces a conductance in black lipid films which increases exponentially with voltage. At low conductance the increase occurs in discrete steps which form a pattern of five levels, the second and third being most likely. The conductance of each level is directly proportional to salt concentration, inversely proportional to solution viscosity, and nearly independent of voltage.The probability distribution of the five steps is not a function of voltage, but as the voltage is increased, more levels begin to appear. These can be explained as superpositions of the original five, both in position and relative probability.This suggests that the five levels are associated with a physical entity which we call a pore. This point of view is confirmed by the following measurements. The kinetic response of the current to a voltage step is first order, and shows an exponential increase in rate of pore formation and an exponential decrease in rate of pore disappearance with voltage. If these rates are statistical, the number of pores should fluctuate about a voltage-dependent mean. High conductance current fluctuations are too large to be explained by fluctuation in the number of pores alone. But if fluctuations among the five levels are included, the magnitude of the fluctuations at high conductance is accurately predicted.Alamethicin adsorbs reversibly to the membrane surface, and the conductance at a fixed voltage depends on the ninth power of alamethicin concentration and on the fourth power of salt concentration, in the aqueous phase. In our bacterial phosphatidyl ethanolamine membranes, alamethicin added to one side of the membrane produces elevated conductance only when the voltage on that side is increased.

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“…Despite a number of physicochemical (13,14), conformational (15)(16)(17)(18), and chemical (17)(18)(19)(20)(21)(22) studies, the primary structure of ALA remains unknown. Currently, there are two proposed sequences: a cyclic (ALA-c) and an open chain (ALA-o) peptide structure (Fig.…”

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confidence: 99%

Synthesis of a 19-residue peptide with alamethicin-like activity.

Gisin¹,

Kobayashi²,

Hall³

1977

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

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This The peptide also affects the electrical properties of planar artificial lipid membranes in a unique and specific way: minute concentrations of ALA induce voltage-dependent conductances that mimic the action potential phenomena observed in nerve membranes. These effects were observed by Mueller and Rudin (6) and have been studied also by other groups (7-9). It is now generally believed that several ALA molecules aggregate in the membrane to form ion-conducting channels (8,(10)(11)(12).Despite a number of physicochemical (13, 14), conformational (15-18), and chemical (17-22) studies, the primary structure of ALA remains unknown. Currently, there are two proposed sequences: a cyclic (ALA-c) and an open chain (ALA-o) peptide structure (Fig. 1). The former, proposed by Payne et al. (19), has been confirmed by Ovchinnikov et al. (20), while the latter, proposed by Martin and Williams (21,22), found the support of the Jung group (17). The two proposals agree on a sequence of 15 consecutive residues (3-17 according to ALA-o numbering). In ALA-c the y-carboxyl group of Glu'8 is in amide linkage with Pro2 to form a cyclic structure. In

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The conformation of alamethicin

Cited by 43 publications

References 4 publications

Conformational Changes of Alamethicin Induced by Solvent and Temperature

Conformational Changes of Alamethicin Induced by Solvent and Temperature

The nature of the voltage-dependent conductance induced by alamethicin in black lipid membranes

Synthesis of a 19-residue peptide with alamethicin-like activity.

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