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Conformation of alamethicin in phospholipid vesicles: implications for insertion models.

Authors
  • Cascio, M
  • Wallace, B A
Type
Published Article
Journal
Proteins
Publication Date
Jan 01, 1988
Volume
4
Issue
2
Pages
89–98
Identifiers
PMID: 3227017
Source
Medline
License
Unknown

Abstract

The secondary structure of alamethicin, a membrane channel-forming polypeptide, has been examined by circular dichroism spectroscopy to determine the relationship of its conformation in organic solution to its conformation in a membrane-bound state. The spectrum of alamethicin in small unilamellar dimyristoyl phosphatidylcholine vesicles is significantly different from its spectrum in 10% methanol/acetonitrile, the solvent from which it was crystallized (Fox and Richards: Nature 300:325-330, 1982), as well as its spectrum in methanol, the solvent in which NMR studies have been done (Banerjee and Chan: Biochemistry 22:3709-3713, 1983). This suggests that structural models based on studies of the molecule in organic solvents may not be entirely appropriate for the membrane-bound state. To distinguish between different models for channel formation and insertion, two different methods were used to associate the alamethicin with vesicles; in addition, the effect of oligomerization on the conformation of the membrane-bound state was investigated. These studies are consistent with a modified insertion model in which alamethicin monomers, dimers, or trimers associate with the bilayer and then spontaneously oligomerize to form a prechannel with a higher helix content. This aggregate could then "open" upon application of an appropriate gating transmembrane potential.

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