Interactions of tryptophan, tryptophan peptides, and tryptophan alkyl esters at curved membrane interfaces

Wei Liu, Martin Caffrey

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Motivated by ongoing efforts to understand the mechanism of membrane protein crystallogenesis and transport in the lipidic cubic phase, the nature of the interaction between tryptophan and the bilayer/aqueous interface of the cubic phase has been investigated. The association was quantified by partitioning measurements that enabled the free energy of interaction to be determined. Temperature-dependent partitioning was used to parse the association free energy change into its enthalpic and entropic components. As has been observed with tryptophan derivatives interacting with glycerophospholipid bilayers in vesicles, tryptophan partitioning in the cubic phase is enthalpy driven. This is in contrast to partitioning into apolar solvents, which exhibits the classic hydrophobic effect whose hallmark is a favorable entropy change. These results with tryptophan are somewhat surprising given the simplicity, homogeneity, and curvature of the interface that prevails in the case of the cubic phase. Nevertheless, the interaction between tryptophan and the mesophase is very slight as revealed by its low partition coefficient. Additional evidence in support of the interaction was obtained by electronic absorption and fluorescence spectroscopy and fluorescence quenching. Partitioning proved insensitive to the lipid composition of the membrane, examined by doping with glycerophospholipids. However, the interaction could be manipulated in meaningful ways by the inclusion in the aqueous medium of salt, glycerol, or urea. The effects seen with tryptophan were amplified rationally when measurements were repeated using tryptophan alkyl esters and with tryptophan peptides of increasing length. These findings are interpreted in the context of the insertion, folding, and function of proteins in membranes.

Original languageEnglish (US)
Pages (from-to)11713-11726
Number of pages14
JournalBiochemistry
Volume45
Issue number39
DOIs
StatePublished - Oct 3 2006
Externally publishedYes

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Tryptophan
Esters
Membranes
Peptides
Glycerophospholipids
Free energy
Association reactions
Free Association
Membrane Transport Proteins
tryptophyltryptophan
Fluorescence Spectrometry
Protein Folding
Fluorescence spectroscopy
Entropy
Membrane Lipids
Absorption spectroscopy
Glycerol
Urea
Enthalpy
Quenching

ASJC Scopus subject areas

  • Biochemistry

Cite this

Interactions of tryptophan, tryptophan peptides, and tryptophan alkyl esters at curved membrane interfaces. / Liu, Wei; Caffrey, Martin.

In: Biochemistry, Vol. 45, No. 39, 03.10.2006, p. 11713-11726.

Research output: Contribution to journalArticle

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