Histidine-Tagged Amphiphiles for the Reversible Formation of Lipid Bilayer Aggregates on Chelator-Functionalized Gold Surfaces

A new strategy for the reversible formation of supported lipid bilayers is introduced. It uses an extension of immobilized metal ion affinity chromatog. technol., which depends on the reversible formation of complexes between metal ion binding chelator groups and oligohistidines. Lipid layers contg. hexahistidine-derivatized amphiphiles (His-lipids) are anchored to a self-assembled monolayer (SAM) contg. synthetic chelator thioalkanes (CTA). The control over the d. of anchor sites on the substrate and over the surface wetting properties leads to a high degree of flexibility in the design of extra free space between the substrate and the lipid layer for the reconstitution of proteins. His-lipids can be used to anchor planar lipid layers or layers of intact lipid vesicles to CTA SAMs. The form of the lipid layers (planar bilayer or vesicles) is detd. by the charge on the lipids and the ionic strength of the buffer soln. used. Surface plasmon resonance is used to monitor the formation of lipid layers. The synthesis of the His-lipid and the characterization of its monolayer layer forming and binding properties on a Langmuir trough are also described. [on SciFinder (R)]

A new class of thiolipids for the attachment of lipid bilayers on gold surfaces

Claus Duschl, Horst Vogel

A new class of lipid mols. is synthesized, based on two dipalmitoylphosphatidic mols., each extended at the lipid phosphate by a hydrophilic spacer chain of ethoxy groups of variable length, which are then coupled as a bilipid via a terminal disulfide group at the hydrophilic spacer. These anchor-bearing "thiolipids" can attach to gold substrates by forming stable gold-sulfur bonds. In this way, the authors can couple lipid bilayers to gold surfaces, with the possibility of preserving a water layer between the support and the first monolayer. The thiolipid mols. are characterized on a Langmuir film balance using fluorescence microscopy. The mol. areas of the thiolipids on the water surface are 80-90 .ANG.2 at a fully compressed state. The thiolipid monolayers show a typical first-order phase transition on the water surface with regular, starlike domains. The formation of thiolipid-attached mono- and bilayers on gold surfaces was studied by surface plasmon resonance (SPR), impedance measurements, and cyclic voltammetry. Four different supported membrane systems are studied in detail: (1) pure thiolipid layers; (2) mixed lipid bilayers contg. a first pure thiolipid monolayer and a second one of conventional phospholipids; (3) bilayers, where the first gold-attached monolayer is composed of a mixt. of thio- and conventional phospholipids with another second phospholipid layer on top; (4) monolayers of pure 1-hexadecanethiol and layers with a second phospholipid film on top of the 1-hexadecanethiol. The electrochem. expts. reveal elec. blocking layers for all lipid systems investigated with specific resistances of 104-105 W cm2. The capacitance values for pure thiolipid bilayers are in the range of 0.5-0.7 mF/cm2 for the pure thiolipid bilayers and 0.7-0.8 mF/cm2 for the mixed thiolipid/phospholipid bilayers, which is comparable to the values found for unsupported, so-called black lipid membranes. SPR measurements confirm qual. the results of the electrochem. expts. [on SciFinder (R)]

1994

Sulfur-bearing lipids for the covalent attachment of supported lipid bilayers to gold surfaces: a detailed characterization and analysis

Jacques Dubochet, Claus Duschl, Martha Liley, Henning Paul-Julius Stahlberg, Horst Vogel, Shaik Mohammed Zakeeruddin

In a recent paper, a new class of synthetic lipids, which self-assemble to form monolayers on gold surfaces, was introduced. The addn. of a monolayer of phospholipids to these layers results in robust supported lipid bilayers designed to reconstitute transmembrane proteins. This paper presents a detailed characterization of the monolayers and bilayers formed by these lipids and assesses their ability for the incorporation of membrane-spanning proteins. Film balance methods, electron microscopy, surface plasmon resonance, Fourier transform IR measurements and Raman spectroscopy show the feasibility of this concept. However, further modifications to improve the thiolipids are necessary. A new strategy for the formation of laterally structured supported lipid bilayers is discussed and initial results are presented. [on SciFinder (R)]

1996

A new class of thiolipids for the attachment of lipid bilayers on gold surfaces

Claus Duschl, Horst Vogel

1994