Biological Physics
Supramolecular Structures Lab
Lösche Group
Research
Tethered bilayer lipid membranes (tBLMs) for biomedical research
Physiological bilayer membranes – fluid leaflets self-assembled by non-covalent interactions and a mere 5 nanometers thin – are ubiquitously used in biological cells but much to delicate to use in practical applications. While a great deal of fundamental research has been achieved with model systems such as "Black Lipid Membranes", i.e. freely suspended bilayers between two semi-infinite buffer compartments, these are entirely unsuitable if it comes to long-term experiments, be it systematic screening, observations over extended periods or technological applications. Also, such BLMs are not suitable for high-res structural investigations, because they're so small in lateral extension (~ 10-2 mm2).
Self-assembled protein-lipid membranes may serve as functional interface architectures in applications that range from biosensorics to pharmacological screening.
In principle, there are established techniques to form, or to transfer, bilayer membranes on solid supports, thus addressing both the stability and the size limitations. However, membranes in contact with solid substrates loose their intrinsic dynamics – both in-plane and, of course, out-of-plane – due to the interaction of the constituent lipids with the solid surface. Also, proteins which one might want to incorporate into the reconstituted membrane for functionalization, tend to denature (unfold from their specific three-dimensional structure required for protein function) at the surface. We have developed specific molecular surface architectures, substrate-supported tethered bilayer lipid membranes (tBLMs), in which the 50 Å thick bilayer membrane is adsorbed to a solid surface via a hydrated chemical tether. The ingredients in this work were a dedicated synthetic chemistry (mainly performed by David Vanderah at NIST-CSTL), an unconventional preparation procedure for bilayer completion (first introduced by the Cornell group), electrochemical impedance spectroscopy (the EIS technique has been brought to us by Gintaras Valincius of the Biochemistry Institute in Vilnius, Lithuania) for facile system optimization, and neutron reflectometry (NR) for the high-res structural assessment of the resulting architecture.
Our workhorses: X-ray and neutron scattering techniques are used to characterize the molecular structure of tBLMs, and electrochemical characterization is used to assess the defect density of the membrane.
The result has been an optimized experimental system, easy and reproducibly to prepare in simple bake-and-shake sample preps, the we now use in various applications within a multitude of collaborations: Molecular-scale characterization of amyloid-membrane interactions (with Jim Hall and Charly Glebe at UC Irvine), reconstitution of toxin pores – S. aureus α-hemolysin or B. anthracis PA63 – for their direct structural characterization in the membrane environment (with John Kasianowicz at NIST-EEEL), or the characterization of conformational changes of toxins, such as diphtheria and cholera toxins, as they hit the membrane surface (with Mike Kent at Sandia). In all cases, the use of tBLMs lets us explore dimensions in biomedical research that have not previously been accessible.
Research topics
Alzheimer's peptide amyloid β: Mechanisms of Aβ toxicity. More...
Membrane incorporation of the protein toxin pore α-hemolysin. More...
tBLM optimization at the NIST Center for Neutron Research. More...