Controlled ionic condensation at the surface of a native extremophile membrane.
Nanoscale 2:2 (2010) 222-229
Abstract:
At the nanoscale level biological membranes present a complex interface with the solvent. The functional dynamics and relative flexibility of membrane components together with the presence of specific ionic effects can combine to create exciting new phenomena that challenge traditional theories such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory or models interpreting the role of ions in terms of their ability to structure water (structure making/breaking). Here we investigate ionic effects at the surface of a highly charged extremophile membrane composed of a proton pump (bacteriorhodopsin) and archaeal lipids naturally assembled into a 2D crystal. Using amplitude-modulation atomic force microscopy (AM-AFM) in solution, we obtained sub-molecular resolution images of ion-induced surface restructuring of the membrane. We demonstrate the presence of a stiff cationic layer condensed at its extracellular surface. This layer cannot be explained by traditional continuum theories. Dynamic force spectroscopy experiments suggest that it is produced by electrostatic correlation mediated by a Manning-type condensation of ions. In contrast, the cytoplasmic surface is dominated by short-range repulsive hydration forces. These findings are relevant to archaeal bioenergetics and halophilic adaptation. Importantly, they present experimental evidence of a natural system that locally controls its interactions with the surrounding medium and challenges our current understanding of biological interfaces.AFM observation of single membrane proteins and its application to nano biodevices
IEEJ Transactions on Electronics, Information and Systems 130:10 (2010)
Abstract:
Recent progress on nanotechnology including nanostructure fabrication and nanometer-scale measurement techniques, and work on biomolecules whose size is equivalent to that covered by nanotechnology, are expected to result in the creation of a new research field called nano-bio science. This article introduces our recent work on the observation of single biomolecule; reconstituted a receptor protein into an artificial lipid membrane using an atomic force microscope (AFM). An AFM is a measurement tool that enables us to observe nanometer-scale objects in a liquid environment. We also examine the orientation of the proteins in proteoliposomes with the dynamic light scattering technique (DLS). Most receptor proteins have orientations in molecules, for example the extracellular and intracellular domains. Determining the protein orientation is essential for nano-biodevice fabrication if we wish to utilize the protein's function. We also introduce our recent attempt to realize a nano-bio device; a very small device obtaining and utilizing biological functions; using our state-of-the-art nanofabrication technique and a technique for handling receptor proteins. Thus, by combining nanotechnology and biotechnology to realize nano-biodevices, we can produce ultra-small biological sensors for implantation. Further improvements are expected. © 2010 The Institute of Electrical Engineers of Japan.Molecular Dynamics Study of CNT Nanopores Embedded in Lipid Bilayers
BIOPHYSICAL JOURNAL 98:3 (2010) 757A-757A
Lateral coupling and cooperative dynamics in the function of the native membrane protein bacteriorhodopsin
Soft Matter 5:24 (2009) 4899-4904
Abstract:
Membrane proteins are laterally coupled to the surrounding cell membrane through complex interactions that can modulate their function. Here, we directly observe and quantify the dynamics of functioning bacteriorhodopsin (bR) in its native membrane, a crystalline aggregate of bR trimers. We show that much of a monomer's isomerization energy is mechanically redistributed into the membrane, producing cooperative activity within the trimer while simultaneously generating functionally relevant long-range lateral pressure waves. Our results provide evidence of coordinated short and long-range effects in the cell membrane. © 2009 The Royal Society of Chemistry.Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy.
J Struct Biol 167:2 (2009) 153-158