Images of a lipid bilayer at molecular resolution by scanning tunneling microscopy.

Smith, D. P. E.; Bryant, A. W.; Quate, C. F.; Rabe, Jürgen P.; Gerber, Ch.; Swalen, J. D.

doi:10.1073/pnas.84.4.969

Cited by 156 publications

(34 citation statements)

References 15 publications

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“…In addition to the lateral and vertical tip forces (37) which can have distorting effects on biological specimens, a number of other tip-surface interactions which produce spatial distortions have been recognized and include the following: tip shape, which acts to broaden convex structures and narrow concave structures (36); tip switching, which produces multiple images (11); tip-absorbed contaminants, which produce false images (16,19,36); capillary condensation of water vapor at ambient pressures, which reduces the height measurement and possibly deforms the surface of the specimen (40); and scanning speed and feedback gain, which may result in electrical interference and structural artifacts (36). Tunneling current in particular is sensitive to the conductive properties of the surface (13,20,27), and consequently, STM height errors from 20 to 70% have been reported (14). To overcome imaging problems associated with poor conductivity of biological material, Guckenberger et al (17) found that a small but sufficient conductivity from biological material can be induced at humidities of between 30 and 45%.…”

Section: Resultsmentioning

confidence: 99%

“…An important control for assessing the quality of topographical detail is to utilize structural landmarks or barrier heights for the positive identification of biomacromolecules in scanned images (15,25). Highly ordered biological surfaces (10,16,27,36,37), such as the paracrystalline proteinaceous structures examined in this study, provide mechanically rigid surfaces that contain useful landmark features for assessing image quality. From our TEM characterization of M. hungatei and its envelope structures, we could assess the quality of our STM and AFM images during scanning.…”

Section: Resultsmentioning

confidence: 99%

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Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

et al. 1993

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Methanospirllum hungatei GP1 possesses paracrystalline cell envelope components including end plugs and a sheath formed from stacked hoops. Both negative-stain transmission electron microscopy (TEM) and scanning tunneling microscopy (STM) distinguished the 2.8-nm repeat on the outer surface of the sheath, while negative-stain TEM alone demonstrated this repeat around the outer circumference of individual hoops. Thin sections revealed a wave-like outer sheath surface, while STM showed the presence of deep grooves that precisely defined the hoop-to-hoop boundaries at the waveform nodes. Atomic force microscopy of sheath tubes containing entrapped end plugs emphasized the end plug structure, suggesting that the sheath was malleable enough to collapse over the end plugs and deform to mimic the shape of the underlying structure. High-resolution atomic force microscopy has revised the former idea of end plug structure so that we believe each plug consists of at least four discs, each of which is -3.5 nm thick. Pt shadow TEM and STM both demonstrated the 14-nm hexagonal, particulate surface of an end plug, and STM showed the constituent particles to be lobed structures with numerous smaller projections, presumably corresponding to the molecular folding of the particle.All current techniques for ultrahigh resolution of biomolecular structure have inherent drawbacks. For example, not only does transmission electron microscopy (TEM) usually require heavy metal contrasting agents, it also produces high energy loads and high vacuums on the specimen. Only in exceptional cases, such as the purple membrane of Halobacterium spp. (18), have molecular folding data been obtained. The inception of scanning tunneling microscopy (STM) (7) and atomic force microscopy (AFM) (6) has certainly made the atomic resolution of hard, inanimate surfaces feasible, and there is a good possibility that this same resolution can be approached in biology. STM and AFM are currently being used on a number of biostructures and their constituent biopolymers, but they are still relatively new techniques in structural biology, and submolecular resolution must be interpreted with caution since biomaterials are loosely bonded and easily deformable. Specimens must be chosen with care, and close attention must be paid to the possibility of induced artifacts. It is best to take a multitechnique approach which combines high-resolution methodologies based on different principles; uniformity of high-resolution detail from each ensures accuracy of interpretation. Using this rationale, we have combined TEM, STM, and AFM to study paracrystalline surfaces possessed by the archaeobacterium Methanospirillum hungatei.STM and AFM rely on the raster scanning of a fine-tip probe over a surface, with piezoelectric ceramics to control movement to within subnanometer distances, which forms a topographical three-dimensional image of the specimen. In STM, the vertical tip displacement during scanning is depen-* Corresponding author. dent on the tunneling current between the pen...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

et al. 1993

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“…At present, high resolution STM images of a film of phospholipid in solution can be acquired for a monolayer only. However, molecular resolution STM images of a phospholipid bilayer supported at a conductive surface in air have already been reported (28)(29)(30). With further methodological improvements, imaging of the supported bilayer in a solution should also be possible in the future.…”

mentioning

confidence: 99%

Direct visualization of the alamethicin pore formed in a planar phospholipid matrix

Pieta

Mirza

Lipkowski

2012

Proc. Natl. Acad. Sci. U.S.A.

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We present direct visualization of pores formed by alamethicin (Alm) in a matrix of phospholipids using electrochemical scanning tunneling microscopy (EC-STM). High-resolution EC-STM images show individual peptide molecules forming channels. The channels are not dispersed randomly in the monolayer but agglomerate forming 2D nanocrystals with a hexagonal lattice in which the average channel-channel distance is 1.90 ± 0.1 nm. The STM images suggest that each Alm is shared between the two adjacent channels. Every channel consists of six Alm molecules. Three or four of these molecules have the hydrophilic group oriented toward the center of the channel allowing for water column formation inside the channel. The dimensions of the central pore in the images are consistent with the dimension of the water column in a model of hexameric pore proposed in the literature. The images obtained in this work validate the barrel-stave model of the pore formed in phospholipid membranes by amphiphatic peptides. They also provide direct evidence for cluster formation by such pores.antimicrobial | interface | Langmuir-Blodgett

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“…29 The uneven coverage of the hydrophobic surface and the formation of multilamellar islands make this technique unsuitable for exact bilayer partitioning studies where a well-defined system is needed. The Langmuir-Blodgett technique 30 produced a phospholipid monolayer on the surface of gold-coated plates with covalently attached octadecyl chains. 31,32 The obtained monolayer was uniform and stable in both dry and rehydrated forms.…”

Section: Supported Monolayer Systemsmentioning

confidence: 99%

Drug-Membrane Interactions Studied in Phospholipid Monolayers Adsorbed on Nonporous Alkylated Microspheres

et al. 2007

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Characterization of interactions with phospholipids is an integral part of the in vitro profiling of drug candidates because of the roles the interactions play in tissue accumulation and passive diffusion. Currently used test systems may inadequately emulate the bilayer core solvation properties (immobilized artificial membranes [IAM]), suffer from potentially slow transport of some chemicals (liposomes in free or immobilized forms), and require a tedious separation (if used for free liposomes). Here the authors introduce a well-defined system overcoming these drawbacks: nonporous octadecylsilica particles coated with a self-assembled phospholipid monolayer. The coating mimics the structure of the headgroup region, as well as the thickness and properties of the hydrocarbon core, more closely than IAM. The monolayer has a similar transition temperature pattern as the corresponding bilayer. The particles can be separated by filtration or a mild centrifugation. The partitioning equilibria of 81 tested chemicals were dissected into the headgroup and core contributions, the latter using the alkane/water partition coefficients. The deconvolution allowed a successful prediction of the bilayer/water partition coefficients with the standard deviation of 0.26 log units. The plate-friendly assay is suitable for high-throughput profiling of drug candidates without sacrificing the quality of analysis or details of the drug-phospholipid interactions.

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Images of a lipid bilayer at molecular resolution by scanning tunneling microscopy.

Cited by 156 publications

References 15 publications

Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

Direct visualization of the alamethicin pore formed in a planar phospholipid matrix

Drug-Membrane Interactions Studied in Phospholipid Monolayers Adsorbed on Nonporous Alkylated Microspheres

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