Single-Molecule Force Spectroscopy on Xanthan by AFM

Li, Hongbin; Rief, Matthias; Oesterhelt, Filipp; Gaub, Hermann E.

doi:10.1002/(sici)1521-4095(199803)10:4<316::aid-adma316>3.3.co;2-1

Cited by 75 publications

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“…A drop of these solutions was placed onto glass coverslips for drying followed by extensive rinsing. This procedure leaves a layer of polysaccharide molecules tightly adsorbed to the glass surface (7). The measurements were carried out in water or in PBS.…”

Section: Methodsmentioning

confidence: 99%

“…Our experiments enhance the ability of single-molecule force spectroscopy to make high-resolution measurements of the conformations of single polysaccharide molecules under a stretching force, making an important addition to polysaccharide spectroscopy. S ingle molecule force spectroscopy has become an important tool to examine the conformations of proteins and polysaccharide molecules under a stretching force (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Recent experiments have demonstrated that a force field can trigger conformational changes in these molecules that cannot be observed by traditional NMR or x-ray crystallographic techniques.…”

mentioning

confidence: 99%

“…Recent experiments have demonstrated that a force field can trigger conformational changes in these molecules that cannot be observed by traditional NMR or x-ray crystallographic techniques. Force spectroscopy involves measuring the force required to extend a molecule by a certain amount (2)(3)(4)(5)(6)(7)(8)(9)(10). The data are compiled into a forceextension relationship that gives a characteristic fingerprint for the conformational transitions of the molecule under study.…”

mentioning

confidence: 99%

“…In the most typical atomic force microscopy (AFM) experiment, a single molecule adsorbed between a substrate and the cantilever tip is extended vertically at a constant rate while the resulting force is measured (2)(3)(4)(5)(6)(7)(8)(9)(10). Although it may seem that these experiments can be completed equally by controlling either the extension or the force applied to the molecule, these two modes can yield quite different results (e.g., see ref.…”

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confidence: 99%

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Chair-boat transitions in single polysaccharide molecules observed with force-ramp AFM

Marszałek

Oberhauser

et al. 2002

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

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136

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Under a stretching force, the sugar ring of polysaccharide molecules switches from the chair to the boat-like or inverted chair conformation. This conformational change can be observed by stretching single polysaccharide molecules with an atomic force microscope. In those early experiments, the molecules were stretched at a constant rate while the resulting force changed over wide ranges. However, because the rings undergo force-dependent transitions, an experimental arrangement where the force is the free variable introduces an undesirable level of complexity in the results. Here we demonstrate the use of force-ramp atomic force microscopy to capture the conformational changes in single polysaccharide molecules. Force-ramp atomic force microscopy readily captures the ring transitions under conditions where the entropic elasticity of the molecule is separated from its conformational transitions, enabling a quantitative analysis of the data with a simple two-state model. This analysis directly provides the physico-chemical characteristics of the ring transitions such as the width of the energy barrier, the relative energy of the conformers, and their enthalpic elasticity. Our experiments enhance the ability of single-molecule force spectroscopy to make high-resolution measurements of the conformations of single polysaccharide molecules under a stretching force, making an important addition to polysaccharide spectroscopy. S ingle molecule force spectroscopy has become an important tool to examine the conformations of proteins and polysaccharide molecules under a stretching force (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Recent experiments have demonstrated that a force field can trigger conformational changes in these molecules that cannot be observed by traditional NMR or x-ray crystallographic techniques. Force spectroscopy involves measuring the force required to extend a molecule by a certain amount (2-10). The data are compiled into a forceextension relationship that gives a characteristic fingerprint for the conformational transitions of the molecule under study. For example, force-extension relationships of polysaccharides such as amylose and dextran (13, 14) display a characteristic plateau (2, 4) that marks forced transitions of the glucose monomers from their chair conformation to the boat-like conformation (4). Similarly, two distinct plateaus in the force-extension curve of pectin (13, 14) report a transition of the galactose rings from the chair conformation to the boat conformation and a subsequent flip of the boat to the inverted chair conformation (5). These observations provide an interesting perspective on the behavior of polysaccharides under mechanical tension (15) and suggest that fingerprints of forced conformational transitions can be used as a means for identifying single polysaccharides molecules in solution (9).In the most typical atomic force microscopy (AFM) experiment, a single molecule adsorbed between a substrate and the cantilever tip is extended vertically at a constant rate while t...

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Chair-boat transitions in single polysaccharide molecules observed with force-ramp AFM

Marszałek

Oberhauser

et al. 2002

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

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136

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“…Thus far, most of the work has been conducted on biopolymers such as polymerase, xantan, proteoglycans, and others. [13][14][15][16] Fascinating examples of the single-chain manipulations are the twisting of DNA molecules by applying an external torque, and the separation of double stranded DNA into two single strands. 17 Similar research for synthetic polymers is just beginning.…”

Section: Introductionmentioning

confidence: 99%

Negative compressibility and nonequivalence of two statistical ensembles in the escape transition of a polymer chain

Skvortsov

Klushin

Leermakers

2007

The Journal of Chemical Physics

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An end-tethered polymer chain compressed between two pistons undergoes an abrupt transition from a confined coil state to an inhomogeneous flowerlike conformation partially escaped from the gap. This phase transition is first order in the thermodynamic limit of infinitely long chains. A rigorous analytical theory is presented for a Gaussian chain in two ensembles: ͑a͒ the H-ensemble, in which the distance H between the pistons plays the role of the independent control parameter, and ͑b͒ the conjugate f-ensemble, in which the external compression force f is the independent parameter. Details about the metastable chain configurations are analyzed by introducing the Landau free energy as a function of the chain stretching order parameter. The binodal and spinodal lines, as well as the barrier heights between the stable and metastable states in the free energy landscape, are presented in both ensembles. In the loop region for the average force with dependence on the distance H ͑i.e., in the H-ensemble͒ a negative compressibility exists, whereas in the f-ensemble the average distance as a function of the force is strictly monotonic. The average fraction of imprisoned segments and the lateral force, taken as functions of the distance H or the average H, respectively, have different behaviors in the two ensembles. These results demonstrate a clear counterexample of a main principle of statistical mechanics, stating that all ensembles are equivalent in the thermodynamic limit. The authors show that the negative compressibility in the escape transition is a purely equilibrium result and analyze in detail the origin of the nonequivalence of the ensembles. It is argued that it should be possible to employ the escape transition and its anomalous behavior in macroscopically homogeneous, but microscopically inhomogeneous, materials.

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Denticity Changes of Hydrotris(pyrazolyl)borate Ligands in RhI and RhIII Compounds: From κ3- to Ionic “κ0”-Tp′

Paneque¹,

Sirol

Trujillo

et al. 2000

Angewandte Chemie

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The formally tridentate cyclopentadienyl and hydrotris-(pyrazolyl)borate ligands are important auxiliary ligands in organometallic chemistry. [1, 2] Most often they act as spectators, and chemical transformation occurs at the metal center or at other coordinated ligands. However, in some instances they may have a noninnocent involvement by means of hapticity changes.Variations in coordination mode are well documented for the cyclopentadienyl system (Cp'). [3,4] Casey and co-workers demonstrated some years ago the interconversion of h 5 -C 5 H 5 , h 1 -C 5 H 5 , and ionic ªh 0 º-C 5 H 5 À compounds in the reaction of [(h 5 -C 5 H 5 )Re(NO)(CH 3 )(PMe 3 )] with PMe 3[5] and proposed an h 3 -C 5 H 5 intermediate for the h 5 > h 1 exchange. In contrast, case of a 6 Â His-tag the more stable one (or ones) is formed more frequently instead. These two coordination bonds differ not only in stability, but also in the ªenergy landscapeº [11] of their transition states, as revealed by the study we carried out on the dependence of their rupture forces on the force loading rate (to be published). This parameter, first introduced by Evans and Ritchie, [12] is equal to the product of the pulling velocity and the ªeffectiveº spring constant (the combination in series of the spring constant of the cantilever and of the molecular bridge).This experiment, although not yet optimized, is casting a new light on our understanding of a bond that forms the basis for more and more important tools for molecular biology. These results make it possible not only to foresee the tremendous possibilities but also the possible problems and pitfalls of this very new and still developing SFM method for studying binding processes. Experimental SectionThe peptide HCys-(Gly) 6 -(His) 2 -OH was kindly provided by Prof. Peggion (Padova), and HCys-(Gly) 6 -(His) 6 -OH was synthesized by Tecnogen (Naples, Italy). Both were synthesized by solid-phase methods, and their purity was controlled by HPLC and MALDI-TOF MS. The Ni ± nta Biacore chip was depleted of nickel(ii) ions by incubation in 0.35 m ethylenediaminetetraacetic acid solution for 2 h; iron(iii) or nickel(ii) ions were reintroduced by treating the chip with a 100 mm solution of FeCl 3 or NiCl 2 and then rinsing with water. Si 3 N 4 AFM cantilevers (DI, Santa Barbara, CA) were metalized by resistive deposition of Ti and then Au 99.99 % (thicknesses of 10 ± 15 nm and 30 ± 40 nm, respectively) at 10 À6 Torr. The tips were then immediately immersed in a 1 mg mL À1 solution of the peptide in phosphate-buffered saline (PBS) at pH 7.4 for 30 min.The spring constants of the cantilevers were determined from their thermal excitation [13] with a precision not higher than 30 %. Four cantilevers were used for the measurements. The values of their spring constants obtained by this method were in the range of 60 to 120 pN nm À1 . Force measurements were carried out in PBS with a Nanoscope III Multimode AFM (DI, Santa Barbara, CA). In this experiment, the unbinding takes place under a rising force and in a ti...

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Single-Molecule Force Spectroscopy on Xanthan by AFM

Cited by 75 publications

References 0 publications

Chair-boat transitions in single polysaccharide molecules observed with force-ramp AFM

Chair-boat transitions in single polysaccharide molecules observed with force-ramp AFM

Negative compressibility and nonequivalence of two statistical ensembles in the escape transition of a polymer chain

Denticity Changes of Hydrotris(pyrazolyl)borate Ligands in RhI and RhIII Compounds: From κ3- to Ionic “κ0”-Tp′

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