Publications by Sonia Antoranz Contera

Multifrequency AFM reveals lipid membrane mechanical properties and the effect of cholesterol in modulating viscoelasticity.

Proceedings of the National Academy of Sciences of the United States of America 115 (2018) 2658-2663

Z Al-Rekabi, S Contera

The physical properties of lipid bilayers comprising the cell membrane occupy the current spotlight of membrane biology. Their traditional representation as a passive 2D fluid has gradually been abandoned in favor of a more complex picture: an anisotropic time-dependent viscoelastic biphasic material, capable of transmitting or attenuating mechanical forces that regulate biological processes. In establishing new models, quantitative experiments are necessary when attempting to develop suitable techniques for dynamic measurements. Here, we map both the elastic and viscous properties of the model system 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers using multifrequency atomic force microscopy (AFM), namely amplitude modulation-frequency modulation (AM-FM) AFM imaging in an aqueous environment. Furthermore, we investigate the effect of cholesterol (Chol) on the DPPC bilayer in concentrations from 0 to 60%. The AM-AFM quantitative maps demonstrate that at low Chol concentrations, the lipid bilayer displays a distinct phase separation and is elastic, whereas at higher Chol concentration, the bilayer appears homogenous and exhibits both elastic and viscous properties. At low-Chol contents, the Estorage modulus (elastic) dominates. As the Chol insertions increases, higher energy is dissipated; and although the bilayer stiffens (increase in Estorage), the viscous component dominates (Eloss). Our results provide evidence that the lipid bilayer exhibits both elastic and viscous properties that are modulated by the presence of Chol, which may affect the propagation (elastic) or attenuation (viscous) of mechanical signals across the cell membrane.

How to probe the spin contribution to momentum relaxation in topological insulators.

Nature communications 9 (2018) 56-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

Topological insulators exhibit a metallic surface state in which the directions of the carriers' momentum and spin are locked together. This characteristic property, which lies at the heart of proposed applications of topological insulators, protects carriers in the surface state from back-scattering unless the scattering centres are time-reversal symmetry breaking (i.e. magnetic). Here, we introduce a method of probing the effect of magnetic scattering by decorating the surface of topological insulators with molecules, whose magnetic degrees of freedom can be engineered independently of their electrostatic structure. We show that this approach allows us to separate the effects of magnetic and non-magnetic scattering in the perturbative limit. We thereby confirm that the low-temperature conductivity of SmB6 is dominated by a surface state and that the momentum of quasiparticles in this state is particularly sensitive to magnetic scatterers, as expected in a topological insulator.

Amphiphilic DNA tiles for controlled insertion and 2D assembly on fluid lipid membranes: the effect on mechanical properties

Nanoscale 9 (2017) 3051-3058

C Dohno, S Makishi, K Nakatani, S Contera

Magneto-electrical orientation of lipid-coated graphitic micro-particles in solution

RSC Adv. 6 (2016) 46643-46653

J Nguyen, S Contera, I Llorente García

Developing a Single-Molecule Fluorescence Tool to Quantify DNA Damage

BIOPHYSICAL JOURNAL 110 (2016) 164A-164A

HL Miller, AJM Wollman, KE Dunn, AM Hirst, SA Contera, S Johnson, D O'Connell, P O'Toole, AM Tyrrell, MC Leake

Designer cantilevers for even more accurate quantitative measurements of biological systems with multifrequency AFM

Nanotechnology 27 (2016) 132501-132501

S Contera

Effect of intra-membrane C 60 fullerenes on the modulus of elasticity and the mechanical resistance of gel and fluid lipid bilayers

Nanoscale 7 (2015) 17102-17108

J Zhou, D Liang, S Contera

2015 4 th TERMIS World CongressBoston, MassachusettsSeptember 8–11, 2015

Tissue Engineering Part A 21 (2015) S-1-S-413

Sub-nanoscale free volume and local elastic modulus of chitosan–carbon nanotube biomimetic nanocomposite scaffold-materials

J. Mater. Chem. B 3 (2015) 3169-3176

E Axpe, L Bugnicourt, D Merida, M Goiriena-Goikoetxea, I Unzueta, R Sanchez-Eugenia, JA Garcia, F Plazaola, S Contera

Three strategies to stabilise nearly monodispersed silver nanoparticles in aqueous solution.

Nanoscale Res Lett 7 (2012) 151-

AP Stevenson, D Blanco Bea, S Civit, S Antoranz Contera, A Iglesias Cerveto, S Trigueros

Silver nanoparticles are extensively used due to their chemical and physical properties and promising applications in areas such as medicine and electronics. Controlled synthesis of silver nanoparticles remains a major challenge due to the difficulty in producing long-term stable particles of the same size and shape in aqueous solution. To address this problem, we examine three strategies to stabilise aqueous solutions of 15 nm citrate-reduced silver nanoparticles using organic polymeric capping, bimetallic core-shell and bimetallic alloying. Our results show that these strategies drastically improve nanoparticle stability by distinct mechanisms. Additionally, we report a new role of polymer functionalisation in preventing further uncontrolled nanoparticle growth. For bimetallic nanoparticles, we attribute the presence of a higher valence metal on the surface of the nanoparticle as one of the key factors for improving their long-term stability. Stable silver-based nanoparticles, free of organic solvents, will have great potential for accelerating further environmental and nanotoxicity studies.PACS: 81.07.-b; 81.16.Be; 82.70.Dd.

Temperature-dependent phase transitions in zeptoliter volumes of a complex biological membrane

Nanotechnology 22 (2011)

MP Nikiforov, S Hohlbauch, WP King, K Vöitchovsky, SA Contera, S Jesse, SV Kalinin, R Proksch

Phase transitions in purple membrane have been a topic of debate for the past two decades. In this work we present studies of a reversible transition of purple membrane in the 50-60 °C range in zeptoliter volumes under different heating regimes (global heating and local heating). The temperature of the reversible phase transition is 52 ± 5 °C for both local and global heating, supporting the hypothesis that this transition is mainly due to a structural rearrangement of bR molecules and trimers. To achieve high resolution measurements of temperature-dependent phase transitions, a new scanning probe microscopy-based method was developed. We believe that our new technique can be extended to other biological systems and can contribute to the understanding of inhomogeneous phase transitions in complex systems. © 2011 IOP Publishing Ltd Printed in the UK & the USA.

Bilayer-mediated clustering and functional interaction of MscL channels

Biophysical Journal 100 (2011) 1252-1260

SL Grage, AM Keleshian, T Turdzeladze, AR Battle, WC Tay, RP May, SA Holt, SA Contera, M Haertlein, M Moulin, P Pal, PR Rohde, TV Forsyth, A Watts, KC Huang, AS Ulrich, B Martinac

Mechanosensitive channels allow bacteria to respond to osmotic stress by opening a nanometer-sized pore in the cellular membrane. Although the underlying mechanism has been thoroughly studied on the basis of individual channels, the behavior of channel ensembles has yet to be elucidated. This work reveals that mechanosensitive channels of large conductance (MscL) exhibit a tendency to spatially cluster, and demonstrates the functional relevance of clustering. We evaluated the spatial distribution of channels in a lipid bilayer using patch-clamp electrophysiology, fluorescence and atomic force microscopy, and neutron scattering and reflection techniques, coupled with mathematical modeling of the mechanics of a membrane crowded with proteins. The results indicate that MscL forms clusters under a wide range of conditions. MscL is closely packed within each cluster but is still active and mechanosensitive. However, the channel activity is modulated by the presence of neighboring proteins, indicating membrane-mediated protein-protein interactions. Collectively, these results suggest that MscL selfassembly into channel clusters plays an osmoregulatory functional role in the membrane. © 2011 by the Biophysical Society.

Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy.

Nat Nanotechnol 6 (2011) 809-814

A Raman, S Trigueros, A Cartagena, APZ Stevenson, M Susilo, E Nauman, SA Contera

The nanomechanical properties of living cells, such as their surface elastic response and adhesion, have important roles in cellular processes such as morphogenesis, mechano-transduction, focal adhesion, motility, metastasis and drug delivery. Techniques based on quasi-static atomic force microscopy techniques can map these properties, but they lack the spatial and temporal resolution that is needed to observe many of the relevant details. Here, we present a dynamic atomic force microscopy method to map quantitatively the nanomechanical properties of live cells with a throughput (measured in pixels/minute) that is ∼10-1,000 times higher than that achieved with quasi-static atomic force microscopy techniques. The local properties of a cell are derived from the 0th, 1st and 2nd harmonic components of the Fourier spectrum of the AFM cantilevers interacting with the cell surface. Local stiffness, stiffness gradient and the viscoelastic dissipation of live Escherichia coli bacteria, rat fibroblasts and human red blood cells were all mapped in buffer solutions. Our method is compatible with commercial atomic force microscopes and could be used to analyse mechanical changes in tumours, cells and biofilm formation with sub-10 nm detail.

Controlled ionic condensation at the surface of a native extremophile membrane.

Nanoscale 2 (2010) 222-229

S Antoranz Contera, K Voïtchovsky, JF Ryan

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.

Direct mapping of the solid-liquid adhesion energy with subnanometre resolution

Nature Nanotechnology 5 (2010) 401-405

K Voïtchovsky, JJ Kuna, SA Contera, E Tosatti, F Stellacci

Solid-liquid interfaces play a fundamental role in surface electrochemistry, catalysis, wetting, self-assembly and biomolecular functions. The interfacial energy determines many of the properties of such interfaces, including the arrangement of the liquid molecules at the surface of the solid. Diffraction techniques are often used to investigate the structure of solid-liquid interfaces, but measurements of irregular or inhomogeneous interfaces remain challenging. Here, we report atomic-and molecular-resolution images of various organic and inorganic samples in liquids, obtained with a commercial atomic force microscope operated dynamically with small-amplitude modulation. This approach uses the structured liquid layers close to the solid to enhance lateral resolution. We propose a model to explain the mechanism dominating the image formation, and show that the energy dissipated during this process is related to the interfacial energy through a readily achievable calibration curve. Our topographic images and interfacial energy maps could provide insights into important interfaces. © 2010 Macmillan Publishers Limited. All rights reserved.

Clustering and Functional Interaction of MscL Channels


AM Keleshian, SL Grage, T Turdzeladze, AR Battle, WC Tay, SA Holt, SA Contera, M Haertlein, M Moulin, P Pal, PR Rohde, KC Huang, A Watts, AS Ulrich, B Martinac

Lateral coupling and cooperative dynamics in the function of the native membrane protein bacteriorhodopsin

Soft Matter 5 (2009) 4899-4904

K Voïtchovsky, SA Contera, JF Ryan

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 (2009) 153-158

H Yamashita, K Voïtchovsky, T Uchihashi, SA Contera, JF Ryan, T Ando

We have used high-speed atomic force microscopy to study the dynamics of bacteriorhodopsin (bR) molecules at the free interface of the crystalline phase that occurs naturally in purple membrane. Our results reveal temporal fluctuations at the crystal edges arising from the association and dissociation of bR molecules, most predominantly pre-formed trimers. Analysis of the dissociation kinetics yields an estimate of the inter-trimer single-bond energy of -0.9kcal/mol. Rotational motion of individual bound trimers indicates that the inter-trimer bond involves W10-W12 tryptophan residues.

Effect of acid treatment on the structure and electrical properties of nitrogen-doped multiwalled carbon nanotubes

Journal of Physical Chemistry C 112 (2008) 1908-1912

HJ Burch, E Brown, SA Contera, NC Toledo, DC Cox, N Grobert, L Hao, JF Ryan, JA Davies

Nitrogen-doped multiwalled carbon nanotubes (CN x MWNTs) have been cut to an average length of ∼1 μm by room-temperature acid treatment. Imaging of the surface morphology of the CN x , MWNTs (x = 2-5%) after sonication in acid or in ethanol (as a control) allowed the relationship between surface structure and acid cutting to be characterized. The effect of the acid treatment on the electrical conductance of the CN x MWNTs was also determined. The conductance of acid-treated CN x MWNTs was found to vary significantly within the sample and to be lower than the value of 1.0 G 0 observed for as-produced CS x MWNTs. The G - V curves reported for acid-treated CN x MWNTs had an average slope of 0.19 G 0 /V, which is significantly smaller than the average of 0.70 G 0 /V measured for as-produced CN x MWNTs. Acid-treated CN x MWNTs exhibited a more rapid electrical breakdown with larger current steps, indicating the breakdown of several MWNT layers simultaneously. © 2008 American Chemical Society.

Doping of carbon nanotubes with nitrogen improves protein coverage whilst retaining correct conformation.

Nanotechnology 19 (2008) 384001-

HJ Burch, SA Contera, MRR de Planque, N Grobert, JF Ryan

Relevant parameters for non-covalent protein functionalization of carbon nanotubes are explored. Multiwalled carbon nanotubes are carboxylated and functionalized with metalloproteins. Using atomic force microscopy (AFM) we quantitatively determine that coverage with nitrogen-doped multiwalled carbon nanotubes is superior compared to coverage with un-doped multiwalled carbon nanotubes, due to enhanced carboxylation. Conformational analysis using a combination of AFM, antibody binding assays, circular dichroism and UV-visible spectroscopy demonstrates that the metalloproteins retain their native structure when adsorbed to nitrogen-doped multiwalled carbon nanotubes irrespective of their size, charge or folding motif.