Publications by Guillaume Witz

Assessing dystrophies and other muscle diseases at the nanometer scale by atomic force microscopy

Harald Brune, Andrzej Kulik, Nicolas Mermod, Giovanni Dietler, Guillaume Witz, Stefania Puttini

Aim: Atomic force microscopy nanoindentation of myofibers was used to assess and quantitatively diagnose muscular dystrophies from human patients. Materials & methods: Myofibers were probed from fresh or frozen muscle biopsies from human dystrophic patient ...

Future Medicine2014

DNA knots and DNA supercoiling

Giovanni Dietler, Andrzej Stasiak, Guillaume Witz

2011

Cooperative kinking at distant sites in mechanically stressed DNA

Andrzej Stasiak, Guillaume Witz, Julien Dorier, Davide Demurtas

In cells, DNA is routinely subjected to significant levels of bending and twisting. In some cases, such as under physiological levels of supercoiling, DNA can be so highly strained, that it transitions into non-canonical structural conformations that are c ...

Oxford University Press2011

Tightening of DNA knots by supercoiling facilitates their unknotting by type II DNA topoisomerases

Giovanni Dietler, Andrzej Stasiak, Guillaume Witz

Using numerical simulations, we compare properties of knotted DNA molecules that are either torsionally relaxed or supercoiled. We observe that DNA supercoiling tightens knotted portions of DNA molecules and accentuates the difference in curvature between ...

2011

Conformation of Ring Polymers in 2D Constrained Environments

Giovanni Dietler, Guillaume Witz, Kristian Rechendorff

The combination of ring closure and spatial constraints has a fundamental effect on the statistics of semiflexible polymers such as DNA. However, studies of the interplay between circularity and constraints are scarce and single-molecule experimental data ...

American Physical Society2011

DNA Topology : A Biophysical Study of DNA Rings, Knots, and Catenanes by Means of Atomic Force Microscopy and Numerical Simulations

Guillaume Witz

This thesis explores different aspects of DNA topology through experimental and numerical techniques. Topology is a vast mathematical field, that deals with the spatial properties of objects undergoing continuous deformations, but here it is restricted to ...

EPFL2010

Excluded Volume Effects on Semiflexible Ring Polymers

Giovanni Dietler, Guillaume Witz

Two-dimensional semiflexible polymer rings are studied both by imaging circular DNA adsorbed on a mica surface and by Monte Carlo simulations of phantom polymers as well as of polymers with finite thickness. Comparison of size and shape of the different mo ...

American Chemical Society (ACS)2010

Interplay of DNA supercoiling and catenation during the segregation of sister duplexes

Andrzej Stasiak, Guillaume Witz, Pablo Hernandez

The discrete regulation of supercoiling, catenation and knotting by DNA topoisomerases is well documented both in vivo and in vitro, but the interplay between them is still poorly understood. Here we studied DNA catenanes of bacterial plasmids arising as a ...

Oxford University Press2009

Persistence length and scaling properties of single-stranded DNA adsorbed on modiﬁed graphite

Giovanni Dietler, Guillaume Witz, Kristian Rechendorff

We have characterized the polymer physics of single-stranded DNA (ssDNA) using atomic force microscopy. The persistence length l(p) of circular ssDNA adsorbed on a modified graphite surface was determined independently of secondary structure. At a very low ...

2009

The promotion of secondary structures in single-stranded DNA by drugs that bind to duplex DNA: an atomic force microscopy study

Giovanni Dietler, Guillaume Witz, Kristian Rechendorff

We study the behavior of single-stranded DNA (ssDNA) in the presence of well-known drugs with either an intercalating binding mode, such as daunorubicin, actinomycin D, and chloroquine, or a minor groove binding mode, such as netropsin and berenil, by atom ...

2008

Conformation of Circular DNA in Two Dimensions

Giovanni Dietler, Guillaume Witz, Kristian Rechendorff

The conformation of circular DNA molecules of various lengths adsorbed in a 2D conformation on a mica surface is studied. The results confirm the conjecture that the critical exponent ν is topologically invariant and equal to the self-avoiding walk value ( ...

American Physical Society2008

Fractal dimension and localization of DNA knots

Giovanni Dietler, Paolo De Los Rios, Guillaume Witz, Erika Ercolini

The scaling properties of DNA knots of different complexities were studied by atomic force microscope. Following two different protocols DNA knots are adsorbed onto a mica surface in regimes of (i) strong binding, that induces a kinetic trapping of the thr ...

American Physical Society2007

Observation of single-stranded DNA on mica and highly oriented pyrolytic graphite by atomic force microscopy

Giovanni Dietler, Guillaume Witz, Serguei Sekatski, Dmitry Klinov

2006