Scientific Mission: We aim to understand the mechanisms of assembly and function of biological hydrogels and cellular membranes. To directly assess the supramolecular level of interactions, we tailor make and study well-defined model systems.
The self-organization of molecules into dynamic and hierarchical supramolecular assemblies is a key feature of biological structures. The resulting architectures exhibit new qualities that are distinct from those that characterize its individual components. Our group is particularly interested in two types of assemblies: hydrogel-like structures that are made of flexible biopolymers and cellular membranes.
For a thorough investigation of the physical principles underlying the organization, dynamics and function of these supramolecular architectures, it is desirable to move from living cells to well-controlled models with tunable complexity. We create such model systems on solid supports. Modern techniques of surface biofunctionalization and patterning are employed to guide the assembly down to the nanometer-scale. For the characterization of the model systems, we develop and use a toolbox of biophysical in situ characterization techniques, including quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), reflection interference contrast microscopy (RICM), spectroscopic ellipsometry (SE) and fluorescence methods.
Postdoctoral ResearcherPersonal data
Leire Díaz Ventura
Postdoctoral ResearcherPersonal data
PhD StudentPersonal data
Carolina Araya Callis
Postdoctoral ResearcherPersonal data
Stavros Azinas (CIC bioGUNE)
Aiseta Baradji (University of Liverpool)
PhD StudentPersonal data
María Genua Trullos
Postdoctoral ResearcherPersonal data
This Project is funded by an ERC Starting Grant.Weblink to project
This project aims to understand multivalent interactions between polymers and surfaces. Multivalent binding of polymers to surfaces is an important type of interaction in material, biomedical and life sciences. An example in biological systems is the multivalent binding of hyaluronan (HA) to cell surfaces. The supramolecular organization of HA-rich pericellular matrices has been associated with a number of biological processes such as inflammation and tumor development. It is therefore a subject of intensive studies. Multivalent polymers have also been used for the design of stimuli-responsive films, therapeutic agents, and gene delivery systems. In spite of their importance for material and life sciences, multivalent interactions between polymers and surfaces remain poorly understood.
Using recent achievements of synthetic and surface chemistry, we develop well-defined, highly specific and tunable model systems based on host-guest interactions to quantitatively probe multivalent interactions. Using this experimental platform, we provided the first direct evidence for superselectivity in the multivalent binding of polymers to surfaces (Dubacheva et al. 2014). Superselectivity means that the polymer surface density increases faster than linearly with the density of surface binding sites. Such strong dependence on surface valency allows specific targeting of surfaces displaying binding sites above a threshold surface concentration, while leaving surfaces with lower coverages unaffected. Comparison of our experimental data with theoretical predictions showed that superselectivity is indeed a consequence of multivalency and is enhanced by the ability of polymers to interpenetrate, a unique feature in comparison with other multivalent scaffolds such as particles. The obtained results and future progress in this field should help to understand the regulation of multivalent interactions in biological systems and provide means for the rational design of polymeric drugs tailored for specific bioapplications.
This project is supported by the Marie Curie Career Integration Grant "CellMultiVInt" to Galina V. Dubacheva (grant agreement nº 293803). Details regarding the European Union’s contribution to the project can be found under: http://cordis.europa.eu/project/rcn/100141_en.html.
All macromolecular transport between the cytosol and the nucleosol of living cells occurs through nuclear pore complexes (NPCs). The transport is selective: objects beyond a certain size (30kDa) need to attach to soluble nuclear transport receptors (NTRs) in order to be channeled efficiently through the pore. A supramolecular assembly of specialized and natively unfolded protein domains (FG repeat domains) within the NPC is thought to be the key component of the NPC´s permeability barrier. How this self-organized polymer meshwork generates transport selectivity is at present only poorly understood.
We aim to understand the relation between the organizational and dynamic features of FG-nucleoporin assemblies, their physico-chemical properties, and the resulting biological functions. Using an approach that combines tailor-made biomimetic in vitro model systems, surface-sensitive in situ analysis techniques, and polymer physics theory, we quantitatively study these relationships on the supramolecular level, a level that for this type of assemblies is hardly accessible with conventional biological and biophysical approaches. The model systems are well-defined allowing tight control over composition and supramolecular structure (Eisele et al. 2010; Eisele et al. 2012; Eisele et al. 2013). This work is highly interdisciplinary and, if successful, will increase our mechanistic understanding of nuclear transport and provide guidelines for the rational design of novel artificial separation devices for biotechnological applications.
This project was supported by the Marie Curie IEF grant "Nuclear Pore" to Raphael Zahn (grant agreement nº 327975). Details regarding the European Union’s contribution to the project can be found under: http://cordis.europa.eu/project/rcn/107088_en.html.
Many cells equip themselves with a hydrogel-like coat that is rich in the polysaccharide hyaluronan. This pericellular coat can reach a thickness of several micrometers. It is invisible in common light microscopy, since its extreme hydration renders the optical contrast very low. The grafting of hyaluronan to the cell membrane and its interaction with hyaluronan-binding molecules can give rise to different supramolecular structures, such as cross-linked networks or polyelectrolyte brushes or self-assembled monolayers (Atilli et al. 2012).
By reconstituting these intriguing structures in vitro, the physico-chemical properties of pericellular coats can be quantified (Baranova et al. 2011). We create model systems of the pericellular coat that are based on supported lipid bilayers (Richter et al. 2006). These immobilization platforms allow us to create hyaluronan layers with well-defined composition and structure, such as brushes of end-grafted hyaluronan (Richter et al. 2007).
Under inflammatory conditions and ovulation, hyaluronan-rich coats undergo significant remodeling. The inflammation-associated protein TSG-6 was hypothesized to be implicated in the coat remodeling by cross-linking HA chains. With the aid of our model systems, we could provide evidence that TSG-6 can indeed act as an effective HA cross-linker, and shed insight into the cross-linking mechanism. The cross-linking units are TSG-6 oligomers which form upon binding of TSG-6 to HA (Baranova et al. 2011). TSG-6 collapses and rigidifies hyaluronan films. Cross-linking might hence influence the mechanical environment of cells and the local organization of the pericellular coat (glycocalyx) might also serve as a signal for leukocyte recruitment to sites of inflammation.
CD44 is a major cell surface receptor for hyaluronan (HA). It is found on many cell types, and of particular importance in inflammation-like processes and tumor metastasis. The interaction of hyaluronan with the cell membrane is thought to be stabilized by multivalent interactions between polymeric HA and several cell surface receptors. The molecular (and supra molecular) mechanisms behind the regulation of binding, and in particular the different biological functions that are elicited by HA of different molecular weight, are currently not well understood.
We have designed tunable in-vitro model systems that mimic the cell surface in the sense that the HA binding domain of CD44 is immobilized in its native orientation and at controlled density to a supported lipid bilayer (SLB). Employing techniques such as QCM-D, SE and RICM and concepts from polymer theory, we analyze qualitatively and quantitatively, how the multivalent presentation of CD44 on the membrane surface regulates the binding and self-organization of hyaluronan and its complexes (Wolny et al. 2010).
Quartz crystal microbalance with dissipation monitoring (QCM-D) has become a popular tool to investigate biomolecular interaction phenomena at surfaces (Reviakine et al. 2011). In contrast to optical mass-sensitive techniques, which commonly detect the adsorbed nonhydrated mass, the mechanically coupled mass measured by QCM-D includes a significant amount of water. A mechanistic and quantitative picture of how the surrounding liquid couples to the deposited molecules has long been elusive for apparently simple phenomena like the random adsorption of proteins or other nanometre-sized particles on a planar surface.
We employ in situ combinations of QCM-D with other sensing techniques (in particular ellipsometry) and theoretical modelling to elucidate this question (Bingen et al. 2008). The insights are used for the development of novel sensing applications. With this methodology, it is for example possible to detect the clustering of proteins on supported lipid bilayers without any labels.
We have developed an efficient and robust method to dynamically modulate the glycolipid content in supported lipid bilayers (Carton et al. 2010). The method is based on glycolipid transfer protein, a soluble protein that can selectively transfer glycolipids from one membrane compartment to another. It provides quantitative control on the lipid composition of the bulk facing bilayer leaflet. Owing to the importance of glycolipids in the function of cell membranes and membrane proteins, the method may find widespread use in membrane research.
|10/07/14||Elisa Migliorini won the "International Society of Matrix Biology Young Scientist Award" at the Gordon Research Seminar "Proteoglycans" in Andover (USA).|
|03/02/14||Maria Genua joins the group as a Postdoc. Welcome!.|
|09/01/14||Our paper on superselective targeting using multivalent polymers was accepted for publication in the Journal of the American Chemical Society|
|07/10/13||Stavros Azinas joins the group as a Technician. Bienvenido!|
|25/08-14/ 09/2013||Ralf will give three lectures at theEuropean School on Nanosciences and Nanotechnologies (ESONN; 25/08-14/09/2013, Grenoble).|
|15-19/09/2013||Galina Dubacheva will give a talk at theInternational Soft Matter Conference (15-19/09/2013, Rome) entitled "Highly tunable host-guest model systems to study multivalent self-assembly of polymers at functional interfaces".|
|05/09/2013||Our manuscript on the ternary interactions between IaI, TSG-6 and hyaluronan chains was accepted in The Journal of Biological Chemistry. Congratulations to Natalia in particular!|
|04/09/2013||Our paper on the implications of cohesive FG domain interactions for selective transport through the nuclear pore was accepted in Biophysical Journal. Congratulations to Nico in particular!|
|30/06-05/07/2013||Workshop"Biological Surfaces and Interfaces" in Saint Feliu de Guixols, Catalonia, Spain.|
|28/06/2013||Natalia defends her PhD thesis. Congratulations!|
|13/06/2013||Raphael wins theMaterials Research Prize 2013. The prize awards the best PhD thesis with industrial relevance carried out at ETH Zurich in the area of Materials. Congratulations!|
|02/05/2013||Nico defends his PhD thesis. Congratulations!|
|01/05/2013||Fouzia Bano joins the group as a Postdoc. Welcome!|
|08/04/2013||Severin Ehret joins the group as a PhD student. Bienvenido!|
|08/04/2013||Carolina Araya joins the group as a Technician. Bienvenida!|
|03/04/2013||Totta Kasemo joins the group as a BSc student. Bienvenida!|
|01/12/2012||Raphael Zahn joins the group as a Postdoc. Welcome!|
|01/11/2012||Welcome to the world Timur, and congratulations Natalia!|
|17/09/2012||Xinyue Chen joins the group as a PhD student. Huan ying and bienvenida!|
|27/07/2012||Ram defends his PhD thesis. Congratulations, and all the best at King's College in London!|
|14/07/2012||Nico receives the 1st Poster Price at the Workshop "Physical Chemistry at Biointerfaces II." Well done!|
|09-14/07/2012||Workshop "Physical Chemistry at Biointerfaces II" at CIC biomaGUNE. A lovely week of stimulation and interaction!|
|28/03/2012||Our manuscript on the compressive mechanics of hyaluronan brushes is accepted in Biomacromolecules. Congratulations, to Ram in particular!|
|19/03/2012||Galina Dubacheva joins the group as a Postdoc with funding from a Marie Curie Career Integration Grant. Welcome!|
|04/01/2012||Our paper on the combination of colloidal probe AFM and RICM for force measurements on thin hydrated films was accepted in Langmuir. Congratulations, to Ram in particular!|
|Raphael Zahn|| Postdoc |
December 2012 - October 2014
"Studying the physico-chemical properties of nucleo-cytoplasmic transport."
|Severin Ehret|| Graduate project student |
April 2013 - May 2014
"Contributions in the study of the mechanisms of selective nucleo-cytoplasmic transport."
|Totta Kasemo|| Bachelor Student |
April 2013 - August 2013
"Studying structural changes in a model system of the nuclear pore permeability barrier and applying polymer theory."
|Nico Eisele|| Postdoc |
May 2013 - July 2013
2009 - May 2013
"Nanoscale model systems of the permeability barrier of nuclear pore complexes."
|Seetharamaiah Attili|| PhD Student |
May 2008 - August 2012
"Compressive mechanics of hyaluronan-rich pericellular matrices - A study on a biomimetic model film, combining atomic force and reflection interference contrast microscopy."
|Anja Bernecker|| PostDoc |
July 2010 - December 2011
"Physical principles of hyaluronan-cell surface interactions."
|Georgina Ormaza|| Technician |
July - December 2011
|Patricia Wolny|| PhD Student |
January 2006 - December 2010
"Novel model systems for the investigation of multivalent protein-hyaluronan interactions on the cell surface."
|Barthélémy Delorme|| MSc I Project (from University Bordeaux I, France |
April - August 2010
"Fluorescence recovery after photobleaching - from 2D to 3D."
|Ixaskun Carton|| Technician |
January 2008 - May 2010
"Dynamic modulation of the composition of supported lipid membranes by glycolipid transfer protein."
|Olga Martínez Ávila|| Postdoctoral Summer Visit |
June - July 2009
"Glyco-functionalization of nanostructured surfaces."
|Nicolás Heim|| MSc I Project (from University Bordeaux I, France) |
April - May 2009
"Solvation effects in the QCM-D."
|Stefan Stahl|| Summer Research Student (from LMU Munich, Germany) |
July - September 2008
"In Situ combination of QCM-D and ellipsometry."