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Research Units

Biosurfaces

Laboratory 2

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.

Person in charge

Ralf Richter
  • Email: rrichter@cicbiomagune.es
  • Telephone no.: +34 943 00 53 29
  • Address: Parque tecnológico de San Sebastián
    Ed. Pº Miramón 182, Guipúzcoa
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Members

Natalia Baranova

Postdoctoral Researcher

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Leire Díaz Ventura

Technician

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Galina Dubacheva

Postdoctoral Researcher

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Xinyue Chen

PhD Student

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Raphael Zahn

Postdoctoral Researcher

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Carolina Araya Callis

Technician

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Severin Ehret

PhD Student

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Fouzia Bano

Postdoctoral Researcher

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Stavros Azinas (CIC bioGUNE)

Technician

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Aiseta Baradji

PhD Student

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María Genua Trullos

Postdoctoral Researcher

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Projects

Biomolecular Hydrogels - From Supramolecular Organization and Dynamics to Biological Function

This Project is funded by an ERC Starting Grant.

Weblink to project
Superselective targeting using multivalent polymers

This project is supported by the Marie Curie Career Integration Grant "CellMultiVInt" to G. V. Dubacheva.


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.



Model Systems of the Pericellular Coat

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.



Interaction of Hyaluronan with the Cell Surface

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).



The Permeability Barrier of Nuclear Pore Complexes

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 design tailor-made nanoscale model systems of the permeability barrier of NPCs, such as thin films of FG-repeat domains that are end-grafted to planar solid supports (Eisele et al. 2010). The physico-chemical properties of the films and their selective interaction with NTRs and other probes are characterized in detail by a combination of biophysical surface-sensitive techniques (Eisele et al. 2012). We employ the nanoscale model systems together with concepts from polymer physics to gain insight into the inter-relationship between supramolecular structure and function of the permeability barrier.



Nanoparticles & Acousto-Mechanical Sensing

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.



Dynamic Tuning of Model Membrane Lipid Composition

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.



Publications

publications list

Additional information

News

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!


Alumni

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
PhD Student
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."