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Yael Politi Group

Chitin based biological materials and biomineralization

Portrait Yael Politi

The arthropod cuticle is a powerful model system for studying how biocomposite materials properties are governed by their molecular interactions and underlying nano-scale structure, and how these properties are tuned to produce versatile multifunctional materials. The research in the group aims at a quantitative definition of the structure-properties relationships in the cuticle. Specifically, we investigate the molecular interactions between cuticle components and how these interaction determine the materials properties over several length scales to enable a particular function, for example venom injection by the spider fang, or a combination of multiple functions such as in the main vibration mechano-sensor of the wandering spider Cupiennius salei, which also functions as a proprioceptor. Further, we are working towards understanding cuticle formation mechanisms, in particular how fiber orientation is controlled by the organism. Here, we aim to determine what is the extent of cellular control over fiber orientation as opposed to the role of chitin-protein co-assembly in determining the final fiber architecture. Despite years of research this is still an unresolved fundamental question in the understanding of the formation of biological fibrous matrices. We address this question using EM and light microscopy of biological cuticle deposition as well as in vitro assays of chitin-protein co-assembly.

We are also intrigued by biomineralization in marine organisms, and in particular Echinoderms. We study sea urchin skeletal element morphogenesis and crystallography in order to understand the manner in which cells interact with minerals and control their shape. The sea urchin skeletal elements are often made of single crystals of calcite and exhibit complex shapes and curved, smooth surfaces, an unusual morphology for crystalline material. This is most likely owed to their formation involving an amorphous precursor in confined spaces defined by the skeletogenic cells. We therefore also study the amorphous to crystalline transition in sea urchin skeletal elements as well as in in-vitro systems, and in particular the effect of water, organic and inorganic additives on the transformation energy landscape and kinetics.

Yael Politi Research: Figure
Microvilli structure and fiber deposition within the assembly zone. FIB/SEM images (A, D) obtained by re-slicing the 3D datasets shown in Figure 2 along (t) (top) and (z) (bottom) directions, for Night (A) and Day (D) samples. The comparison shows that the microvilli have similar dimensions in (z) and (t) directions in the Night samples (A, top and bottom) whereas they are elongated along the (z) direction in the Day samples (D, top). (B-F) Volume rendering of the FIB/SEM data in (A) and (D) The plaques are depicted in bright blue. chitin fiber bundles in yellow. (B, E) (zr), and (tr) plane views of resliced volumes. Only one plaque (bright blue arrowhead) is situated at the tips of each microvillus during the deposition of twisted plywood structure (B), but 2 or 3 plaques are observed on top of microvilli merged along the (z) direction during the deposition of parallel fibers (E). (C, F) 3D volume rendering of the chitin fibers/fiber bundles (yellow) observed in the assembly zone and the apical cell surface in twisted plywood formation (C) and parallel fiber formation (F) samples. White dotted lines in (F) indicate merged microvilli structures. (G-H) WAXS data of adult locust tibia grown in conditions favoring parallel fiber alignment. (G) 2D XRD pattern and (H) azimuthally integrated 1D XRD profiles in the equatorial direction (red line, red cake on 2D pattern) and meridian (black line, black cake on 2D pattern), obtained from the endocuticle of a locust reared

Future Projects and Goals

The ultimate goal of the group is to twofold; we aim at understating the structure-properties-function relationships in biological materials, mainly that of the arthropod cuticle, and to elucidate the mechanisms of their formation. We therefore employ biological as well as material-science perspectives and methodologies to solve these questions. Currently we study how cuticular structures function as mechano-sensors in spiders and in insects, how the optical properties of the horse show crab cornea are determined by its underlying fiber architecture, and how cuticular tools achieve impressing mechanical properties in the absences of mineralization. In addition, we study the molecular interactions within the cuticle, namely, chitin-protein, inter-protein and chitin-protein-water interactions.

Methodological and Technical Expertise

  • Small and wide-angle x-ray scattering (SAXS, WAXS)
  • (cryo)FIB/SEM 3D imaging and 3D automatic segmentation and data analysis
  • X-ray microtomography
  • X-ray and vibrational spectroscopy (XAS, XRF, EDX, Raman, FTIR)
  • Wide-field, phase-contrast, polarized light and fluoresce (CLSM) microscopy

Currently Recruiting

Yael Politi is recruiting in the PhD Fall Selection 2020 (call is closed)

CV

2019
Professor for Bioprospecting, B CUBE Center and Department of Chemistry, Dresden University of Technology (Germany)

2012–2019
Group leader, Max-Planck Institute of Colloids and Interfaces, Department of Biomaterials, Research Campus Golm, Potsdam, Germany

2009–2012
Post-Doctoral Fellowship, Max-Planck Institute of Colloids and Interfaces, Department of Biomaterials, Research Campus Golm, Potsdam, Germany

2005–2009
Ph.D. in Structural Biology, Faculty of Chemistry, Weizmann Institute of Science, Rehovot, Israel

More Information

Yael Politi at B CUBE

Selected Publications

Tadayon M, Younes-Metzler O, Shelef Y, Zaslansky P, Rechels A, Berner A, Zolotoyabko E, Barth FG, Fratzl P, Bar-On B, Politi Y
Adaptations for wear resistance and damage resilience: micromechanics of spider cuticular “tools”.
Adv. Funct. Mater., in print (2020)

Sviben S, Spaeker O, Bennet M, Albéric M, Dirks JH, Moussian B, Fratzl P, Bertinetti L, Politi Y
Epidermal cell surface structure and chitin-protein co-assembly determine fiber architecture in the Locust cuticle.
ACS Appl. Mater. Interfaces, in print (2019)

Albéric M, Bertinetti L, Zou Z, Fratzl P, Habraken W, Politi Y
The Crystallization of Amorphous Calcium Carbonate is Kinetically Governed by Ion Impurities and Water.
Adv. Sci. 5, 1701000 (2018)

Valverde Serrano C, Leemreize H, Bar-On B, Barth FG, Fratzl P, Zolotoyabko E, Politi Y
Ordering of protein and water molecules at their interfaces with chitin nano-crystals.
J Struct Biol 193(2):124–31 (2015)

Erko M, Younes-Metzler O, Rack A, Zaslansky P, Young S, Milliron G, Chyasnavichyus M, Barth FG, Fratzl P, Tsukruk V, Zlotnikov I, Politi Y.
Micro- and nano-structural details of a spider’s filter for substrate vibrations: Relevance for low frequency signal transmission.
J R Soc Interface 12(104):20141111 (2015)

Contact

B CUBE – Center for Molecular Bioengineering
TU Dresden
Tatzberg 41
01307 Dresden
Germany