6533b7dafe1ef96bd126e79c

RESEARCH PRODUCT

Inorganic/Organic interface in biominerals : unveiling the complex structure of two calcitic biomineral models, the red coral Corallium rubrum and the mediterranean fan mussel Pinna nobilis

subject

description

Biominerals are organo-minerals structures produced by living systems. Since the Cambrian, they contribute to the adaptation of living organisms to different environments by fulfilling a variety of combined functions that go along with adapted morphologies. One of the aims of biomineralization is to understand how organisms "sculpt" these complex morphologies, in particular at nano and molecular scales. The aim of this PhD work was to understand the complex relationships between the organic and mineral phases. To this end, I focused my analyses on two calcitic biomineral models: 1) the red coral Corallium rubrum and 2) the prismatic shell of the Mediterranean fan mussel Pinna nobilis. My work deals with two different – but complementary- approaches to understand the complex mechanism of biomineralization: one is based on physio-chemical characterization, the other, on biochemical and proteomic analysis of the organics contained in the biomineral.For physio-chemical characterization (Chapter 2 of my thesis), I have used three different imaging techniques available at Synchrotron-SOLEIL: X-ray microtomography, Deep-UV luminescence imaging and at last, Secondary harmonic generation (SHG) microscopy. All three were used for analyzing the red coral model. X-ray microtomography evidenced the evolution of the microporosity at the very first steps of calcification of the coral branch tips. Deep-UV luminescence imaging was used to determine the distribution of organics, particularly proteins and pigment, and pointed out the presence of heterogeneously distributed micro-protuberances that likely play important functions in epithelium adhesion to the skeleton. Finally, SHG microscopy revealed peculiar radial patterns in the red coral skeleton, that are likely due to aligned organic molecules, like collagen or pigments. These combined high-resolution techniques illustrate the structural complexity of the red coral. We believe that they will develop in the future, for studying complex natural objects, like biominerals.The nature of the organic matrix contained in the calcitic prismatic shell layer of the fan mussel Pinna nobilis was explored in Chapter 3 of my thesis. I first performed biochemical characterization of the prism-extracted matrix and further deciphered the whole set of prism-associated proteins by proteomics. This proteome is made of hundreds of proteins. In silico analysis showed the diversity of molecular functions required for constructing ‘simple’ prisms and pointed out the key-role played by proteins with low complexity domains. Furthermore, I characterized more specifically one 11KDa protein that I named accripin11, to understand its role in the prism formation process. Finally, we developed a novel technique in biomineralization that allowed localizing accripin11 on the surface of the shell prisms with a nanometric resolution. This technique relies on atomic force microscopy scanning performed with a tip functionalized with an antibody that specifically targets accripin11.In summary, my work contributes to the advancement of imaging tools to observe complex biomineral structures and to better understand the distribution of organics in these structures. It represents one of the few attempts to bridge the gap between biology and physics in biomineralization studies.