Final Report Summary - BIOSILICA (From gene to biomineral: Biosynthesis and application of sponge biosilica)
Biomineralization has attracted multidisciplinary scientific attention, not only because this process touches the interface between the organic world and the inorganic world but also because it offers fascinating bio-inspired solutions in the fields of nanotechnology and biomedicine. One group of animals has the necessary genetic and enzymatic toolkit to control biomineralization: siliceous sponges (Porifera). Based on pioneering discoveries in poriferan molecular biology and physiological chemistry, biosilicification has been brought into the focus of basic and applied research. In this ERC project, using a unique blend of cutting-edge techniques in molecular/structural biology, biochemistry, bioengineering, and material sciences, a comprehensive analysis of the biomineralization process in the siliceous sponges, from gene level to the hierarchically ordered biosilica structures of increasing complexity, has been approached. The essential genes/cDNAs involved in biosilicification have been isolated and characterized. In addition to silicatein (different isoforms), various silicatein interactors (silintaphins), as well as proteins (aquaporins, nodulin-like proteins, etc.) involved in the maturation/ageing of the initially formed soft biosilica product to a solid material have been identified. The posttranslational modifications of silicatein, as well as the function of the silintaphins in the assembly of the silicatein axial filaments and in spicule formation have been elucidated. The mechanism of the self-cleavage of the silicatein precursor, leading to the formation of the enzymatically active and assembly- competent mature silicatein has been explored. The sequential expression of the sponge genes involved in the biosilicification have been demonstrated using the sponge 3D cell/tissue culture system (primmorphs). The morphology and composition of the inorganic-organic biosilica hybrid material and the process of bio-sintering have been investigated using advanced methods. Further steps in biosilica formation such as the process of syneresis (expulsion of reaction water) have been described for the first time. The function of silicasomes as well as cellular and molecular factors involved in the spatio-temporal control of spicular morphogenesis, such as interacting cells, formation of cell evaginations and regulatory factors have been elucidated. The self-healing properties of biosilica via entrapped silicatein molecules have been demonstrated. Moreover, we were the first to demonstrate that sponges which have both a light generating system (luciferase) and a light perception system (cryptochrome) are able to flash “in vivo”, indicating the existence of a nerve-like system in sponges that uses the spicules as light transmitters. In addition, a system controlling the day-night rhythm in sponges (nocturnin) has been discovered. We also succeeded to introduce specific mutations into the silicatein protein, allowing the dissection of the function of the protein and the generation of light transmitting biosilica fibers. The process of biosilica formation in the siliceous sponges, elucidated in this project, is the first biomineralization process that that is now understood from the gene level up to the organization of the 3D skeletal architectures. Further we have demonstrated that all principle bomineralization processes in animals – biosilicification, biocalcification and bone hydroxyapatite –, from the evolutionary oldest, still extant (siliceous sponges) up to humans, are mediated by enzymes and are using the same genetic blueprint, a discovery that has revolutionized our understanding of biomineral formation. The elucidation of the molecular mechanism of enzymatic biosilica formation also allowed a new understanding of the mechanism of human bone mineral formation, resulting in a paradigm change, and the development of the first morphogenetically active inorganic biomaterials for repair of bone and cartilage but also for artificial blood vessels.