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Priority Programme 1569: "Generation of multifunctional inorganic materials by molecular bionics"

 

Genetically controlled self-assembly of inorganic-bioorganic hybrid structures: From sponge genes to layered functional materials


 

Dr. Matthias P. Wiens, Universitätsmedizin der Johannes Gutenberg-Universität Mainz;Institut für Physiologische Chemie, Duesbergweg 6, 55128 Mainz, 

Professor Dr. Wolfgang Tremel, Johannes Gutenberg-Universität Mainz; Fachbereich 09 - Chemie, Pharmazie u Geowissenschaften, Institut für Anorganische Chemie und Analytische Chemie, Duesbergweg 10-14, 55128 Mainz,
 

Conventional processing techniques mostly exclude the preparation of multifunctional silica- and other metal(loid) oxide-based materials with an expanded property spectrum. Therefore, the potential of those bionic approaches is huge that apply the principles of gene-regulated biosilicification for the synthesis of such materials at ambient conditions. Enzymatic, gene-regulated silica metabolism is only known to exist in the animal phylum Porifera (sponges) and, hence, is very promising for the design of inorganic-bioorganic hybrids in the field of molecular bionics. During the last decade, groundbreaking research of poriferan biosilicification around our consortium has considerably increased knowledge of many aspects of the matri­ces/templates and biocatalysts/enzymes involved. Biosilica formation is initiated by the intracellular assembly of filaments that are localized within siliceous skeletal elements (spicules) and determine biosilica-morpho­genesis. The filaments predominantly consist of the enzyme silicatein and the scaffold protein silintaphin. Silicatein templates and catalyzes polymerization of amorphous silica nanospheres from soluble precursors that, subsequently, biosinter to concentric layers. Concurrently, bifunctional silintaphin directs the assembly of filaments and facilitates the catalytic activity of silicatein. The resulting spicules have a genetically determined morphology, with laminate architecture, and carry the proteinaceous scaffold embedded within biosilica. Biosilica has the extraordinary properties of advanced materials (mechanical, optical, physiological), far exceeding current human engineering capabilities. Based on silicatein and silintaphin, low energy biocatalytic synthesis ("green chemistry") has finally become accessible. Hence, many bioinspired biocatalytic routes were taken for synthesis of not only biosilica but also other, nonbiological materials, consequently paving the way for the bionic approaches of the present proposal. Indeed, poriferan biosilicification has been characterized to a level at which the majority of genes and proteins involved have not only be identified but are also available for in vivo and in vitro application in the form of genetic constructs (plasmids and cDNA libraries) and recombinant proteins (enzymes, scaffold proteins, and chimeras). Based on the genetic and biochemical manipulability of the poriferan system, our bionic approach aims to hybridize bioengineered enzymes and scaffold proteins with non-biogenic nanoparticles as building blocks to design layered inorganic-bioorganic structures with novel property combinations. These materials will be formed in vivo (via sponge cell culture) and in vitro (via affinity-tagged and/or bifunctional chimeras; above all, silicatein and silintaphin). Then, the formation mechanisms (in particular self-assembly and biosintering) and structures/morphologies will be characterized as well as the physico-chemical properties. In this context, attention will also be directed to the inorganic-bioorganic interfaces and the array of the bioorganic and inorganic building blocks by applying high resolution techniques.

 

 

Fig. 1. The axial filament of S. domuncula spicules. (A) Sponge tissue cross-section with a spicule comprising in its center the axial canal (ac) that harbors the axial filament (af). (B) Spicule with its terminal knob (kn) and subterminal collar (co). (C) Partially HF-dissolved spicule (sp), showing the protruding axial filament (af). (D) Bundle of axial filaments from HF-dissolved spicules. (E) Isolated filaments, incubated with TEOS, producing abundant biosilica clusters (sc). (F) Higher magnification of biosilica clusters. B-F, SEM; A, TEM.

 

Fig. 2. Synthetic axial filaments and spicules. (A) Biomimetic formation of filaments through silicatein - silintaphin interaction in vitro. (B) Biomimetic in vitro formation of synthetic spicules after silintaphin interaction with silicatein immobilized on γ-Fe2O3 nanoparticles. (C) Incubation of silicatein and silintaphin with TiBALDH resulted in synthesis and assembly of biotitania nanoparticles. (D) Assembly of silica nanoparticles in the presence of silicatein and silintaphin. Scale bars, 1 μm (A,B); 500 nm (C,D).