Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation.

Christian Becker,Carolin Lechner

doi:10.3390/md13085297

Christian Becker, Carolin Lechner

Open Access

https://doi.org/10.3390/md13085297

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Abstract

Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typically occur as complex posttranslationally modified variants and are directly involved in the silica deposition process in diatoms. However, even in vitro silaffin-based peptides alone, with and without posttranslational modifications, can efficiently mediate biomimetic silica precipitation leading to silica material with different properties as well as with encapsulated cargo molecules of a large size range. In this review, the biomineralization process of silica in diatoms is summarized with a specific focus on silaffins and their in vitro silica precipitation properties. Applications in the area of bio- and nanotechnology as well as in diagnostics and therapy are discussed.

Highlights

Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research
The currently available knowledge serves as a basis for biomimetic silica formation processes leading to functionalized silica for applications in biotechnology with special emphasis on silica decorated with sensitive cargo molecules
Silaffins are proteins combining both polycationic and polyanionic functionalities in one molecule that fulfill a substantial function in the molecular process of silica formation in diatoms

Summary

Silicon in Nature

Silicon is the second most abundant element in the Earth’s crust and associated with oxygen, silicates and silica (SiO2) constitute the most common compounds in the lithosphere [1]. Silicon is not considered an essential element but as advantageous for plants since it is beneficial for plant growth, provides structural support for cell walls and mediates resistance of plants to biotic and abiotic stress [11,12,13]. Silicon is essential for a couple of specific biota including diatoms, siliceous sponges, radiolaria and silicoflagellates. These organisms require silicon for the production of siliceous structures, ranging from frustules, spicules and scales to various species-specific elaborate forms [14]. Since silicon-deficiency effects diatom growth and cell wall formation and interferes with metabolic processes [15], its essential role in diatoms is clearly confirmed. The currently available knowledge serves as a basis for biomimetic silica formation processes leading to functionalized silica for applications in (nano-) biotechnology with special emphasis on silica decorated with sensitive cargo molecules

Diatom Biology and Cell Cycle

Organic Constituents of Diatom Cell Walls and Their Role in Silica Formation

Silaffin Proteins and Peptides

Chemical and Mechanistic Aspects of Silica Formation

LCPA-Induced Silica Formation Based on Phase Separation

Silaffin-Induced Silica Precipitation

Biotechnological Applications of Silica

Synthetic Silica Materials

Diatomaceous Earth and Biogenic Diatom Silica

Biomimetic Silica

Biotechnological Applications Based on Biomimetic Silica

Outlook