Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation

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.

Intrinsically disordered proteins and biomineralization

“…Silaffins, for example, are protein constituents of biosilica, playing an active role in silica formation. These small proteins with numerous phosphoserine repeats self-assemble via electrostatic interactions; a prerequisite for biosilica formation [110,111]. SM50, from the mineralized larval of sea urchin spicules, contains C-type lectin and IDPs repeat domains.…”

1H-detected solid-state NMR of proteins entrapped in bioinspired silica: a new tool for biomaterials characterization

“…In vitro , large amounts of proteins can be properly encapsulated in silica by simply mixing cationic catalyst with the silicic acid and the protein itself7 or, to increase the immobilization yield, the protein can be fused to a biosilica-promoting peptide891011121314. The materials obtained by such natural processes can be easily tuned into different morphologies by the use of slight perturbations of the experimental conditions1015, and can be easily endowed with peculiar chemical properties, such as fluorescence or catalytic activity by the incorporation of proteins9. In turn, proteins that are entrapped in a silicic matrix become more stable and easily reusable1617.…”

Biosilica and bioinspired silica studied by solid-state NMR

“…To better understand and characterize key elements in biosilica formation and their functional pathway SSNMR studies of peptides such as R5 and LKα free and bound to silica were carried out. R5 (SSKKSGSYSGSKGSKRRIL) is a short derivative of silaffin from C. fusiformis lacking PTM that catalyzes silica formation in vitro [44,147,33]. Some studies indicated that the R5 peptide self-assembles and forms aggregates that provide templates for silica formation [148][149][150], while others found no evidence of self-assembly and hypothesize that silica formation occurs through salt-bridges.…”

“…To fruitfully put this lesson to use, bioinspired matrices have been developed such as biosilica. The definition of biosilica, just like that of biomaterials in general, varies between silica/materials that are formed in nature by living organisms (aka biogenic materials, which are more appropriately referred to as biosilica) and silica/materials that is synthesized in the lab by bioinspired reactions, using molecules from the living organism or their derivatives [32][33][34], to mimic the "natural conditions" (bio-inspired silica). Hereon, for simplicity we will refer to either species as biosilica, as the origin of the material is clearly described along with the experimental details.…”