Polycationic Peptides from Diatom Biosilica That Direct Silica Nanosphere Formation

TLDR

Diatom cell walls serve as a paradigm for controlled nanostructured silica production, yet the ambient‑temperature, high‑rate biosilicification mechanisms remain unclear, partly due to the covalently modified lysine‑lysine motifs in silaffins. Polycationic peptides called silaffins, isolated from diatom cell walls, rapidly form silica nanosphere networks within seconds in silicic acid, with their activity driven by a first lysine bearing a 6–11 repeat polyamine of N‑methyl‑propylamine and a second lysine that is ɛ‑N,N‑dimethyl‑lysine, modifications that drastically enhance silica precipitation.

Abstract

Diatom cell walls are regarded as a paradigm for controlled production of nanostructured silica, but the mechanisms allowing biosilicification to proceed at ambient temperature at high rates have remained enigmatic. A set of polycationic peptides (called silaffins) isolated from diatom cell walls were shown to generate networks of silica nanospheres within seconds when added to a solution of silicic acid. Silaffins contain covalently modified lysine-lysine elements. The first lysine bears a polyamine consisting of 6 to 11 repeats of the N -methyl-propylamine unit. The second lysine was identified as ɛ - N,N -dimethyl- lysine. These modifications drastically influence the silica-precipitating activity of silaffins.