Polycationic Peptides from Diatom Biosilica That Direct Silica Nanosphere Formation

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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.