Polycationic peptides from diatom biosilica that direct silica nanosphere formation

Diatom cell walls are regarded as a paradigm for controlled production of n anostructured silica, but the mechanisms allowing biosilicification to proc eed at ambient temperature at high rates have remained enigmatic. A set of polycationic peptides (called silaffins) isolated from diatom cell walls we re shown to generate networks of silica nanospheres within seconds when add ed to a solution of silicic acid. Silaffins contain covalently modified Lys ine-Lysine elements. The first Lysine bears a polyamine consisting of 6 to 11 repeats of the N-methyl-propylamine unit. The second Lysine was identifi ed as epsilon-N,N-dimethyl-lysine. These modifications drastically influenc e the silica-precipitating activity of silaffins.