Protease-Mediated Hydrolysis and Condensation of Tetra- and Trialkoxysilanes - Bio-Inspired Silicon-Based Materials - page 27

Silaffin-1A 1
NH 2 SSK K S G S Y S G S K G S K COOH

OH

NH N N NH

NH NH

n = 4-9

n=4-9

N N

N

N

Silaffin-1A 2
NH 2

SSK K S G S Y S G Y S T K K S GSK COOH

HO

N

NH

NH N

NH

NH

n = 4-9

n=4-9

N

N

N

N

Fig. 3.1 The chemical structures of silaffin-1A 1 and silaffin-1A 2 . The post-translationally modi-
fied lysine residues contribute to the structure directing activity of the silaffins [ 2 , 9 ]

The silica precipitating action of silaffin-1A is dependent on these post-trans-
lationally modified lysine residues [ 2 ]. Silica precipitation assays using silaffin
preparations with a metastable silicic acid solution produced silica within seconds
[ 1 ]. The silaffins co-precipitated with silica suggesting that they act in a structure
directing role.
The silacidins on the other hand are rich in aspartate/glutamate and phosphorylated
serine residues that make them anionic at neutral pH [ 3 ]. These peptides produced
silica, when combined with polyamines, in a concentration dependent manner and it
has been hypothesized that these proteins are the biological anion required to direct
that precipitation of silica in vivo .