earticle

영어

The discovery of the principle molecules involved in biosilification in sponges (silicateins) brings out a new paradigm for silica synthesis at environmentally benign conditions. However, silicatein has been expressed in low level and inclusion body formation when expressed in E. coli. Therefore, there have been many alternative strategies attempted to overcome this limitation. Silicatein has high sequence identity and similarity with that of cathepsin L in which the cysteine at the active site is replaced by serine in silicatein. We hypothesized that a cathepsin L-like protein with a high sequence identity to silicatein has silica condensing activity or can be evolved to a protein capable of silica deposition by changing some residues. In order to investigate this, we obtained hypothetical cathepsin-like protein (CAT) from Nematostella vectensis which displays 55 % identity and 75% similarity with mature silicatein alpha (SIL) of Suberites domuncula from a BLAST-based search of protein sequence. This protein expressed in E.coli displayed not only gelatinolytic activity but also silica condensing activity. The cysteine residue among catalytic triad of CAT was changed into serine residue, producing a mutant, C27S-CAT. There were no significant differences in enzymatic activities of proteolysis and silica deposition between CAT and C27S-CAT. Whereas the expression of CAT in E. coli was not stable due to its proteolytic activity, the solubility of CAT was increased compared to that of SIL. In conclusion, a predicted protein, cathepsin L-like protein from N. vectensis was capable of silica deposition and it could be evolved to more soluble and available biosilica forming protein.