Possible role of ubiquitin in silica biomineralization in diatoms:identification of a homologue with high silica affinity

Abstract

In diatom silicon biomineralization peptides are believed to play a role in silica precipitation and the consequent structure direction of the cell wall. Characterization of such peptides should reveal the nature of this organic-inorganic interaction, knowledge that may eventually well be used to expand the existing range of artificial silicas ("biomimicking"). Biochemical studies on Navicula pelliculosa revealed a set of proteins, which have a high affinity for a solid silica matrix; some were only eluted from the matrix when SDS-denaturation was applied. One of the proteins with an affinity for silica, about 8.5 kDa, is shown to be a homologue of ubiquitin on the basis of its N-terminal amino acid sequence; ubiquitin itself is a highly conserved 8.6 kDa protein that is involved in protein degradation. This finding is in line with a model of silica biomineralization in diatoms that implies the removal of templating polypeptides when pores in the growing cell wall develop. Western blotting with specific anti-ubiquitin antibodies confirmed cross-reactivity. Immunocytochemical localization of ubiquitin indicates that it is present along the diatom cell wall and inside pores during different stages of valve formation. (C) 2003 Elsevier Science B.V. All rights reserved