FRUSTULINS - DOMAIN CONSERVATION IN A PROTEIN FAMILY ASSOCIATED WITH DIATOM CELL-WALLS

The outstanding feature of a diatom is the species-specific design and ornamentation of the silica-based cell wall, termed frustulum. A new frustulum is shaped in a specialized organelle (silica deposition vesi cle) and secreted. Proteins in the lumen of this organelle may control the biomineralization process and are likely to remain associated wit h the mature cell wall. Therefore a study of the structures of protein s associated with the diatom cell wall was initiated. The complete pri mary structures of three cell wall proteins (denoted as frustulins) ha ve been determined. In addition, partial amino acid sequences from two more cell wall components were obtained. From these data, a highly co nserved domain has been identified as a common building block of diato m cell wall proteins that is repeated several times per polypeptide ch ain together with polyproline/hydroxyproline or polyglycine spacers. A ll frustulins characterized so far, are synthesized as preproteins wit h a novel type of N-terminal presequence.