The biosilica produced by diatoms is composed of porous nano- and micropatterned amorphous silica and associated biomolecules. In respect to the latter, important members were identified in the model diatom Thalassiosira pseudonana, which can be distinguished by their solubility in a mildly acidic solution of ammonium fluoride. In our project we will focus on Silaffins, important proteins of the soluble fraction, and on Cingulins, a recently identified protein family of the insoluble fraction. Both protein families show a specific localization either in the valve (Silaffins) or the girdle band (Cingulins). In our project we aim to identify the signals responsible for the specific localization of Silaffins and Cingulins, including the expression control during the different cell cycle phases.
Over the last years important observations have been made helping to understand the mechanisms of intracellular protein targeting in diatoms. In respect to biosilica-associated biomolecules, the proteins are expected to be synthesized at the ER and further targeted to a so-called SDV (silica deposition vesicle), in which silica is polymerized. However, it is yet unknown if the proteins use the canonical pathway (from ER to the Golgi to SDV) or are being targeted bypassing the Golgi-apparatus. In cooperation with SP3 (Andrej Shevchenko) we will investigate the targeting route in a proteomic approach.
From our project we will therefore learn (i) which signals and cell cycle phases are important for specific targeting of biomolecules, and (ii) which intracellular routes these proteins use to reach their specific localization.