Gerhard Lehmann

Biomineralization in diatoms: Characterization of novel polyamines associated with silica

Pattern formation during silica biomineralization in diatoms appears to depend on long‐chain polyamines as well as proteins covalently modified with polyamines (silaffins). Recently, the complete genome of the diatom Thalassiosira pseudonana has been sequenced making this species an attractive model organism for future studies on biomineralization. Mass‐ and NMR‐spectroscopic analysis of the long‐chain polyamines from this diatom species reveals the existence of a complex population with as yet unknown structural features. These include complex methylation patterns, different attachment moieties as well as the existence of quaternary ammonium functionalities.

Silica Pattern Formation in Diatoms: Species-Specific Polyamine Biosynthesis

Diatoms are eukaryotic, unicellular algae that are well known for the intricate architecture of their silica‐based cell walls. Species identification is mainly based on variations of their hierarchically organized silica structures. Particularly striking silica frameworks are found among diatoms that belong to the genus Coscinodiscus. Recent work indicates an important role for long‐chain polyamines in guiding silica precipitation as well as in silica‐pattern formation. Here we demonstrate that polyamines, even if isolated from closely related diatom species, exhibit substantial structural differences. Structural variations include the overall chain length, the degree of methylation, positions of secondary amino functionalities, and, unexpectedly, site‐specific incorporation of a quaternary ammonium functionality. These findings support a specific role for polyamines in creating silica nanostructures.

Letter to the Editor: 1H, 13C and 15N sequence-specific resonance assignment of the PSCD4 domain of diatom cell wall protein pleuralin-1

Pleuralins (formerly HEPs), a previously describeddiatom protein family (Kroger et al., 1997), are in-volved in the cell cycle dependent morphogenesisof the silica cell wall consisting of two overlappinghalf-shells (thecae, Kroger and Wetherbee, 2000).They are located at the inner surface of the terminalelements (pleural bands) of the epitheca. All mem-bers of the pleuralin family contain a proline-richdomain followed by 3–5 conserved so-called PSCDdomains of 87 or 89 amino acid residues, respec-tively, rich in proline (22%), serine (11%), cysteine(11%), and aspartate (9%). They contain 10 cysteineresidues at exactly the same positions forming disul-phide bridges and show 73–91% sequence identity toeach other. Pleuralins are tightly incorporated withinthe silica scaffold, imperishable to EDTA and SDStreatment, but extractable with anhydrous hydrogenfluoride (HF). It seems, therefore, likely that they areconnected to the cell wall by covalent linkage to thesilanol groups (SiOH) of the silica surface by Si–O–C bonds or by crosslinking with HF-labile glycosidebonds (Kroger et al., 1997). Possible posttranslationalmodifications have not been analysed so far. In thisstudy we present sequence-specific assignment of theNMR signals of a fragment of pleuralin-1 (formerlyHEP200; amino acids 366–468) of

KOMPLEX-BLDG. VON CO(II) MIT HALOGENIDEN IN WAESSRIGER LOESUNG

Die spektrophotometrische Untersuchung des Komplexgleichgewichts zwischen Co(H2O)a und Halogeniden zeigte die Anwesenheit von CoXa′ und der Innerspharkomplexe Co(H2O)5X+ und Co(H2O)4X2 als Zwischenstufen (X = Cl, Br, J).