Nanopatterned protein microrings from a diatom that direct silica morphogenesis

Abstract

Diatoms are eukaryotic microalgae that produce species-specifically structured cell walls made of SiO 2 (silica). Formation of the intricate silica structures of diatoms is regarded as a paradigm for biomolecule-controlled self-assembly of three-dimensional, nano-to microscale-patterned inorganic materials. Silica formation involves long-chain polyamines and phosphoproteins (silaffins and silacidins), which are readily soluble in water, and spontaneously form dynamic supramolecular assemblies that accelerate silica deposition and influence silica morphogenesis in vitro. However, synthesis of diatom-like silica structure in vitro has not yet been accomplished, indicating that additional components are required. Here we describe the discovery and intracellular location of six novel proteins (cingulins) that are integral components of a silica-forming organic matrix (microrings) in the diatom Thalassiosira pseudonana. The cingulin-containing microrings are specifically associated with girdle bands, which constitute a substantial part of diatom biosilica. Remarkably, the microrings exhibit protein-based nanopatterns that closely resemble characteristic features of the girdle band silica nanopatterns. Upon the addition of silicic acid the microrings become rapidly mineralized in vitro generating nanopatterned silica replicas of the microring structures. A silica-forming organic matrix with characteristic nanopatterns was also discovered in the diatom Coscinodiscus wailesii, which suggests that preassembled protein-based templates might be general components of the cellular machinery for silica morphogenesis in diatoms. These data provide fundamentally new insight into the molecular mechanisms of biological silica morphogenesis, and may lead to the development of self-assembled 3D mineral forming protein scaffolds with designed nanopatterns for a host of applications in nanotechnology.biomineralization | GFP | silica deposition vesicle | bioinformatics

Frustule‐related gene transcription and the influence of diatom community composition on silica precipitation in an iron‐limited environment

“…Silaffins, silacidins, and cingulins (Kroger et al 1999;Wenzl et al 2008;Scheffel et al 2011) are proteins required for silica precipitation. These protein families contain common amino acid motifs (e.g., lysine-rich), but their limited nucleotide sequence conservation complicates gene identification and characterization across different species.…”

Competition between Silicifiers and Non-silicifiers in the Past and Present Ocean and Its Evolutionary Impacts

“…The polymerization rate in these in vitro experiments, and therefore the nanoscale patterning (including formation of plates and pores), has been shown to be influenced by proteins including silaffins (Kröger et al, 2002), silacidins (Wenzl et al, 2008), and long-chain polyamines (LCPAs; Kröger et al, 2000;Sumper and Kröger, 2004). Some unique frustule structures are marked out by them containing specific biosilica-related proteins, such as cingulins that form the girdle bands linking the two valves of the frustule (Scheffel et al, 2011). The number, size and shape of girdle bands vary between diatom species, and this may be connected to variations in cingulin repertoires.…”

Synthetic Morphogenesis

“…For example, diatom cell walls have an array of astonishingly uniform pores, with promising nanotechnology applications ranging from molecular sieves to photonics (Gordon et al 2009). Many of the molecular details about diatom cell wall biogenesis are known, including the protein scaffolds involved in silicate condensation and large-scale patterning (Kröger and Poulsen 2008;Scheffel et al 2011), and yet we are still unable to alter pore size and arrangement in any directed fashion. In fact, none of the reported genetic modifications to the cell wall machinery resulted in any morphological changes at all!…”