Silicanin-1 is a conserved diatom membrane protein involved in silica biomineralization

Abstract

BackgroundBiological mineral formation (biomineralization) proceeds in specialized compartments often bounded by a lipid bilayer membrane. Currently, the role of membranes in biomineralization is hardly understood.ResultsInvestigating biomineralization of SiO2 (silica) in diatoms we identified Silicanin-1 (Sin1) as a conserved diatom membrane protein present in silica deposition vesicles (SDVs) of Thalassiosira pseudonana. Fluorescence microscopy of GFP-tagged Sin1 enabled, for the first time, to follow the intracellular locations of a biomineralization protein during silica biogenesis in vivo. The analysis revealed incorporation of the N-terminal domain of Sin1 into the biosilica via association with the organic matrix inside the SDVs. In vitro experiments showed that the recombinant N-terminal domain of Sin1 undergoes pH-triggered assembly into large clusters, and promotes silica formation by synergistic interaction with long-chain polyamines.ConclusionsSin1 is the first identified SDV transmembrane protein, and is highly conserved throughout the diatom realm, which suggests a fundamental role in the biomineralization of diatom silica. Through interaction with long-chain polyamines, Sin1 could serve as a molecular link by which the SDV membrane exerts control on the assembly of biosilica-forming organic matrices in the SDV lumen.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-017-0400-8) contains supplementary material, which is available to authorized users.

Siliplant1 (Slp1) protein precipitates silica in sorghum silica cells

“…At the end of R1, R3, and R5, we found an RXL domain. This domain acts as recognition site for unknown proteases that cleave at the C-terminus of the leucine residue of the RXL domain in many bio-silica associated proteins in diatoms (Kröger et al ., 1999; Wenzl et al ., 2008; Scheffel et al ., 2011; Kotzsch et al ., 2017). Despite these common features, Slp1 does not show sequence similarity with any protein known to be involved in bio-mineralization.…”

“…Binding of anti-Peptide-1 antibody in the boundary of dead silica cells of mature leaves suggests that as Slp1 templates the silica precipitation, it is caught inside the silica structure. Silicanin-1, a biosilica associated protein from T. pseudonana gets embedded inside biosilica structure and is accessible to anti-silicanin-1 antibody (Kotzsch et al ., 2017). Similarly, anti-Peptide-1 antibody may also have access to the epitope remains on the surface of the deposited silica in silica cells.…”

“…Silicification is widespread among living beings from unicellular microbes to highly evolved multicellular organisms (Perry, 2003). Several bio-silica associated proteins have been reported, for example, silaffins (Kröger et al ., 1999; Poulsen & Kröger, 2004), silacidins (Wenzl et al ., 2008) and silicanin-1 (Kotzsch et al ., 2017) from diatoms; and silicateins (Shimizu et al ., 1998) and glassin (Shimizu et al ., 2015) from sponges. Among plants, a short peptide derived from an inducible proline-rich protein precipitates silica in vitro .…”

Mating type specific transcriptomic response to sex inducing pheromone in the pennate diatomSeminavis robusta

“…Accordingly, we observed downregulation of genes known to be important for silica cell wall formation after treatment with SIP ( Figure 3A). These include two silicic acid transporters: membrane proteins that are involved in the uptake of silicic acid from the environment 52 ; two silicanins: proteins embedded in the SDV membrane 53 ; as well as four frustulins: proteins which are found in the organic casing surrounding the cell wall 54 . Moreover, four genes making up various subunits of V-type ATPase complexes were significantly downregulated in both species upon treatment with SIP.…”

Distinct genome‐wide alternative polyadenylation during the response to silicon availability in the marine diatom Thalassiosira pseudonana

“…Previous studies have revealed several key proteins and components closely associated with diatom cell-wall formation, including cingulins (Scheffel et al, 2011), silacidins (Wenzl et al, 2008), silaffins (Kr€ oger et al, 1999), silicanin (Kotzsch et al, 2017), and long-chain polyamines (Kr€ oger et al, 1999(Kr€ oger et al, , 2000. In particular, cingulins, which were initially discovered in the model diatom species T. pseudonana (Scheffel et al, 2011), are components associated with the girdle band silicification.…”