Molecular machines encoded by bacterially-derived multi-domain gene fusions that potentially synthesize,N-methylate and transfer long chain polyamines in diatoms

Abstract

a b s t r a c tSilica glass formation in diatoms requires the biosynthesis of unusual, very long chain polyamines (LCPA) composed of iterated aminopropyl units. Diatoms processively synthesize LCPA, N-methylate the amine groups and transfer concatenated, N-dimethylated aminopropyl groups to silaffin proteins. Here I show that diatom genomes possess signal peptide-containing gene fusions of bacterially-derived polyamine biosynthetic enzymes S-adenosylmethionine decarboxylase (AdoMetDC) and an aminopropyltransferase, sometimes fused to a eukaryotic histone N-methyltransferase domain, that potentially synthesize and N-methylate LCPA. Fusions of similar, alternatively configured domains but with a catalytically dead AdoMetDC and in one case a Tudor domain, may N-dimethylate and transfer multiple aminopropyl unit polyamines onto silaffin proteins.

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

“…Each of the four species contain multiple APT gene copies, including the two phylogenetically diverged clades hypothesized by Anthony (2011) to be involved in long-chain polyamine synthesis (Fig. 5B).…”

“…The pathway for long-chain polyamine synthesis is hypothesized to involve spermidine synthase-like genes (Frigeri et al 2006;Knott et al 2007;Knott 2009), or more generally aminopropyl transferases (APT; Ikeguchi et al 2006). APT genes are part of a multicopy gene family in diatoms, which includes two phylogenetically distinct groups of genes encoding proteins proposed to be responsible for long-chain polyamine synthesis and modification of silaffin proteins with polyamine side chains (Anthony 2011). In T. pseudonana, several of the APT genes proposed to be involved in longchain polyamine synthesis due to their predicted protein domain structure (Anthony 2011) are upregulated by silicic acid and iron starvation, suggesting a potential role in the observed response of the frustule to iron starvation (Mock et al 2008).…”

“…APT genes are part of a multicopy gene family in diatoms, which includes two phylogenetically distinct groups of genes encoding proteins proposed to be responsible for long-chain polyamine synthesis and modification of silaffin proteins with polyamine side chains (Anthony 2011). In T. pseudonana, several of the APT genes proposed to be involved in longchain polyamine synthesis due to their predicted protein domain structure (Anthony 2011) are upregulated by silicic acid and iron starvation, suggesting a potential role in the observed response of the frustule to iron starvation (Mock et al 2008). Chitin is another compound embedded within the frustule of T. pseudonana (Brunner et al 2009) and likely other members of the Thalassiosirales lineage.…”

Polyamines in Eukaryotes, Bacteria, and Archaea

“…It is thought that the LCPAs participate in the condensation of silicic acid to form silica through a phase separation process that also involves proteins that are modified by a separate class of LCPAs linked through a lysine residue (52,53). From genome analysis, it appears likely that the diatom LCPAs are synthesized by a set of horizontally acquired bacterial AdoMetDC-aminopropyltransferase fusion proteins occasionally containing methyltransferase (SET) domains (54). LCPAs that are similar but lack N-methylation are found in glass sponges where they may also be involved in biosilica formation (55).…”

A family of diatom-like silicon transporters in the siliceous loricate choanoflagellates

“…Stramenopile-derived genes are thought to be unusually frequent in M. brevicollis [57], including genes linked with the evolution of multicellularity [61]. Diatoms are believed to have gained some of their biosilicification machinery (related to longchain polyamine formation) from LGT [62] in addition to other diatom-specific metabolic pathways [58].…”