A single peroxisomal targeting signal mediates matrix protein import in diatoms.

Peroxisomes are single membrane bound compartments. They are thought to be present in almost all eukaryotic cells, although the bulk of our knowledge about peroxisomes has been generated from only a handful of model organisms. Peroxisomal matrix proteins are synthesized cytosolically and posttranslationally imported into the peroxisomal matrix.

Making new out of old: recycling and modification of an ancient protein translocation system during eukaryotic evolution. Mechanistic comparison and phylogenetic analysis of ERAD, SELMA and the peroxisomal importomer.

At first glance the three eukaryotic protein translocation machineries--the ER-associated degradation (ERAD) transport apparatus of the endoplasmic reticulum, the peroxisomal importomer and SELMA, the pre-protein translocator of complex plastids--appear quite different. However, mechanistic comparisons and phylogenetic analyses presented here suggest that all three translocation machineries share a common ancestral origin, which highlights the recycling of pre-existing components as an effective evolutionary driving force. Editor's suggested further reading in BioEssays ERAD ubiquitin ligases Abstract.

ERAD components in organisms with complex red plastids suggest recruitment of a preexisting protein transport pathway for the periplastid membrane.

The plastids of cryptophytes, haptophytes, and heterokontophytes (stramenopiles) (together once known as chromists) are surrounded by four membranes, reflecting the origin of these plastids through secondary endosymbiosis. They share this trait with apicomplexans, which are alveolates, the plastids of which have been suggested to stem from the same secondary symbiotic event and therefore form a phylogenetic clade, the chromalveolates. The chromists are quantitatively the most important eukaryotic contributors to primary production in marine ecosystems.

The physical and functional borders of transit peptide-like sequences in secondary endosymbionts.

Background: Plastids rely on protein supply by their host cells. In plastids surrounded by two membranes (primary plastids) targeting of these proteins is facilitated by an N-terminal targeting signal, the transit peptide. In secondary plastids (surrounded by three or four membranes), transit peptide-like regions are an essential part of a bipartite topogenic signal sequence (BTS), and generally found adjacent to a N-terminally located signal peptide of the plastid pre-proteins.

New mechanistic insights into pre-protein transport across the second outermost plastid membrane of diatoms.

Chromalveolates like the diatom Phaeodactylum tricornutum arose through the uptake of a red alga by a phagotrophic protist, a process termed secondary endosymbiosis. In consequence, the plastids are surrounded by two additional membranes compared with primary plastids. This plastid morphology poses additional barriers for plastid-destined proteins, which are mostly nucleus-encoded.