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Abstract
Plants have two endosymbiotic organelles, chloroplast and mitochondrion. Although they have their own genomes, proteome assembly in these organelles depends on the import of proteins encoded by the nuclear genome. Previously, we elucidated the general design principles of chloroplast and mitochondrial targeting signals, transit peptide, and presequence, respectively, which are highly diverse in primary structure. Both targeting signals are composed of N-terminal specificity domain and C-terminal translocation domain. Especially, the N-terminal specificity domain of mitochondrial presequences contains multiple arginine residues and hydrophobic sequence motif. In this study we investigated whether the design principles of plant mitochondrial presequences can be applied to those in other eukaryotic species. We provide evidence that both presequences and import mechanisms are remarkably conserved throughout the species. In addition, we present evidence that the N-terminal specificity domain of presequence might have evolved from the bacterial TAT (twin-arginine translocation) signal sequence.
Highlights
The mitochondrion and chloroplast are thought to have evolved from a-proteobacteria and cyanobacteria, respectively, by endosymbiosis (Gray, 2012)
We showed that the substitution of multiple arginines with alanines in the presequence leads to protein import into chloroplasts (Lee et al, 2019)
We replaced the first two or last three arginine residues of human mitochondrial fumarate hydratase (hFH)[N80] with alanine residues to produce hFH[N80][2R/2A] or hFH[N80][3R/3A], respectively (Figure 1A). These mutant presequences were fused to GFP, and the resultant constructs were introduced into protoplasts. hFH[N80] [2R/2A] supported protein import into mitochondria, as indicated by the colocalization of GFP with MitoTracker red in Arabidopsis protoplasts
Summary
The mitochondrion and chloroplast are thought to have evolved from a-proteobacteria and cyanobacteria, respectively, by endosymbiosis (Gray, 2012). The Nterminal specificity domain of the presequence shows a high degree of similarity to the TAT signal sequence with respect to its sequence motifs. It is still not understood how presequences of mitochondrial proteins evolved during the endosymbiotic conversion of a-proteobacteria to mitochondria. We examined 1) whether the mechanism by which plant presequences confer mitochondrial targeting specificity applies to presequences of animal and fungal proteins, and 2) whether TAT signal sequences can be functional substitutes for the N-terminal specificity domain of mitochondrial presequences
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