Comparison of PTS1 motifs between D. rerio and H. sapiens: To depict the difference in the average abundance of amino acids at different positions of the PTS1 in fish (A) and humans (B), we selected proteins from each species, which were predicted to harbour a PTS1 (Neuberger et al., 2003), and depicted them as WebLogo (http://weblogo.threeplusone.com/create.cgi). (C) A comparison of the numerical values of the PTS1-predictions for those proteins is plotted for H. sapiens (x-axis) and D. rerio (y-axis) and depicted relative to the threshold for the evaluation of targeted proteins (>0, red) or the “twilight zone” (–10 < x < 0, grey); proteins with negative prediction are highlighted. (D) Systematic overview of orthologous fish proteins, which were either not found in D. rerio (ZADH2/PTGR3) or lack a PTS1 (Usp-L, long isoform; Prdx-5). (+) or (–) indicate presence or absence of the protein; 2x indicates 2 variants; traditional PTS1 identified (green) or not found (red); non-canonical PTS1 (yellow). (E) Schematic representation of the two isoforms of ubiquitin carboxyl-terminal hydrolase 2 (USP2) in H. sapiens (blue) and D. rerio (red). No PTS1 was found in the long isoform of Usp2 (Usp2-L). (F) Schematic representation of the two isoforms of peroxiredoxin-5 (Prdx-5) in H. sapiens (green) and D. rerio (orange). The long variant harbours an additional mitochondrial targeting signal, whereas the C-terminal sequence is identical. (G,H) Sequence comparison of the C-terminal end of USP2 orthologues (G) and PRDX5-orthologues (H). The loss of the PTS1 in Usp2-L is unique for D. rerio, whereas the PTS1 of human PRDX5 is found only in more ancient fish species.
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