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. 2007 Aug 31;3(8):e115. doi: 10.1371/journal.ppat.0030115

Figure 1. TgSOD2 Contains an Unusual Bipartite N-Terminal Signal and Is Targeted to both Mitochondrion and Apicoplast.

Figure 1

(A) Alignment of the N-termini of SOD sequences from apicomplexan parasites and two bacteria. Putative SPs as predicted by SignalP are underlined in black, and putative mitochondrial transit peptides as predicted by TargetP and MitoProt are underlined in red. The arrowhead denotes the arginine residue mutated in another study [16]. The numbers in black circles above the PfSOD2 sequence denote the two first methionines.

(B) Bimodal targeting of TgSOD2. Incomplete colocalization of SOD2myc with the two mitochondrial markers PRX3Ty and SOD3Ty shows that SOD2 is targeted to both the mitochondrion and an additional compartment (panels A and B). Colocalization of SOD2myc (in green) with the apicoplast marker SPTP(ACP)-DsRed demonstrates that SOD2 is also targeted to the apicoplast (panel C). Scale bars represent 2 μm.

(C) Immunoelectron microscopy on parasites stably expressing tagged proteins reveals SOD2Ty to be present in both the mitochondrion and the apicoplast of T. gondii (panels A and B), whereas SOD3Ty exclusively localizes to the parasite mitochondrion (panels C and D). Panels C and D depict two serial sections of the same cell (one section in between not shown). Ap, apicoplast; Go, Golgi apparatus; Mi, mitochondrion; Nu, nucleus. The arrowheads indicate the multiple membranes surrounding the apicoplast. Scale bars represent 200 nm.