Figure 3. The N-Terminal Targeting Sequence of SOD2 Is Not Sufficient for Bimodal Targeting of Reporter Proteins.
(A) The predicted bipartite leader of SOD2 (SPTP) fused to reporter proteins (GFPmyc or DsRed) only localizes to the parasite mitochondrion as revealed by colocalization with the bimodally targeted SOD2 (SOD2Ty) (panels a and b), indicating that part of the information necessary for bimodal targeting of SOD2 resides in its mature protein portion. Replacement of the GFP or DsRed reporter by the predicted mature protein of SOD3 complements the bipartite leader of SOD2 (SPTP-SOD3Ty) and restores bimodal targeting to both organelles (panel c). The putative mitochondrial transit peptide of SOD3 in conjunction with the SOD2 mature protein leads to mitochondrial localization (panel d). The arrows indicate the apicoplast. Scale bars represent 2 μm.
(B) Western blot analysis of parasites stably expressing SOD2Ty, SOD3Ty, SPTP-SOD3Ty, and TP(SOD3)-SOD2Ty using anti-Ty-1 antibodies.
(C) Western blot analysis of parasite clones stably expressing SOD2myc and SPTP(SOD2)-GFPmyc using anti-myc and anti-actin antibodies, showing that the bimodal targeting of SOD2myc is not due to a difference in the expression level compared with the mitochondrion-targeted SPTP-GFPmyc.