Picture from Miedel MT et al. (2012) PLoS One "A pro-cathepsin L mutant is a luminal substrate for ...."

Figure 1. Mutations in the prepro-domain of CPL (CPL-1W32A;Y35A) cause ER accumulation and prevent trafficking to the lysosome.(A) Alignment of the primary amino acid sequence from C. elegans (Cel) CPL-1[NP_507199.1] with human (Hsa) cathepsins K [AAH16058.1] (CATK), L[NP_666023.1] (CATL), S [AAC37592.1] (CATS) and V [BAA25909.1] (CATV) using the ClustalW algorithm. Blue shading indicates the three tryptophanresidues within the human CATL-like prepro-domain that are critical for proper folding [14]. Arrowheads indicate the residues mutated to alanines inthe CPL-1 sequence to generate CPL-1W32A;Y35A::YFP. [ ] denote accession numbers of individual amino acid sequences used in alignments. (B)Schematic representation of the expression constructs used to express either wild-type or mutant CPL-1::YFP. The asterisks denote location of themutated resides within the prepro-domain (green line). The intron locations were not depicted. (C-J) Transgenic animals expressing CPL-1::YFP (C-F)or CPL-1W32A;Y35A::YFP (G-J) were examined by confocal microscopy and maximum intensity projections are displayed. Both lines were also coinjectedwith a DsRed::KDEL transgene to mark the ER (D, H), and were also incubated with BSA::AlexaFluor647 to label the endo-lysosomalcompartment (E, I). CPL-1::YFP showed a punctate distribution within intestinal cells (C) that co-localized with BSA::AlexaFluor647 (E, F), but did notoverlap with DsRed::KDEL (D). This pattern suggested CPL-1::YFP was trafficking correctly to the endolysosomal compartment. In contrast, CPL-1W32A;Y35A::YFP displayed a fine reticular pattern (G, inset) with a few intracellular inclusions (G, arrowheads) that co-localized with the DsRed::KDEL ERmarker (H and J), but not the BSA::AlexaFluor647 endo-lysosomal marker (I). Insets of single z plane images are included to highlight the distinctreticular fluorescence pattern displayed by the DsRed::KDEL ER marker and the YFP fluorescence pattern observed in animals expressing CPL-1W32A;Y35A::YFP. Scale bar represents 10 um.