A dileucine signal situated in the C-terminal tail of the lysosomal membrane protein p40 is responsible for its targeting to lysosomes

Marielle Boonen , Roberta Rezende de Castro , Gaëlle Cuvelier , Isabelle Hamer , Michel Jadot (1)

1 Department of Physiological Chemistry

Transport of newly synthesised lysosomal membrane proteins from the TGN to the lysosomes is due to the presence of specific signals in their cytoplasmic domains that are recognised by cytosolic adaptors. p40, a hypothetical transporter of 372 amino acids localised in the lysosomal membrane, contains four putative lysosomal sorting motifs in its sequence: three of the YXXΦ–type (Y6QLF, Y106VAL, Y333NGL) and one of the [D/E]XXXL[L/I]-type (EQERL360L361). To test the implication of these motifs in the biosynthetic transport of p40, we replaced the most critical residues of these consensus sequences, the tyrosine or the leucine-leucine pair, by alanine or alanine-valine, respectively. We analysed the subcellular localisation of the mutated p40 proteins in transfected HeLa cells by confocal microscopy and by biochemical approaches (subcellular fractionation on self-forming Percoll density gradients and cell surface biotinylation). Our results show that p40 is mis-targeted to the plasma membrane when its dileucine motif is disrupted. No role of the tyrosine motifs could be put forward. Taken together, our results provide evidence that the sorting of p40 from the TGN to the lysosomes is directed by the dileucine EQERL360L361 motif situated in its C-terminal tail.

Mots clés: Life Sciences

Marielle Boonen, Roberta Rezende de Castro, Gaëlle Cuvelier, Isabelle Hamer, Michel Jadot. A dileucine signal situated in the C-terminal tail of the lysosomal membrane protein p40 is responsible for its targeting to lysosomes. Biochemical Journal, 2008, 414 (3), pp.431-440. ⟨10.1042/BJ20071626⟩. ⟨hal-00478932⟩