Lysosomal targeting of the CLN7 membrane glycoprotein and transport via the plasma membrane require a dileucine motif

Traffic. 2010 Jul 1;11(7):987-1000. doi: 10.1111/j.1600-0854.2010.01073.x. Epub 2010 Apr 16.

Abstract

CLN7 is a polytopic lysosomal membrane protein deficient in variant late infantile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disorder. In this study fluorescence protease protection assays and mutational analyses revealed the N- and C-terminal tails of CLN7 in the cytosol and two N-glycosylation sites at N371 and N376. Both partially and non-glycosylated CLN7 were correctly transported to lysosomes. To identify lysosomal targeting motifs, we generated CD4-chimera fused to the N- and C-terminal domains of CLN7. Lysosomal localization of the chimeric proteins requires a consensus acidic dileucine-based motif in the N-terminus and two tandem tyrosine-based signals in the C-terminus. Mutation of these sorting motifs resulted in cell surface redistribution of CD4 chimeras. However, the dileucine-based motif is of critical importance for lysosomal localization of the full-length CLN7 in different cell lines. Cell surface biotinylation revealed that at equilibrium 22% of total CLN7 is localized at the plasma membrane. Mutation of the dileucine motif or the co-expression of dominant-negative mutant dynamin K44A led to a further increase of CLN7 at the plasma membrane. Our data demonstrate that CLN7 contains several cytoplasmic lysosomal targeting signals of which the N-terminal dileucine-based motif is required for the predominant lysosomal targeting along the indirect pathway and clathrin-mediated endocytosis of CLN7.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs* / genetics
  • Animals
  • Biological Transport / genetics
  • Biotinylation
  • COS Cells
  • Cell Line
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Chlorocebus aethiops
  • Clathrin / genetics
  • Clathrin / metabolism
  • Cytosol / metabolism
  • Endocytosis / genetics
  • Endocytosis / physiology
  • HeLa Cells
  • Humans
  • Leucine*
  • Lysosomal Membrane Proteins / genetics
  • Lysosomal Membrane Proteins / metabolism
  • Lysosomal Storage Diseases / genetics
  • Lysosomal Storage Diseases / metabolism
  • Lysosomes / genetics
  • Lysosomes / metabolism*
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Membrane Transport Proteins* / genetics
  • Membrane Transport Proteins* / metabolism
  • Protein Structure, Tertiary / genetics
  • Protein Transport / genetics
  • Recombinant Proteins / metabolism

Substances

  • Clathrin
  • Lysosomal Membrane Proteins
  • MFSD8 protein, human
  • Membrane Glycoproteins
  • Membrane Transport Proteins
  • Recombinant Proteins
  • Leucine