Distinct reading of different structural determinants modulates the dileucine-mediated transport steps of the lysosomal membrane protein LIMPII and the insulin-sensitive glucose transporter GLUT4.
Leucine-based motifs mediate the sorting of membrane proteins at such cellular sites as the trans-Golgi network, endosomes, and plasma membrane. A Leu paired with a second Leu, Ile, or Met, while itself lacking the ability to mediate transport, is the key structural feature in these motifs. Here we have studied the structural differences between the leucine-based motifs contained in the COOH tails of LIMPII and GLUT4, two membrane proteins that are transported through the secretory pathway and are targeted to lysosomes () and to a perinuclear compartment adjacent to the Golgi complex (), respectively. LIMPII and GLUT4 display negatively (Asp(470)/Glu(471)) and positively (Arg(484)/Arg(485)) charged residues, respectively, at positions -4 and -5 upstream from the critical Leu residue. The change in the charge sign of residues -4 and -5 results in missorting of LIMPII and GLUT4. We note that the acidic Glu residue at position -4 is critical for efficient intracellular sorting of LIMPII to lysosomes, but is dispensable for its surface internalization by endocytosis. Efficient intracellular sorting and endocytosis of GLUT4 require an Arg pair between positions -4 and -7. These results are consistent with the existence of distinct leucine-based motifs and provide evidence of their different readings at different cellular sites.
Sandoval
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Centro de Biologia Molecular "Severo Ochoa," Consejo Superior de Investigaciones Cientificas, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, Madrid 28049, Spain. isandoval@cbm.uam.es
Martinez-Arca
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S
Valdueza
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J
Palacios
S
S
Holman
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GD
D016475:3T3 Cells; D000818:Animals; D018955:CD36 Antigens / Q000737:chemistry / Q000378:metabolism*; D019556:COS Cells; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D009124:Muscle Proteins; D021381:Protein Transport
D018955:CD36 Antigens; D051275:Glucose Transporter Type 4; D007328:Insulin; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C489452:Scarb2 protein, mouse; C495693:Slc2a4 protein, mouse; D007930:Leucine