THE RESIDUES LEU(ILE)(475)-ILE(LEU,VAL,ALA)(476), CONTAINED IN THE EXTENDED CARBOXYL CYTOPLASMIC TAIL, ARE CRITICAL FOR TARGETING OF THE RESIDENT LYSOSOMAL MEMBRANE-PROTEIN LIMP-II TO LYSOSOMES

LIMP II, a type II lysosomal integral membrane protein, and the CD36/L IMP II construct are targeted to lysosomes by means of a signal expres sed in the tyrosine-lacking carboxyl cytoplasmic tail of LIMP II (Vega , M. A., Rodriguez, F., Segui, B., Cales, C., Alcalde, J., and Sandova l, I. V. (1991) J. Biol. Chem. 266, 16269-16272; Vega, M. A., Segui-Re al, B., Garcia, J. A., Cales, C., Rodriguez, F., Vandekerckhove, J., a nd Sandoval, I. V. (1991) J. Biol. Chem. 266, 16818-16824). Substituti on of Leu(475) with Ile resulted in a decreased efficiency of targetin g. Mutant forms produced by substituting Leu(475) by hydrophobic resid ues with either large (Val) or small (Ala, Gly) side chains, or by a c harged residue (Asp), showed inhibited targeting. In contrast, the con tiguous Ile(476) residue could be replaced by either Leu, without loss in the efficiency of targeting, or by Val or Ala, with some impedimen t. Substitution of Ile(476) by either Gly or Asp inhibited completely the targeting. The addition of the sequence Ser-Trp-Asp to the carboxy l end of the construct did not interfere with targeting. Data from H-1 NMR analysis of the icosapeptide corresponding to the carboxyl cytopl asmic tail of LIMP II indicated the predominance of structures with ex tended random coil conformations, suggesting that the targeting signal is contained in a domain with an extended configuration.