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

Abstract

LIMP II, a type II lysosomal integral membrane protein, and the CD36/LIMP II construct are targeted to lysosomes by means of a signal expressed in the tyrosine-lacking carboxyl cytoplasmic tail of LIMP II (Vega, M. A., Rodríguez, F., Segui, B., Cales, C., Alcalde, J., and Sandoval, I. V. (1991) J. Biol. Chem. 266, 16269-16272

Vega, M. A., Segui-Real, B., García, J. A., Cales, C., Rodríguez, F., Vandekerckhove, J., and Sandoval, I. V. (1991) J. Biol. Chem. 266, 16818-16824). Substitution of Leu(475) with Ile resulted in a decreased efficiency of targeting. Mutant forms produced by substituting Leu(475) by hydrophobic residues with either large (Val) or small (Ala, Gly) side chains, or by a charged residue (Asp), showed inhibited targeting. In contrast, the contiguous Ile(476) residue could be replaced by either Leu, without loss in the efficiency of targeting, or by Val or Ala, with some impediment. Substitution of Ile(476) by either Gly or Asp inhibited completely the targeting. The addition of the sequence Ser-Trp-Asp to the carboxyl end of the construct did not interfere with targeting. Data from H-1 NMR analysis of the icosapeptide corresponding to the carboxyl cytoplasmic tail of LIMP II indicated the predominance of structures with extended random coil conformations, suggesting that the targeting signal is contained in a domain with an extended configuration.