Characterization of CD36/LIMPII homologues in Dictyostelium discoideum.

The CD36/LIMPII family is ubiquitously expressed in higher eukaryotes and consists of integral membrane proteins that have in part been characterized as cell adhesion receptors, scavenger receptors, or fatty acid transporters. However, no physiological role has been defined so far for the members of this family that localize specifically to vesicular compartments rather than to the cell surface, namely lysosomal integral membrane protein type II (LIMPII) from mammals and LmpA from the amoeba Dictyostelium discoideum. LmpA, the first described CD36/LIMPII homologue from lower eukaryotes, has initially been identified as a suppressor of the profilin-minus phenotype. We report the discovery and initial characterization of two new CD36/LIMPII-related proteins, both of which share several features with LmpA: (i) their size is considerably larger than that of the CD36/LIMPII proteins from higher eukaryotes; (ii) they show the characteristic "hairpin" topology of this protein family; (iii) they are heavily N-glycosylated; and (iv) they localize to vesicular structures of putative endolysosomal origin. However, they show intriguing differences in their developmental regulation and exhibit different sorting signals of the di-leucine or tyrosine-type in their carboxyl-terminal tail domains. These features make them promising candidates as a paradigm for the study of the function and evolution of the as yet poorly understood CD36/LIMPII proteins.