CD36 is a ditopic glycoprotein with the N-terminal domain implicated in intracellular transport

The CD36 receptor sequence predicts two hydrophobic domains located at the N and C-termini of the protein, but there are conflicting reports as to whe ther the N-terminal uncleaved leader sequence functions as a transmembrane domain. To investigate the topology of CD36, we generated a panel of mutant s lacking either one or both hydrophobic regions and analyzed their folding and transport in COS-7 cells. The N- and the C-terminal hydrophobic region s were both sufficient to anchor CD36 in the membrane, and a FLAG epitope i nserted at the N-terminus was located intracellularly. These results indica te that CD36 adopts a ditopic configuration. Accordingly, neither N- nor C- terminal truncation mutants were secreted. Analysis with conformation-speci fic monoclonal antibodies showed that the N-terminal transmembrane domain t runcated molecule was slowly transported through the exocytic pathway and l argely accumulated intracellularly. Thus, dual membrane insertion dictates the correct topogenesis and seems to be necessary for efficient folding and intracellular transport. (C) 2000 Academic Press.