Functional dissection of transmembrane domains of human TAP-like (ABCB9)

An ABC transporter, TAP-Like (TAPL), was dissected into its amino-terminal transmembrane domain and the following core domain. When these domains were transiently expressed as tagged proteins with a His6- or Myc-epitope tag, the amino-terminal ones (Met¹-Lys¹⁸²) could not associate with each other, or with the full-length transporter (Met¹-Ala⁷⁶⁶). However, both the core domain (Arg¹⁴¹-Ala⁷⁶⁶) and full-length protein mutually interacted. The amino-terminal domain (Met¹-Arg¹⁴¹) as well as the full-length transporter fused with fluorescent protein GFP was sorted to lysosomal membranes upon their stable expression, as visualized by means of fluorescent microscopy, while the core domain (Arg¹⁴¹-Ala⁷⁶⁶) was broadly distributed in the intra-cellular membranes. These results suggest that the sorting signal for lysosomes is present within the amino-terminal transmembrane domain (Met¹-Arg¹⁴¹) of the TAPL molecule.