Kobayashi Ayako, Maeda Tatsuo, Maeda Masatomo
Laboratory of Biochemistry and Molecular Biology, Graduate School of Pharmaceutical Sciences, Osaka University, Japan.
Biol Pharm Bull. 2004 Dec;27(12):1916-22. doi: 10.1248/bpb.27.1916.
Transporter associated with antigen processing (TAP)-like (TAPL, ABCB9) is a half-type ATP binding cassette (ABC) protein belonging to subfamily B highly homologous to the TAP, a hetero-dimeric complex consisting of a TAP1 and a TAP2 subunit. Human TAPL, to which was tagged with green fluorescence protein (GFP) at its carboxyl terminus (TAPL-GFP), showed fluorescence on intracellular membranes similar to TAP1-GFP. A truncated form of TAPL-L-GFP (M1-S275 was followed by GFP) showed a similar cellular fluorescence pattern to TAPL-GFP. However, the fluorescence of TAPL-S-GFP (M1-G75) was distributed over all the cellular membranes including plasma membrane, indicating that the amino terminal region of TAPL (M1-S275) is essential for its localization to the intracellular membranes. A co-expression study demonstrated that TAPL-S-GFP was co-localized with TAPL-DR (DsRed-tagged TAPL) or TAP1-DR, suggesting that TAPL is able to interact with not only itself but also with TAP1 through the M1-G75 region of TAPL. It is also proposed that a further downstream sequence of TAPL would confine the distribution of TAPL-S-GFP to the intracellular membranes. Similarly, the distribution of TAP2-S-GFP (M1-R88) was restricted to the intracellular membranes by TAPL-DR or TAP1-DR, indicating that the M1-R88 region of TAP2 is able to interact with TAPL as well as TAP1. Therefore, TAPL would form a homo-dimer with itself, and a hetero-dimer with TAP1 and TAP2. TAPL-GFP was co-localized with the fluorescence endoplasmic reticulum (ER) marker, suggesting that TAPL is mainly localized to the ER in the intracellular membranes.
抗原加工相关转运体（TAP）样蛋白（TAPL，ABCB9）是一种半型ATP结合盒（ABC）蛋白，属于与TAP高度同源的B亚家族，TAP是一种由TAP1和TAP2亚基组成的异二聚体复合物。人TAPL在其羧基末端标记有绿色荧光蛋白（GFP）（TAPL-GFP），在细胞内膜上显示出与TAP1-GFP相似的荧光。TAPL-L-GFP的截短形式（M1-S275后接GFP）显示出与TAPL-GFP相似的细胞荧光模式。然而，TAPL-S-GFP（M1-G75）的荧光分布在包括质膜在内的所有细胞膜上，表明TAPL的氨基末端区域（M1-S275）对于其定位于细胞内膜至关重要。一项共表达研究表明，TAPL-S-GFP与TAPL-DR（DsRed标记的TAPL）或TAP1-DR共定位，表明TAPL不仅能够通过TAPL的M1-G75区域与自身相互作用，还能与TAP1相互作用。还提出TAPL的进一步下游序列将限制TAPL-S-GFP在细胞内膜上的分布。同样，TAP2-S-GFP（M1-R88）的分布通过TAPL-DR或TAP1-DR限制在细胞内膜上，表明TAP2的M1-R88区域能够与TAPL以及TAP1相互作用。因此，TAPL将与自身形成同二聚体，并与TAP1和TAP2形成异二聚体。TAPL-GFP与内质网（ER）荧光标记物共定位，表明TAPL主要定位于细胞内膜中的内质网。
