High impact information on ABCB9

• Selective and ATP-dependent translocation of peptides by the homodimeric ATP binding cassette transporter TAP-like (ABCB9) [1].
• Although related to TAP, TAPL is unique as far as its interaction partners, transport properties, and substrate specificities are concerned, thus excluding that TAPL is part of the peptide-loading complex in the classic route of antigen processing via major histocompatibility complex class I molecules [1].
• These findings pave the way for further investigation into the potential novel function of ABCB9 in lysosomes [2].
• Northern analysis shows that the ABCB9 mRNA is expressed at a high level in testes and moderate levels in brain and spinal cord [2].
• ABCB9 protein appears to be most highly expressed in the Sertoli cells of the seminiferous tubules in mouse and rat testes [2].

Biological context of ABCB9

• The homodimeric ABCB9 (TAP-like) complex located in lysosomal compartments shares structural and functional similarities to TAP; however, its biological role seems to be different from the MHC I antigen processing [3].
• Examination of drug resistance activity of human TAP-like (ABCB9) expressed in yeast [4].
• The novel splicing variants of TAPL termed 12B and 12C have shorter carboxyl terminal amino acid sequences than 12A, reportedly a conserved isoform in rodents and human [5].
• The proximal promoter region of the TAPL gene lacks a canonical TATA-box but contains several GC-box elements [5].
• The TAPL gene consists of 12 exons including the first non-coding exon on human chromosome 12q23.34 [5].

Anatomical context of ABCB9

• The transporter associated with antigen processing (TAP)-like (TAPL, ABCB9) belongs to the ATP-binding cassette transporter family, which translocates a vast variety of solutes across membranes [1].
• It is also proposed that a further downstream sequence of TAPL would confine the distribution of TAPL-S-GFP to the intracellular membranes [6].
• 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 [6].
• Golden hamster spermatozoa were capacitated in vitro in TAPL 10K, and the maximum possible percentage of acrosome reaction was determined at 82.79% + 1.69% SD (P = 0.27; r = 0.21) [7].

Associations of ABCB9 with chemical compounds

• A mutation in Walker A motif, which lost ATP-binding activity of hTAPL, eliminated the enhanced sensitivity to valinomycin [4].
• A half-type ABC transporter, human TAP-like (hTAPL) tagged with histidine cluster, was expressed in budding yeast protease-deficient strain BJ5457, and the effect of expression for resistance to peptide compounds including antibiotics and proteinase inhibitor was examined [4].

Other interactions of ABCB9

• The lamprey protein also contains sequence stretches that resemble the putative peptide interacting parts of the TAP1 and TAP2 molecules, but are peppered with ABCB9-specific residues [8].
• TAPL forms a homodimer which is localized in lysosomes with a minor fraction in the ER [9].

References