ATP-binding cassette subfamily B member 9 (ABCB9, also known as TAP-like and TAPL) is a eukaryotic member of the ABC transporter family. It translocates peptides from the cytosol into the lumen of lysosomes []. It forms a homodimer and functions as a low affinity transporter that displays a broad peptide length specificity for 6-mer up to at least 59-mer peptides, with an optimum of 23-mers []. Positively charged, aromatic, or hydrophobic residues are more efficiently transported than negatively charged ones [].The ABC transporter family is a group of membrane proteins that use the hydrolysis of ATP to power the translocation of a wide variety of substrates across cellular membranes. ABC transporters minimally consist of two conserved regions: a highly conserved nucleotide-binding domain (NBD) and a less conserved transmembrane domain (TMD). Eukaryotic ABC proteins are usually organised either as full transporters (containing two NBDs and two TMDs), or as half transporters (containing one NBD and one TMD), that have to form homo- or heterodimers in order to constitute a functional protein [].
