In human, the ATP-binding cassette (ABC) family of transmembrane transporters has at least 48 genes and 7 gene subfamilies. This gene is a member of ABC gene subfamily A (ABCA). Genes within the ABCA family typically encode several thousand amino acids. Like other ABC transmembrane transporter proteins, this protein has 12 or more transmembrane alpha-helix domains that likely arrange to form a single central chamber with multiple substrate binding sites. It is also predicted to have two large extracellular domains and two nucleotide binding domains as is typical for ABCA proteins. Alternative splice variants have been described but their biological validity has not been demonstrated.[provided by RefSeq, Mar 2009].