Table I.
Structure and function of ABCA subfamily proteins.
| Proteins | Structure | Function | (Refs.) |
|---|---|---|---|
| ABCA1 | Length, 2,261 amino acids; contains two TMDs, and a polar cluster on one side of | Synthesis of HDL, exporting cholesterol out of the cells, lipid efflux activity. Mutation of the | |
| TMD1 close to the intracellular boundary. | ABCA1 gene may induce Tangier disease and familial hypoalphalipoproteinemia. Tumor suppressor function in cancer. | ||
| ABCA2 | Coding region 7.3 kb in size, codes for a 2,436-amino acid polypeptide, comprises 48 exons. | Highly expressed in brain tissue; may play a role in macrophage lipid metabolism and neural development. | (34) |
| ABCA3 | Consists of 33 exons encoding a 1,704-amino acid (~150 kDa) protein. | Mutation of the ABCA3 gene is the most common cause of surfactant deficiency and is associated with cataract-microcornea syndrome. | (35) |
| ABCA4 | Transcribes a large retina-specific protein with two TMDs, two glycosylated ECDs and two NBDs. | An inward-directed retinoid flippase; mutation of ABCA4 induces Stargardt's disease. | |
| ABCA5 | Consists of 1,642 amino acid residues, with two sets of six transmembrane segments and an NBD. | Mutations in ABCA5 cause hair overgrowth and may be associated with a lysosomal disease, particularly in cardiomyocytes and follicular cells. | (36) |
| ABCA7 | Spans a region of ~32 kb and comprises 46 exons. | Predisposes to Alzheimer's disease. | (37) |
| ABAC9 | Consists of 39 exons, genomic region of ~85 kb chromosome 17q24.2. | Involved in monocyte differentiation and macrophage lipid homeostasis. | (38) |
| ABCA10 | The coding sequence of ABCA10 is 4.6 kb in size and codes for a 1,543-amino acid protein. | Involved in macrophage lipid homeostasis. | |
| ABCA12 | Located on the long (q) arm of chromosome 2 between positions 34 and 35. | Active in some types of skin cells, linked to harlequin-type ichthyosis. | |
| ABCA13 | Coding region is 6.7 kb in size and encodes a protein consisting of 2,143 amino acids with a predicted molecular weight of 240 kDa. | Linked to psychiatric disorders such as schizophrenia, bipolar disorder and depression. | (39) |
ABC, ATP-binding cassette; TMD, transmembrane domain; HDL, high-density lipoprotein; ECD, extracellular domain; NBD, nucleotide-binding domain.