ATP-binding cassette domain of the lipid transporters, subfamily A
The ABCA subfamily mediates the transport of a variety of lipid compounds. Mutations of members of ABCA subfamily are associated with human genetic diseases, such as, familial high-density lipoprotein (HDL) deficiency, neonatal surfactant deficiency, degenerative retinopathies, and congenital keratinization disorders. The ABCA1 protein is involved in disorders of cholesterol transport and high-density lipoprotein (HDL) biosynthesis. The ABCA4 (ABCR) protein transports vitamin A derivatives in the outer segments of photoreceptor cells, and therefore, performs a crucial step in the visual cycle. The ABCA genes are not present in yeast. However, evolutionary studies of ABCA genes indicate that they arose as transporters that subsequently duplicated and that certain sets of ABCA genes were lost in different eukaryotic lineages.
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