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Function
Efflux pumps function to move different substances out of cells such as ions, lipids, and molecules that are toxic for the cell. ATP-binding cassette (ABC) transporters are a common class of efflux pumps found in all forms of life. Humans have forty-eight known ABC transporters.
An ATP-switch model for transport has been used to describe ABC transporters. For transport, a switch between two conformations of the nucleotide binding domain dimer serves as the promoter. The binding of ATP induces the rotation of domains within the nucleotide-binding domain. A closed dimer with two molecules of ATP between the dimer is formed. The hydrolysis of ATP into ADP and Pi returns the dimer to an open configuration. The binding of ATP to the nucleotide binding domains and the closed dimer formation induces conformational changes in the transmembrane domains that aid in the movement of substrate out of the cell. The transmembrane domain is shifted so that the domain is visible to the extracellular face of the membrane and the substrates can then be released. Similar to the nucleotide-binding domain, the hydrolysis of ATP to ADP and Pi restores the dimer to its beginning conformation.
Structural Highlights
This is an image of mitochondrial ABC transporter ABCB6
Energetics
