adenosine triphosphate binding cassete(ABC) transporter: The human adenosine triphosphate binding cassete (ABC) have seven subfamilies and 48 members. it is present in all the living organisms from human to microorganisms, ABC transporter can function as influx or efflux. ABC transporter is a membrane protein that have the ability to bind and hydrolyze the ATP and use it as a source of energy to efflux the substrate out of the cell, this transporter only require energy to efflux the substance out, in the influx procedure the substrate is passively transported to the cell with on need for energy. ABC transporters have an important role in regulating the absorption, distribution, metabolism and execration of cellular lipid and glucose, it controls the glucose and lipid metabolism by regulate the secretion and activation of insulin and lipase.
The structure of ABC transporter:the figure below shows the ABC transporter structure which consist of four domains, two of them are the binding site, it’s called trance membrane domains, the trance membrane domains are taking place in the cell membrane, and the other two are the ATP binding domains which are called nucleotide binding domains, they are taking place in the cytoplasm, the trance membrane domains binds to the substrate and the nucleotide biding domains binds to the ATP molecule. adenosine triphosphate ride binding cassette B1 (ABCB1):ATP binding cassette B1 (ABCB1) transporter comes from the ATP binding cassette subfamily B member one.it can be classified based on the structure of the polypeptide chain to full and half transporter, if the transporter is composed of one liked polypeptide chain it’s called full transporter, but if the transporter is present in tow separated polypeptide chain then it’s called half transporter.
The transporter uses the energy of ATP hydrolysis to establish a direct membrane movement which create a pocket like structure used to transport the substrate across the membrane. ABCB1 transporter in the abnormal condition is responsible for giving the cancer cells it’s multidrug resisting (MDR1) property, in this case the transporter can be named as permeability glycoprotein (p-gp). ABCB1 transporter is present in the brush porder membrane of the intestinal cells, biliary canalicular membrane of hepatocyte, luminal membrane of proxima, tubule epithelial cells of the kidney and endothelial cells of blood brain barrier. function of ABCB1:the main function of ATP binding cassette B1 (ABCB1) is to protect the cell by pumping the toxic component or metabolite out of the cell by decreasing there exposure to toxic molecules, as a result it limits the entry of the xenobiotic to the cell , it works in decreasing the drug bioavailability by excreting the drug from the body by the excretion organs like in the intestine epithelial cell where it pumps the drug to the intestinal lumen and in the liver where it pumps the drug to the bile duct, and protect the organs by decreasing the exposure of the cell to the toxic xenobiotic like in blood brain barrier, testes and placenta. This transporter Is characterized by its high transporter capacity and its various wide substrate recognition.
When ABCB1 transporter is over excerpted it causes multidrug resistance(MDR) which is responsible for making the resistance of drugs in the cancer cells. permeability glycoprotein (p-gp) is a glycoprotein encoded by the ABCB1 transporter it works in pumping the drugs to outside the cell which makes the drug concentration inside the cell much lower than the outside, as a result it protects the cancer cell from the anticancer drugs.