ATP-BINDING CASSETTE TRANSPORTERS (ABC). NOMENCLATURE, STRUCTURE, MOLECULAR DIVERSITY, FUNCTION, CONTRIBUTION TO THE FUNCTIONING OF THE XENOBIOTICS TRANSFORMATION SYSTEM (А REWIEW)

ATP-binding cassette (ABC) transporters are membrane proteins responsible for removing various substrates from cells through cell membranes using the energy derived from ATP hydrolysis. The human genome codes for 48 ABC transporters, which are categorized into eight families: ABCA, ABCB, ABCC, ABCD, ABCE, ABCF, ABCG, ABCH. An ABC molecule consists of two nucleotide-binding domains (NBD) and two transmembrane domains (TMD) which transport substrates (NBD–TMD–NBD–TMD), or exists as a half-transporter consisting of one NBD and one TMD, which functions as a dimer. It is assumed that the ABC transport cycle is a four-stage one. The energy obtained in the hydrolysis of ATP is utilized to remove the substrate from the complex with the transporter molecule and restore it in its original state. In mammals, ABC were, apart from cancer cells, found in many tissues, such as the brain, adrenal glands, kidneys, lungs, testes, liver, placenta, intestines. ABC substrates encompass a wide range of compounds of both endo- and exogenous origin. Some ABC are involved in metabolizing xenobiotics, actively removing both lipophilic compounds that pass through the plasma membrane, and hydrophilic metabolites and conjugates formed in biotransformation phases I and II. A number of studies have demonstrated the interaction between the CYP3A4 enzyme from the P450 cytochrome group (biotransformation phase I) and the transporter АВСВ1. The ABCG2 transporter from the liver and intestines was found to actively export metabolites of biotransformation phase II.