Six-transmembrane helical domain 2 (TMD2) of multidrug resistance-associated protein 4 (MRP4) and similar proteins
This group represents the six-transmembrane domain 2 (TMD2) of multidrug resistance-associated protein 4 (MRP4), which belongs to the subfamily C of the ATP-binding cassette (ABC) transporter superfamily. The MRP subfamily (ABCC subfamily) is composed of 13 members, of which MRP1 to MRP9 are the major transporters that cause multidrug resistance in tumor cells by pumping anticancer drugs out of the cell. These nine MRP members function as ATP-dependent exporters for endogenous substances and xenobiotics. MRP family can be divided into two groups, depending on their structural architecture. MRP4, MRP5, MRP8, and MRP9 (ABCC4, 5, 11 and 12, respectively) have a typical ABC transporter structure and each composed of two transmembrane domains (TMD1 and TMD2) and two nucleotide domains (NBD1 and NBD2). On the other hand, MRP1, 2, 3, 6 and 7 (ABCC1, 2, 3, 6 and 7, respectively) have an additional N-terminal five transmembrane segments in a single domain (TMD0) connected to the core (TMD-NBD) by a cytoplasmic linker (L0).
Comment:All members of this ABC transporter family contain 6 alpha-helices in each transmembrane domain (TMD) for a total of 12 TM segments in the complete transporter.
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