Multidrug Resistance Protein, Na+ Transporting Mrp (Mrp) Superfamily

Mrp of Bacillus subtilis is a 7 subunit Na+/H+ antiporter complex (2.A.63.1.4). All subunits are homologous to the subunits in other members of this monovalent cation (K+ or Na+): proton antiporter-3 (CPA3) family as well as subunits in the archaeal hydrogenases (3.D.1.4.1 and 3.D.1.4.2) which share many subunits with NADH dehydrogenase subunits (3.D.1). The largest subunit of the Mrp complex (Mrp A and Mrp D) are homologous to the subunits in NADH dehydrogenases (NDH, ND2, ND4 and ND5 in the fungal NADH dehydrogenase complex) and most other NDHs. (TC#3.D.1) as well are subunits in the F420H2 dehydrogenase of Methanosarcina mazei (TC#3.D.9.1.1). (Zickermann et al. 2015). New subunits in three TC families are homologous, and in all such systems, these subunits may function as Na+/K+ and/or H+ transporters.