3.A.1.15.21
Mn²⁺ ABC uptake system, MntABC. Titratable transmembrane residues and a hydrophobic plug are essential for manganese import via the Bacillus anthracis ABC transporter MntBC-A (Kuznetsova et al. 2021). Zinc is a high-affinity inhibitor. The transmembrane metal permeation pathway is lined with six titratable residues that can coordinate the positively charged metal, and mutagenesis studies showed that they are essential for manganese transport. Modelling suggested that access to these titratable residues is blocked by a ladder of hydrophobic residues, and ATP-driven conformational changes open and close this hydrophobic seal to permit metal binding and release. The conservation of this arrangement of titratable and hydrophobic residues among ABC transporters of transition metals suggests a common mechanism (Kuznetsova et al. 2021).