3.A.1.15.14
High affinity Mn²⁺ uptake complex, PsaABC (Lisher et al. 2013). The crystal structure of the manganese transporter PsaBC from Streptococcus pneumoniae has been solved in an open-inward conformation (Neville et al. 2021). The type II transporter has a tightly closed transmembrane channel due to "extracellular gating" residues that prevent water permeation and ion reflux. Below these residues, the channel contains a metal coordination site, which is essential for manganese translocation. Mutagenesis of the extracellular gate perturbs manganese uptake, while coordination site mutagenesis abolishes import. These structural features are well conserved in metal-specific ABC transporters and are represented throughout the kingdoms of life. Collectively, these results define the structure of PsaBC and reveal the features required for divalent cation transport (Neville et al. 2021).