The structural basis of bacterial manganese import

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Metal ions are vital for life, with ATP-binding cassette (ABC) permeases mediating micronutrient uptake in prokaryotes.
• The structural basis for metal ion transport via ABC permeases, particularly for transition metals like manganese, remains largely unknown.

Purpose of the Study:

• To elucidate the structural characteristics of the manganese transporter PsaBC from *Streptococcus pneumoniae*.
• To identify key structural features responsible for manganese translocation across the cell membrane.

Main Methods:

• X-ray crystallography to determine the structure of PsaBC.
• Site-directed mutagenesis to investigate the functional roles of identified structural elements.

Main Results:

• The crystal structure of PsaBC was determined in an open-inward conformation, revealing a closed transmembrane channel with "extracellular gating" residues.
• A novel metal coordination site, crucial for manganese translocation, was identified below the extracellular gate.
• Mutagenesis of the extracellular gate affected manganese uptake, while mutations in the coordination site abolished import.

Conclusions:

• The study defines the structure of the PsaBC manganese transporter.
• Key structural features, including the extracellular gate and a novel coordination site, are essential for divalent cation transport.
• These findings have implications for understanding metal transport across life kingdoms.