Metal import through microbial membranes.

Transport systems of Gram-negative bacteria coordinate the passage of metabolites through the outer membrane, periplasm, and the cytoplasmic membrane without compromising the protective properties of the cell envelope. Active transporters orchestrate the import of metals against concentration gradients. These thermodynamically unfavorable processes are coupled to both an electrochemical proton gradient and the hydrolysis of ATP. Crystallographic structures of transport proteins now define in molecular detail most components of an active metal import pathway from Escherichia coli.