Transport of nickel and cobalt ions into bacterial cells by S components of ECF transporters.
Energy-coupling factor (ECF) transporters form a distinct group of ABC-type micronutrient importers in prokaryotes that do not contain extracytoplasmic, soluble substrate-binding proteins. Instead, they consist of a transmembrane substrate-specific S component that interacts with a module composed of a moderately conserved transmembrane (T) component and ABC ATPases. The majority of S components is considered to act as high-affinity binding proteins that strictly depend on their cognate T and ATPase units for transport activity. For a fraction of biotin-specific S units, however, transport activity was demonstrated in their solitary state. Here, we compared the activities of nickel- and cobalt-specific ECF transporters in the presence and absence of their T and ATPase units. Accumulation assays with radioactive metal ions showed that the truncated transporters led to approx. 25% of cell-bound radioactivity compared to the holotransporters. Activity of urease, an intracellular nickel-dependent enzyme, was used as a reporter and clearly indicated that the cell-bound radioactivity correlates with the cytoplasmic metal concentration. The results demonstrate that S units of metal transporters not only bind their substrates on the cell surface but mediate transport across the membrane, a finding of general importance on the way to understand the mechanism of ECF transporters.
Humboldt-Universität zu Berlin, Institut für Biologie/Mikrobiologie, Chausseestraße 117, 10115, Berlin, Germany.
Franziska
F
Kirsch
Thomas
T
Eitinger
D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D001426:Bacterial Proteins / Q000502:physiology*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D003035:Cobalt / Q000378:metabolism*; D021902:Enterobacter aerogenes / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D009532:Nickel / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000235:genetics; D014510:Urease / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D003035:Cobalt; D009532:Nickel; D014510:Urease