Siderophore-Binding Periplasmatic Protein FhuD and Related Periplasmic Binding Proteins Involved in Bacterial Iron Uptake

Abstract To fulfill their nutritional requirement for iron, many microorganisms synthesize low‐molecular‐weight iron‐chelating compounds called siderophores . These iron sources are transported into the gram‐negative bacterial cell via specific uptake pathways that include an outer membrane receptor, a periplasmic binding protein (PBP), and an inner membrane ATP‐binding cassette (ABC) transporter. Gram‐positive bacteria lack an outer membrane, and thus the uptake of the ferric siderophore involves a membrane‐anchored PBP and an ABC transporter. Siderophores are classified as hydroxamate, catecholate, or hydroxycarboxylate type siderophores. This review details what is currently known about the PBP, FhuD (Fhu — ferric hydroxamate uptake), involved in the uptake of hydroxamate‐type siderophores. In addition, several structurally related periplasmic binding proteins that mediate bacterial metal ion transport are also discussed.