TonB-dependent transporters: regulation, structure, and function.

Title	TonB-dependent transporters: regulation, structure, and function.
Authors	Nicholas Noinaj, Maude Guillier, Travis J Barnard, Susan K Buchanan
Magazine	Annual review of microbiology
Date	01/01/2010
DOI	10.1146/annurev.micro.112408.134247
Introduction	TonB-dependent transporters (TBDTs) are key bacterial outer membrane proteins that facilitate the transport of ferric chelates, siderophores, vitamin B12, nickel complexes, and carbohydrates. This energy-intensive process uses the proton motive force and a complex of three inner membrane proteins, TonB-ExbB-ExbD, to transfer energy to the outer membrane. The substrates for siderophores vary from simple small molecules such as citrate to large proteins such as serum transferrin and haemoglobin. Due to the essential role of iron uptake in bacterial survival, TBDTs expression is tightly regulated through metal-dependent regulators, σ/anti-σ factor systems, small RNAs, and even riboswitches. Recent structural advances have enhanced understanding of siderophore selectivity, binding, outer membrane signal transduction, and interaction with the TonB-ExbB-ExbD complex. Yet, the transport mechanism remains unclear. This review highlights recent developments in the regulation, structure, and function of TBDTs while addressing unresolved questions.
Quote	Nicholas Noinaj, Maude Guillier and Travis J Barnard et al. TonB-dependent transporters: regulation, structure, and function.. Annual review of microbiology. 2010. Vol. 64. DOI: 10.1146/annurev.micro.112408.134247
Topics	Biomedical Materials