Related Experiment Videos
TonB-dependent outer membrane transport: going for Baroque?
1Department of Molecular Physiology and Biological Physics, University of Virginia, PO Box 800736, Charlottesville, VA 22908-0736, USA. mwiener@virginia.edu
Current Opinion in Structural Biology
|July 26, 2005
Summary
TonB-dependent outer membrane transporters (TBDTs) import vital micronutrients into Gram-negative bacteria. Current structures reveal transporter architecture but not the mechanism of substrate passage, posing a key challenge.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Gram-negative bacteria import essential organometallic micronutrients via TonB-dependent outer membrane transporters (TBDTs).
- TBDTs utilize the TonB protein, a component of an inner membrane complex, to facilitate transport.
- Existing structural data reveals TBDT architecture in substrate-free and bound states, featuring an N-terminal domain occluding a beta barrel.
Purpose of the Study:
- To elucidate the molecular mechanism of substrate transport through TBDTs.
- To reconcile structural data with functional and in vivo experimental findings.
- To address the "hatch-barrel problem" concerning substrate translocation.
Main Methods:
- Analysis of five crystal structures of TBDTs.
- Examination of solution NMR and X-ray crystallographic structures of TonB domains.
- Integration of thermodynamic, biochemical, and bacteriological studies.
Main Results:
- Crystal structures clearly depict TBDT architecture in energy-independent states.
- TonB domains exhibit significant structural plasticity.
- Current structures do not capture the energy-dependent, in vivo conformations crucial for transport.
Conclusions:
- The precise mechanism of substrate translocation through TBDTs remains elusive.
- Reconciling diverse experimental data is essential for understanding the transport cycle.
- Further research is needed to experimentally determine the detailed molecular mechanism of TBDT-mediated transport.