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Dynamics and function in a bacterial ABC transporter: simulation studies of the BtuCDF system and its components
Anthony Ivetac1, Jeff D Campbell, Mark S P Sansom
1Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
Biochemistry
|February 17, 2007
Summary
Adenosine triphosphate (ATP) binding drives conformational changes in the BtuCD transporter, facilitating vitamin B12 uptake in bacteria. BtuF binding induces asymmetric changes, suggesting a mechanism for solute transport.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- ATP-binding cassette (ABC) transporters utilize ATP hydrolysis to move solutes across membranes.
- BtuCD is an ABC transporter in Gram-negative bacteria responsible for vitamin B12 import.
- BtuF periplasmic protein binds vitamin B12 and delivers it to the BtuCD transporter.
Purpose of the Study:
- To investigate the conformational dynamics of the BtuCD transporter complex.
- To elucidate the role of ATP binding and BtuF interaction in BtuCD transport mechanism.
- To explore the mechanism of vitamin B12 transport by BtuCDF.
Main Methods:
- Molecular dynamics simulations of BtuCD and BtuCDF complexes.
- Simulations of isolated BtuD and BtuF proteins.
- Analysis of conformational changes with and without bound ATP.
Main Results:
- ATP binding induces symmetrical closure of nucleotide-binding domains (NBDs) in BtuD, but not in BtuCD.
- BtuF binding to BtuCD leads to asymmetric NBD closure, consistent with alternating hydrolysis.
- Principal components analysis revealed motions in BtuCD aligning with existing transport models.
Conclusions:
- ATP binding and BtuF interaction are critical for BtuCD transporter conformational changes.
- The observed asymmetry in ATP-binding sites suggests a step in the alternating hydrolysis mechanism.
- Simulation data provides insights into the molecular mechanism of vitamin B12 transport.
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