EPR spectroscopy of MolB2C2-a reveals mechanism of transport for a bacterial type II molybdate importer. J Biol Chem 2013 Jul 19;288(29):21228-21235
Date
05/28/2013Pubmed ID
23709218Pubmed Central ID
PMC3774390DOI
10.1074/jbc.M113.483495Scopus ID
2-s2.0-84880536145 (requires institutional sign-in at Scopus site) 19 CitationsAbstract
In bacteria, ATP-binding cassette (ABC) transporters are vital for the uptake of nutrients and cofactors. Based on differences in structure and activity, ABC importers are divided into two types. Type I transporters have been well studied and employ a tightly regulated alternating access mechanism. Less is known about Type II importers, but much of what we do know has been observed in studies of the vitamin B12 importer BtuC2D2. MolB2C2 (formally known as HI1470/71) is also a Type II importer, but its substrate, molybdate, is ∼10-fold smaller than vitamin B12. To understand mechanistic differences among Type II importers, we focused our studies on MolBC, for which alternative conformations may be required to transport its relatively small substrate. To investigate the mechanism of MolBC, we employed disulfide cross-linking and EPR spectroscopy. From these studies, we found that nucleotide binding is coupled to a conformational shift at the periplasmic gate. Unlike the larger conformational changes in BtuCD-F, this shift in MolBC-A is akin to unlocking a swinging door: allowing just enough space for molybdate to slip into the cell. The lower cytoplasmic gate, identified in BtuCD-F as "gate I," remains open throughout the MolBC-A mechanism, and cytoplasmic gate II closes in the presence of nucleotide. Combining our results, we propose a peristaltic mechanism for MolBC-A, which gives new insight in the transport of small substrates by a Type II importer.
Author List
Rice AJ, Alvarez FJD, Schultz KM, Klug CS, Davidson AL, Pinkett HWAuthors
Candice S. Klug PhD Professor in the Biophysics department at Medical College of WisconsinKathryn M. Schultz Research Scientist I in the Biophysics department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
Adenosine TriphosphateBacterial Proteins
Biological Transport
Cross-Linking Reagents
Cytoplasm
Disulfides
Electron Spin Resonance Spectroscopy
Haemophilus influenzae
Ligands
Membrane Transport Proteins
Models, Biological
Molybdenum
Periplasm
Protein Structure, Secondary