|Home | About | Journals | Submit | Contact Us | Français|
♦ See referenced article, J. Biol. Chem. 2013, 288, 21228–21235
ATP-binding cassette (ABC) transporters, categorized either as exporters or importers, are one of the largest groups of transmembrane proteins. Importers, which can be further subcategorized, are critical in bacteria for the uptake of cofactors and nutrients. Type I importers have been well studied, but less is known about the type II subcategory. In this Paper of the Week, a team led by Heather W. Pinkett at Northwestern University in Illinois studied the type II importer MolB2C2-A from Haemophilus influenza, which takes up the cofactor molybdate. The investigators compared MolB2C2-A with the better known type II importer for the larger vitamin B12 molecule, BtuC2D2. The investigators analyzed MolB2C2-A by disulfide cross-linking and EPR spectroscopy. They established that unlike in BtuC2D2, nucleotide binding in MolB2C2-A was coupled to a small conformational change at the periplasmic gate. This change, the authors say, “is akin to unlocking a swinging door: allowing just enough space for molybdate to slip into the cell.” On the cytoplasmic side, one MolB2C2-A gate remained open while another gate closed in the presence of ATP. The authors concluded that MolB2C2-A was similar to BtuC2D2 in using a peristaltic pumping mechanism but with differences at two of the three gates.