Mapping Daunorubicin-binding Sites in the ATP-binding Cassette Transporter MsbA Using Site-specific Quenching by Spin Labels*S⃞
AUTOR(ES)
Smriti
FONTE
American Society for Biochemistry and Molecular Biology
RESUMO
ATP-binding cassette (ABC) transporters transduce the free energy of ATP hydrolysis to power the mechanical work of substrate translocation across cell membranes. MsbA is an ABC transporter implicated in trafficking lipid A across the inner membrane of Escherichia coli. It has sequence similarity and overlapping substrate specificity with multidrug ABC transporters that export cytotoxic molecules in humans and prokaryotes. Despite rapid advances in structure determination of ABC efflux transporters, little is known regarding the location of substrate-binding sites in the transmembrane segment and the translocation pathway across the membrane. In this study, we have mapped residues proximal to the daunorubicin (DNR)-binding site in MsbA using site-specific, ATP-dependent quenching of DNR intrinsic fluorescence by spin labels. In the nucleotide-free MsbA intermediate, DNR-binding residues cluster at the cytoplasmic end of helices 3 and 6 at a site accessible from the membrane/water interface and extending into an aqueous chamber formed at the interface between the two transmembrane domains. Binding of a nonhydrolyzable ATP analog inverts the transporter to an outward-facing conformation and relieves DNR quenching by spin labels suggesting DNR exclusion from proximity to the spin labels. The simplest model consistent with our data has DNR entering near an elbow helix parallel to the water/membrane interface, partitioning into the open chamber, and then translocating toward the periplasm upon ATP binding.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2679490Documentos Relacionados
- An ATP-Binding Cassette Transporter GhWBC1 from Elongating Cotton Fibers1
- A Novel Bacterial ATP-Binding Cassette Transporter System That Allows Uptake of Macromolecules
- The homodimeric ATP-binding cassette transporter LmrA mediates multidrug transport by an alternating two-site (two-cylinder engine) mechanism
- Vanadate-catalyzed photocleavage of the signature motif of an ATP-binding cassette (ABC) transporter
- A Multifunctional ATP-Binding Cassette Transporter System from Vibrio cholerae Transports Vibriobactin and Enterobactin