期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 295, 期 15, 页码 4974-4984出版社
ELSEVIER
DOI: 10.1074/jbc.RA119.011850
关键词
membrane transport; iron; outer membrane; disulfide; site-directed mutagenesis; siderophore; FepA; fluorescent sensor
资金
- National Science Foundation [MCB09522999]
- National Institutes of Health [GM53836, AI115187]
The Escherichia coli outer membrane receptor FepA transports ferric enterobactin (FeEnt) by an energy- and TonB-dependent, but otherwise a mechanistically undetermined process involving its internal 150-residue N-terminal globular domain (N-domain). We genetically introduced pairs of Cys residues in different regions of the FepA tertiary structure, with the potential to form disulfide bonds. These included Cys pairs on adjacent ?-strands of the N-domain (intra-N) and Cys pairs that bridged the external surface of the N-domain to the interior of the C-terminal transmembrane ?-barrel (inter-N?C). We characterized FeEnt uptake by these mutants with siderophore nutrition tests, [Fe-59]Ent binding and uptake experiments, and fluorescence decoy sensor assays. The three methods consistently showed that the intra-N disulfide bonds, which restrict conformational motion within the N-domain, prevented FeEnt uptake, whereas most inter-N?C disulfide bonds did not prevent FeEnt uptake. These outcomes indicate that conformational rearrangements must occur in the N terminus of FepA during FeEnt transport. They also argue against disengagement of the N-domain out of the channel as a rigid body and suggest instead that it remains within the transmembrane pore as FeEnt enters the periplasm.
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