IRON TRANSPORT, SYNERGISTIC ANIONS

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are investigating the mechanism of an iron uptake system that is important for survival of pathogenic Staphylococcus aureus in iron-limited media. The Ferric Hydroxamate Uptake ("Fhu") system is able to recognize and assimilate ferric hydroxamate siderophores; it is comprised of an integral membrane ABC transporter complex and peripheral binding proteins, FhuD1 and FhuD2. We are particularly interested in the ferric siderophore binding proteins because they have a high affinity for a structurally diverse collection of siderophores and could be used to deliver antibiotics to the bacteria in a "Trojan Horse" manner. Using SAXS at beamiline ID18, we demonstrated that FhuD1 and FhuD2 undergo only a very small conformational change when they bind ligand. In fact, recent measurements indicate that the extent of the conformational change depends on the exact nature of the siderophore. The role of the siderophore and the binding protein in the transport mechanism are discussed in our publications. Importantly, the structural information provided by SAXS data has led us to conclude that recognition of the ligand by the ABC transport complex is a critical part of the transport mechanism for the Fhu system. We are also using conformational engineering of maltose binding protein (MBP) in E. Coli to assess the relative roles of the binding protein and ligand in triggering ATP hydrolysis by the integral membrane complex. SAXS data obtained at beamline ID18 have been absolutely critical for rapid and accurate evaluation of the effect of our mutations on the conformation of MBP.