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Canadian researchers investigating how Gram negative bacteria detect and transport metals from the environment, specifically iron, have used NMR to reveal a new structure for a bacterial outer membrane transporter (OMT). The structure of this OMT was not revealed by earlier X-ray structural studies and represents a molecular module that transmits an 'iron availability' signal. Bacteria produce a range of compounds to help them assimilate and utilize iron from their environment. The process starts when an iron compound is sequestered by an OMT, this triggers a signal transduction pathway across the bacterial membrane that interacts with RNA polymerase to induce genetic expression of the required proteins for iron processing. This molecular machinery is complex and far more sophisticated than any synthetic chemical system for extracting and processing a metal from the environment. As such, researchers are interested in understanding how bacteria achieve their great metal-processing efficiency with a view to mimicking this activity or creating engineered microbes tailored to undertake metal extraction for bioremediation and other applications. Biochemical and genetic studies have revealed important clues, but it is only through structural studies, such as diffraction and spectroscopy, that scientists will gain clear insights. Alicia Garcia-Herrero and Hans Vogel of the University of Calgary, Alberta, Canada, have now used NMR spectroscopy to reveal a unique fold in one of the proteins involved in the sequence of iron detection and assimilation, FecA. Previously, FecA from Escherichia coli and FpvA from Pseudomonas aeruginosa were solved using X-ray crystallography. However, those investigators did not resolve electron density for the signalling domains. This the Calgary team suggests may have been due to the domain either being unfolded or flexible relative to the remainder of the protein. The team has now used multidimensional NMR spectroscopy to take a closer look at FecA and have found that its 74 residue N-terminal folds into a tightly packed domain, with two alpha helices sandwiched between two beta sheets. According to structural biologist Susan Buchanan of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, writing in the same issue of Molecular Microbiology, this "represents a unique fold, as no other protein structures showed significant structural similarity." The linker region with the rest of the OMT is, according to the NMR results, unstructured, and so is highly flexible and mobile and can adopt a wide range of conformations. Related links: |
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