Bacterial metal detectors.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA.
Molecular Microbiology (Impact Factor: 5.03). 01/2006; 58(5):1205-9. DOI: 10.1111/j.1365-2958.2005.04904.x
Source: PubMed

ABSTRACT Gram negative bacteria can detect environmental iron using outer membrane transporters (OMTs), and then regulate certain transport genes to take advantage of a readily available iron source. This process begins with an iron complex being bound by an OMT, and results in a signal being sent across the outer membrane, the periplasmic space, and the inner membrane, to a sigma factor that interacts with RNA polymerase and initiates transcription of relevant genes. Many of the interactions contributing to signalling have been observed by genetic and biochemical studies, but structural studies, which potentially show these interactions in molecular detail, have been limited. In this issue, Garcia-Herrero and Vogel describe an NMR structure of the periplasmic domain of an OMT, which had not been seen in previous X-ray crystal structures. This domain transmits the 'iron availability' signal to the next protein in the signal transduction cascade, which sits in the inner membrane and extends into the periplasm. The new structure extends our knowledge of transporter architecture and suggests how signalling may occur across the outer membrane.

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    ABSTRACT: Dps proteins are the structural relatives of bacterioferritins and ferritins ubiquitously present in the bacterial and archaeal kingdoms. The ball-shaped enzymes play important roles in the detoxification of ROS (reactive oxygen species), in iron scavenging to prevent Fenton reactions and in the mechanical protection of DNA. Detoxification of ROS and iron chaperoning represent the most archetypical functions of dodecameric Dps enzymes. Recent crystallographic studies of these dodecameric complexes have unravelled species-dependent mechanisms of iron uptake into the hollow spheres. Subsequent functions in iron oxidation at ferroxidase centres are highly conserved among bacteria. Final nucleation of iron as iron oxide nanoparticles has been demonstrated to originate at acidic residues located on the inner surface. Some Dps enzymes are also implicated in newly observed catalytic functions related to the formation of molecules playing roles in bacterium-host cell communication. Most recently, Dps complexes are attracting attention in semiconductor science as biomimetic tools for the technical production of the smallest metal-based quantum nanodots used in nanotechnological approaches, such as memory storage or solar cell development.
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