Structure and Mechanism of the Siderophore-Interacting Protein from the Fuscachelin Gene Cluster of <i>Thermobifida fusca</i>

Microbial iron acquisition is a complex process and frequently a key and necessary step for survival. Among the several paths for iron assimilation, small molecule siderophore-mediated transport is a commonly employed strategy of many microorganisms. The chemistry and biology of the extraordinary tight and specific binding of siderophores to metal is also exploited in therapeutic treatments for microbial virulence and metal toxicity. The intracellular fate of iron acquired via the siderophore pathway is one of the least understood steps in the complex process at the molecular level. A common route to cellular incorporation is the single-electron reduction of ferric to ferrous iron catalyzed by specific and/or nonspecific reducing agents. The biosynthetic gene clusters for siderophores often contain representatives of one or two families of redox-active enzymes: the flavin-containing “siderophore-interacting protein” and iron–sulfur ferric siderophore reductases. Here we present the structure and characterization of the siderophore-interacting protein, FscN, from the fuscachelin siderophore gene cluster of <i>Thermobifida fusca</i>. The structure shows a flavoreductase fold with a noncovalently bound FAD cofactor along with an unexpected metal bound adjacent to the flavin site. We demonstrated that FscN is redox-active and measured the binding and reduction of ferric fuscachelin. This work provides a structural basis for the activity of a siderophore-interacting protein and further insight into the complex and important process of iron acquisition and utilization

Interdomain and Intermodule Organization in Epimerization Domain Containing Nonribosomal Peptide Synthetases

Nonribosomal peptide synthetases are large, complex multidomain enzymes responsible for the biosynthesis of a wide range of peptidic natural products. Inherent to synthetase chemistry is the thioester templated mechanism that relies on protein/protein interactions and interdomain dynamics. Several questions related to structure and mechanism remain to be addressed, including the incorporation of accessory domains and intermodule interactions. The inclusion of nonproteinogenic d-amino acids into peptide frameworks is a common and important modification for bioactive nonribosomal peptides. Epimerization domains, embedded in nonribosomal peptide synthetases assembly lines, catalyze the l- to d-amino acid conversion. Here we report the structure of the epimerization domain/peptidyl carrier protein didomain construct from the first module of the cyclic peptide antibiotic gramicidin synthetase. Both <i>holo</i> (phosphopantethiene post-translationally modified) and <i>apo</i> structures were determined, each representing catalytically relevant conformations of the two domains. The structures provide insight into domain–domain recognition, substrate delivery during the assembly line process, in addition to the structural organization of homologous condensation domains, canonical players in all synthetase modules

Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio for the study cohort.

<p>Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio for the study cohort.</p

Cumulative incidence of subsequent essential tremor in the comparison and migraine cohorts.

<p>Cumulative incidence of subsequent essential tremor in the comparison and migraine cohorts.</p

Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio for the study cohort stratified by age, sex, and comorbidities.

<p>Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio for the study cohort stratified by age, sex, and comorbidities.</p

Summary of previous studies examining the association between migraine and ET.

<p>Summary of previous studies examining the association between migraine and ET.</p

Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio by various tiers of frequency of annual medical visits related to migraine.

<p>Incidence of subsequent essential tremor and multivariate Cox proportional hazards regression analysis measured hazard ratio by various tiers of frequency of annual medical visits related to migraine.</p

Increased risk of essential tremor in migraine: A population-based retrospective cohort study

<div><p>Purpose</p><p>To examine the long-term risk of essential tremor (ET) in migraine.</p><p>Methods</p><p>Using population-based administrative data from a subset of the National Health Insurance Research Database (NHIRD) of Taiwan, we identified 22,696 newly diagnosed migraineurs (mean age 44.5 years) and a matched migraine-free cohort of 90,784 individuals in the period 2000–2008. Multivariable Cox proportional hazards regression analysis was conducted for assessing the ET risk for the migraine cohort compared to the migraine-free cohort.</p><p>Results</p><p>After adjusting for covariates, the migraine cohort had a 1.83-fold increased risk (95% CI 1.50–2.23) of subsequent ET in comparison to the migraine-free cohort (8.97 vs. 4.81 per 10,000 person-years). In the subgroup analysis, patients with migraine were associated with higher risks of ET, regardless of gender, age or the existence of comorbidities.</p><p>Conclusion</p><p>Our findings demonstrated an association between migraine and ET, suggesting a possible shared pathophysiology underpinning both disorders.</p></div

Identification of a Novel Epoxyqueuosine Reductase Family by Comparative Genomics

The reduction of epoxyqueuosine (oQ) is the last step in the synthesis of the tRNA modification queuosine (Q). While the epoxyqueuosine reductase (EC 1.17.99.6) enzymatic activity was first described 30 years ago, the encoding gene <i>queG</i> was only identified in <i>Escherichia coli</i> in 2011. Interestingly, <i>queG</i> is absent from a large number of sequenced genomes that harbor Q synthesis or salvage genes, suggesting the existence of an alternative epoxyqueuosine reductase in these organisms. By analyzing phylogenetic distributions, physical gene clustering, and fusions, members of the Domain of Unknown Function 208 (DUF208) family were predicted to encode for an alternative epoxyqueuosine reductase. This prediction was validated with genetic methods. The Q modification is present in <i>Lactobacillus salivarius</i>, an organism missing <i>queG</i> but harboring the <i>duf208</i> gene. <i>Acinetobacter baylyi</i> ADP1 is one of the few organisms that harbor both QueG and DUF208, and deletion of both corresponding genes was required to observe the absence of Q and the accumulation of oQ in tRNA. Finally, the conversion oQ to Q was restored in an <i>E. coli queG</i> mutant by complementation with plasmids harboring <i>duf208</i> genes from different bacteria. Members of the DUF208 family are not homologous to QueG enzymes, and thus, <i>duf208</i> is a non-orthologous replacement of <i>queG</i>. We propose to name DUF208 encoding genes as <i>queH</i>. While QueH contains conserved cysteines that could be involved in the coordination of a Fe/S center in a similar fashion to what has been identified in QueG, no cobalamin was identified associated with recombinant QueH protein

T-value significance maps of the association between homocysteine and mean diffusivity (MD).

<p>voxel-based DTI analysis showing a significant positive correlation between the level of homocysteine and MD in the bilateral cerebellar peduncles, the brainstem, the bilateral anterior temporal WM, and the genu of the corpus callosum (in red). The number indicates the z-axis coordinate in MNI space (unit in mm). R: right, L: left.</p