Characterization of the iron-sulfur clusters in the nitrogenase-like reductase CfbC/D required for coenzyme F biosynthesis.

Coenzyme F is a nickel-containing tetrapyrrole, serving as the prosthetic group of methyl-coenzyme M reductase in methanogenic and methanotrophic archaea. During coenzyme F biosynthesis, the tetrapyrrole macrocycle is reduced by the nitrogenase-like CfbC/D system consisting of the reductase component CfbC and the catalytic component CfbD. Both components are homodimeric proteins, each carrying a [4Fe-4S] cluster.

Low potential enzymatic hydride transfer via highly cooperative and inversely functionalized flavin cofactors.

Hydride transfers play a crucial role in a multitude of biological redox reactions and are mediated by flavin, deazaflavin or nicotinamide adenine dinucleotide cofactors at standard redox potentials ranging from 0 to -340 mV. 2-Naphthoyl-CoA reductase, a key enzyme of oxygen-independent bacterial naphthalene degradation, uses a low-potential one-electron donor for the two-electron dearomatization of its substrate below the redox limit of known biological hydride transfer processes at E°' = -493 mV. Here we demonstrate by X-ray structural analyses, QM/MM computational studies, and multiple spectroscopy/activity based titrations that highly cooperative electron transfer (n = 3) from a low-potential one-electron (FAD) to a two-electron (FMN) transferring flavin cofactor is the key to overcome the resonance stabilized aromatic system by hydride transfer in a highly hydrophobic pocket.

Apd1 and Aim32 Are Prototypes of Bishistidinyl-Coordinated Non-Rieske [2Fe-2S] Proteins.

Apd1, a cytosolic yeast protein, and Aim32, its counterpart in the mitochondrial matrix, have a C-terminal thioredoxin-like ferredoxin (TLF) domain and a widely divergent N-terminal domain. These proteins are found in bacteria, plants, fungi, and unicellular pathogenic eukaryotes but not in Metazoa. Our chemogenetic experiments demonstrate that the highly conserved cysteine and histidine residues within the C-X-C-X-H-X-G-G-H motif of the TLF domain of Apd1 and Aim32 proteins are essential for viability of yeast cells upon treatment with the redox mediators gallobenzophenone or pyrogallol, respectively.

A Comparison of Prompting Strategies to Teach Intraverbals to an Adolescent with Down Syndrome.

Ingvarsson and Hollobaugh (2011) investigated tact- or echoic-to-intraverbal transfer of stimulus control to "wh" questions for three preschool-aged boys with autism. The current study was a systematic replication of this study with an adolescent girl with Down syndrome. A multielement design was used to compare the effectiveness and efficiency of picture or echoic prompts presented on an iPad or in vivo to teach "wh" questions.