Roles of acyl carrier proteins in ladderane fatty acid producing-organisms.

Ladderanes are highly strained hydrocarbons consisting of two or more linearly concatenated cyclobutane rings. Strikingly, ladderane moieties are part of unique fatty acids and fatty alcohols that are exclusively found in the membrane lipids of anaerobic ammonium-oxidizing (anammox) bacteria. These bacteria express a distinctive gene cluster (cluster I) that has been suggested to be responsible for ladderane fatty acid (FA) biosynthesis in addition to a cluster likely involved in canonical FA biosynthesis (cluster III).

Highly oxygenated antiplasmodial and non-hemolytic Δ stigmastane-type steroids from the twigs of Vernonia amygdalina Delile.

Chemical investigations of a methanolic extract of the twigs of Vernonia amygdalina Delile (Asteraceae) resulted in the isolation and identification of three previously undescribed highly oxygenated Δ stigmastane-type steroids namely vernonins U-W (1-3) along with six known compounds (4-9). The structural characterization of all the isolated compounds has been conducted via comprehensive 1D and 2D-NMR spectroscopy as well as HRMS. The seven steroidal derivatives 1-7 were evaluated for their antiplasmodial activity against the chloroquine-resistant strain P.

Structures of an unusual 3-hydroxyacyl dehydratase (FabZ) from a ladderane-producing organism with an unexpected substrate preference.

The genomes of anaerobic ammonium-oxidizing (anammox) bacteria contain a gene cluster comprising genes of unusual fatty acid biosynthesis enzymes that were suggested to be involved in the synthesis of the unique "ladderane" lipids produced by these organisms. This cluster encodes an acyl carrier protein (denoted as "amxACP") and a variant of FabZ, an ACP-3-hydroxyacyl dehydratase. In this study, we characterize this enzyme, which we call anammox-specific FabZ ("amxFabZ"), to investigate the unresolved biosynthetic pathway of ladderane lipids.

Neodymium as Metal Cofactor for Biological Methanol Oxidation: Structure and Kinetics of an XoxF1-Type Methanol Dehydrogenase.

The methane-oxidizing bacterium Methylacidimicrobium thermophilum AP8 thrives in acidic geothermal ecosystems that are characterized by high degassing of methane (CH), H, HS, and by relatively high lanthanide concentrations. Lanthanides (atomic numbers 57 to 71) are essential in a variety of high-tech devices, including mobile phones. Remarkably, the same elements are actively taken up by methanotrophs/methylotrophs in a range of environments, since their XoxF-type methanol dehydrogenases require lanthanides as a metal cofactor.

Specificity of Small -Type Cytochromes in Anaerobic Ammonium Oxidation.

Anaerobic ammonium oxidation (anammox) is a bacterial process in which ammonium and nitrite are combined into dinitrogen gas and water, yielding energy for the cell. This process relies on a series of redox reactions catalyzed by a set of enzymes, with electrons being shuttled to and from these enzymes, likely by small cytochrome proteins. For this system to work productively, these electron carriers require a degree of specificity toward the various possible redox partners they encounter in the cell.

Dynamics in an unusual acyl carrier protein from a ladderane lipid-synthesizing organism.

Anaerobic ammonium-oxidizing (anammox) bacteria express a distinct acyl carrier protein implicated in the biosynthesis of the highly unusual "ladderane" lipids these organisms produce. This "anammox-specific" ACP, or amxACP, shows several unique features such as a conserved FF motif and an unusual sequence in the functionally important helix III. Investigation of the protein's structure and dynamics, both in the crystal by ensemble refinement and by MD simulations, reveals that helix III adopts a rare six-residue-long 3 -helical conformation that confers a large degree of conformational and positional variability on this part of the protein.

Purification of the key enzyme complexes of the anammox pathway from DEMON sludge.

Anaerobic Ammonium Oxidation ("anammox") is a bacterial process in which nitrite and ammonium are converted into nitrogen gas and water, yielding energy for the cell. Anammox is an important branch of the global biological nitrogen cycle, being responsible for up to 50% of the yearly nitrogen removal from the oceans. Strikingly, the anammox process uniquely relies on the extremely reactive and toxic compound hydrazine as a free intermediate.

Structure of the 4-hydroxy-tetrahydrodipicolinate synthase from the thermoacidophilic methanotroph Methylacidiphilum fumariolicum SolV and the phylogeny of the aminotransferase pathway.

The enzyme 4-hydroxy-tetrahydrodipicolinate synthase (DapA) is involved in the production of lysine and precursor molecules for peptidoglycan synthesis. In a multistep reaction, DapA converts pyruvate and L-aspartate-4-semialdehyde to 4-hydroxy-2,3,4,5-tetrahydrodipicolinic acid. In many organisms, lysine binds allosterically to DapA, causing negative feedback, thus making the enzyme an important regulatory component of the pathway.

A nitric oxide-binding heterodimeric cytochrome complex from the anammox bacterium binds to hydrazine synthase.

Anaerobic ammonium oxidation (anammox) is a microbial process responsible for significant nitrogen loss from the oceans and other ecosystems. The redox reactions at the heart of anammox are catalyzed by large multiheme enzyme complexes that rely on small cytochrome proteins for electron shuttling. Among the most highly abundant of these cytochromes is a unique heterodimeric complex composed of class I and class II -type cytochromes called NaxLS, which has distinctive biochemical and spectroscopic properties.

A 60-heme reductase complex from an anammox bacterium shows an extended electron transfer pathway.

The hydroxylamine oxidoreductase/hydrazine dehydrogenase (HAO/HDH) protein family constitutes an important group of octaheme cytochromes c (OCCs). The majority of these proteins form homotrimers, with their subunits being covalently attached to each other via a rare cross-link between the catalytic heme moiety and a conserved tyrosine residue in an adjacent subunit. This covalent cross-link has been proposed to modulate the active-site heme towards oxidative catalysis by distorting the heme plane.

Similar but Not the Same: First Kinetic and Structural Analyses of a Methanol Dehydrogenase Containing a Europium Ion in the Active Site.

Since the discovery of the biological relevance of rare earth elements (REEs) for numerous different bacteria, questions concerning the advantages of REEs in the active sites of methanol dehydrogenases (MDHs) over calcium(II) and of why bacteria prefer light REEs have been a subject of debate. Here we report the cultivation and purification of the strictly REE-dependent methanotrophic bacterium Methylacidiphilum fumariolicum SolV with europium(III), as well as structural and kinetic analyses of the first methanol dehydrogenase incorporating Eu in the active site. Crystal structure determination of the Eu-MDH demonstrated that overall no major structural changes were induced by conversion to this REE.

Characterization of Anammox Hydrazine Dehydrogenase, a Key N2-producing Enzyme in the Global Nitrogen Cycle.

Anaerobic ammonium-oxidizing (anammox) bacteria derive their energy for growth from the oxidation of ammonium with nitrite as the electron acceptor. N2, the end product of this metabolism, is produced from the oxidation of the intermediate, hydrazine (N2H4). Previously, we identified N2-producing hydrazine dehydrogenase (KsHDH) from the anammox organism Kuenenia stuttgartiensis as the gene product of kustc0694 and determined some of its catalytic properties.

The inner workings of the hydrazine synthase multiprotein complex.

Anaerobic ammonium oxidation (anammox) has a major role in the Earth's nitrogen cycle and is used in energy-efficient wastewater treatment. This bacterial process combines nitrite and ammonium to form dinitrogen (N2) gas, and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans. Strikingly, the anammox process relies on the highly unusual, extremely reactive intermediate hydrazine, a compound also used as a rocket fuel because of its high reducing power.

An unexpected reactivity of the P460 cofactor in hydroxylamine oxidoreductase.

Hydroxylamine oxidoreductases (HAOs) contain a unique haem cofactor called P460 that consists of a profoundly ruffled c-type haem with two covalent bonds between the haem porphyrin and a conserved tyrosine. This cofactor is exceptional in that it abstracts electrons from a ligand bound to the haem iron, whereas other haems involved in redox chemistry usually inject electrons into their ligands. The effects of the tyrosine cross-links and of the haem ruffling on the chemistry of this cofactor have been investigated theoretically but are not yet clear.

Structural basis of biological NO generation by octaheme oxidoreductases.

Nitric oxide is an important molecule in all domains of life with significant biological functions in both pro- and eukaryotes. Anaerobic ammonium-oxidizing (anammox) bacteria that contribute substantially to the release of fixed nitrogen into the atmosphere use the oxidizing power of NO to activate inert ammonium into hydrazine (N2H4). Here, we describe an enzyme from the anammox bacterium Kuenenia stuttgartiensis that uses a novel pathway to make NO from hydroxylamine.

Rare earth metals are essential for methanotrophic life in volcanic mudpots.

Growth of Methylacidiphilum fumariolicum SolV, an extremely acidophilic methanotrophic microbe isolated from an Italian volcanic mudpot, is shown to be strictly dependent on the presence of lanthanides, a group of rare earth elements (REEs) such as lanthanum (Ln), cerium (Ce), praseodymium (Pr) and neodymium (Nd). After fractionation of the bacterial cells and crystallization of the methanol dehydrogenase (MDH), it was shown that lanthanides were essential as cofactor in a homodimeric MDH comparable with one of the MDHs of Methylobacterium extorquens AM1. We hypothesize that the lanthanides provide superior catalytic properties to pyrroloquinoline quinone (PQQ)-dependent MDH, which is a key enzyme for both methanotrophs and methylotrophs.

¹H, ¹³C, and ¹⁵N chemical shift assignments of the phosphotyrosine binding domain 2 (PTB2) of human FE65.

Phosphotyrosine binding domains (PTB) are protein-protein interaction domains that play important roles in various cellular signal transduction pathways. The second phosphotyrosine binding domain (PTB2) of the human scaffolding protein FE65 interacts with the C-terminal part of the Amyloid Precursor Protein (APP) involved in Alzheimer's disease. The structure of PTB2 in complex with a 32 amino acid fragment of APP has been solved previously by X-ray crystallography.

Phosphorylation of LRP1 regulates the interaction with Fe65.

Neuronal Fe65 is a central adapter for the intracellular protein network of Alzheimer's disease related amyloid precursor protein (APP). It contains a unique tandem array of phosphotyrosine-binding (PTB) domains that recognize NPXY internalization motifs present in the intracellular domains of APP (AICD) and the low-density lipoprotein receptor-related protein LRP1 (LICD). The ternary APP/Fe65/LRP1 complex is an important mediator of APP processing and affects β-amyloid peptide production.