Hydrogen bonding rearrangement by a mitochondrial disease mutation in cytochrome bc1 perturbs heme bH redox potential and spin state

Hemes are common elements of biological redox cofactor chains involved in rapid electron transfer. While the redox properties of hemes and the stability of the spin state are recognized as key determinants of their function, understanding the molecular basis of control of these properties is challenging. Here, benefiting from the effects of one mitochondrial disease–related point mutation in cytochrome b, we identify a dual role of hydrogen bonding (H-bond) to the propionate group of heme bH of cytochrome bc1, a common component of energy-conserving systems. We found that replacing conserved glycine with serine in the vicinity of heme bH caused stabilization of this bond, which not only increased the redox potential of the heme but also induced structural and energetic changes in interactions between Fe ion and axial histidine ligands. The latter led to a reversible spin conversion of the oxidized Fe from 1/2 to 5/2, an effect that potentially reduces the electron transfer rate between the heme and its redox partners. We thus propose that H-bond to the propionate group and heme-protein packing contribute to the fine-tuning of the redox potential of heme and maintaining its proper spin state. A subtle balance is needed between these two contributions: While increasing the H-bond stability raises the heme potential, the extent of increase must be limited to maintain the low spin and diamagnetic form of heme. This principle might apply to other native heme proteins and can be exploited in engineering of artificial heme-containing protein maquettes.

New 11,20-Epoxybriaranes from the Gorgonian Coral Junceella fragilis (Ellisellidae)

Two new 11,20-epoxybriaranes, fragilides P (1) and Q (2), as well as two known analogues, robustolide F (3) and juncin Z (4), were obtained from the gorgonian coral Junceella fragilis. The structures, including the absolute configurations of briaranes 1 and 2, were elucidated by using spectroscopic methods and comparing the spectroscopic and rotation data with those of known related analogues. Briarane 4 decreased the generation of superoxide anions by human neutrophils. The propionate group in 1 is rarely found.

Cecal Infusion of Sodium Propionate Promotes Intestinal Development and Jejunal Barrier Function in Growing Pigs

Short-chain fatty acids (SCFAs) produced by microbial fermentation facilitate the differentiation and proliferation of intestinal epithelium. However, the role of individual SCFAs, such as propionate, on intestinal development is still unclear. In the present study, sixteen barrows fitted with a cecal fistula were randomly divided into two groups for cecal infusion of either saline (control group) or sodium propionate (propionate group). After 28 days, the length and the relative weight of intestinal segments were calculated, the intestinal morphology was assessed, and the expression of tight junction protein was measured using qPCR and Western blotting. Compared to the saline group, the length of the colon was significantly increased in the propionate group (p < 0.05). The jejunal villi length and villi/crypt ratio in the propionate group were significantly higher than in the saline group (p < 0.05). Furthermore, propionate infusion significantly upregulated the mRNA levels of Claudin-4 and the expression of Claudin-1, Claudin-4, and Occludin protein in the jejunal mucosa (p < 0.05). Collectively, these findings revealed that the short-chain fatty acid propionate in the hindgut contributed to intestinal development, and selectively enhanced jejunal tight junction protein expression.

Conformational differences between the Pfr and Pr states in Pseudomonas aeruginosa bacteriophytochrome

Phytochromes are red-light photoreceptors that regulate light responses in plants, fungi, and bacteria by means of reversible photoconversion between red (Pr) and far-red (Pfr) light-absorbing states. Here, we report the crystal structure of the Q188L mutant of Pseudomonas aeruginosa bacteriophytochrome (PaBphP) photosensory core module, which exhibits altered photoconversion behavior and different crystal packing from wild type. We observe two distinct chromophore conformations in the Q188L crystal structure that we identify with the Pfr and Pr states. The Pr/Pfr compositions, varying from crystal to crystal, seem to correlate with light conditions under which the Q188L crystals are cryoprotected. We also compare all known Pr and Pfr structures. Using site-directed mutagenesis, we identify residues that are involved in stabilizing the 15Ea (Pfr) and 15Za (Pr) configurations of the biliverdin chromophore. Specifically, Ser-261 appears to be essential to form a stable Pr state in PaBphP, possibly by means of its interaction with the propionate group of ring C. We propose a “flip-and-rotate” model that summarizes the major conformational differences between the Pr and Pfr states of the chromophore and its binding pocket.

Triaqua[3-(4-carboxylatophenoxy)propionato-κO](1,10-phenanthroline-κ2 N,N′)zinc(II)

The title compound, [Zn(C10H8O5)(C12H8N2)(H2O)3], is a neutral mononuclear complex. The Zn atom has a distorted octahedral geometry involving one O atom of the 3-(4-carboxylatophenoxy)propionate group, two N atoms of the 1,10-phenanthroline ligand and three water molecules. Extensive hydrogen-bonding and π–π stacking interactions [centroid–centroid distance = 3.656 (3) Å] construct a three-dimensional supramolecular network.

Transient kinetics of the reaction catalysed by magnesium protoporphyrin IX methyltransferase

Magnesium protoporphyrin IX methyltransferase (ChlM), an enzyme in the chlorophyll biosynthetic pathway, catalyses the transfer of a methyl group to magnesium protoporphyrin IX (MgP) to form magnesium protoporphyrin IX monomethyl ester (MgPME). S-Adenosyl-L-methionine is the other substrate, from which a methyl group is transferred to the propionate group on ring C of the porphyrin macrocycle. Stopped-flow techniques were used to characterize the binding of porphyrin substrate to ChlM from Synechocystis PCC6803 by monitoring tryptophan fluorescence quenching on a millisecond timescale. We concluded that a rapid binding step is preceded by a slower isomerization of the enzyme. Quenched-flow techniques have been employed to characterize subsequent partial reactions in the catalytic mechanism. A lag phase has been identified that has been attributed to the formation of an intermediate. Our results provide a greater understanding of this catalytic process which controls the relative concentrations of MgP and MgPME, both of which are implicated in signalling between the plastid and nucleus in plants.

Reversal by Testosterone of Atrophy of Accessory Genital Glands of Castrated Male Sheep

The histologic features of male accessory genital glands of entire sheep (group I), castrated sheep (group II), castrated sheep treated with 40 daily intramuscular injections of 50 milligrams testosterone propionate (group III), and castrated sheep treated with 600 milligrams testosterone propionate 72 hours before death (group IV) were compared. Sheep were castrated at 3 months old and all sheep were killed when 15 months old. Volume fractions of glandular tissue, intralobular fibromuscular tissue and perilobular fibromuscular tissue of the seminal vesicles and Cowper's glands fluctuated significantly ( P < 0.05) during postcastration atrophy and after repeated testosterone treatment. Atrophy in sheep in group II was least in the prostate but greatest in Cowper's glands, seminal vesicles and ampullae of vasa deferentia. Seminal vesicle plexi, whose cytons had a statistically significant ( P < 0.05) degree of shrinkage, also were atrophied. After treatment with testosterone the postcastration atrophy of plexal neurons was almost reversed in sheep in group III. There also was hypertrophy of epithelial cells but the testosterone treatment failed to reduce to normal the fibromuscular volume fraction of the accessory genital glands. Testosterone propionate treatment of sheep in group IV failed to elicit appreciable morphologic changes. These results are compared with our previous findings on the content and uptake of zinc by the accessory genital glands. It is suggested that accumulation of zinc in the accessory genital glands of sheep is not necessarily closely linked to normal histologic appearance.

Factors determining the sequence of oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III by coproporphyrinogen oxidase in rat liver

Coproporphyrinogen oxidase (EC 1.3.3.3) catalyses the oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III to form protoporphyrinogen IX. A 4-propionate-substituted porphyrinogen, harderoporphyrinogen, which is also a substrate for coproporphyrinogen oxidase, is formed during the reaction. Synthetic [14C]coproporphyrinogens III, specifically labelled in the carboxyl carbon atoms of either the 2- or 4-propionate substituents, were used to measure the rate of decarboxylation of each substituent by rat liver coproporphyrinogen oxidase. The experimental results, together with the recognition that in all known substrates of coproporphyrinogen oxidase only those propionate groups flanked by a specific arrangement of substituents are decarboxylated, indicate that the 4-propionate group of coproporphyrinogen III cannot be attacked until the 2-propionate group has been decarboxylated. Production of 14CO2 from the substrate labelled in the 2-propionate group therefore measures the formation of harderoporphyrinogen, whereas 14CO2 from the 4-propionate-labelled substrate measures protoporphyrinogen IX formation. The rate of harderoporphyrinogen formation is about twice that of protoporphyrinogen, and this ratio is unchanged by varying the concentration of coproporphyrinogen III or by competitive inhibition of the enzyme. When coproporphyrinogen III is present in an excess, two fractions of harderoporphyrinogen can be distinguished. One accumulates during the reaction, and the other, which is destined to become protoporphyrinogen IX, does not equilibrate with added harderoporphyrinogen. It is suggested that both decarboxylations take place at the same active centre, which becomes temporarily inaccessible to coproporphyrinogen III and added harderoporphyrinogen, and that the molecule rotates after the first decarboxylation to allow the second to take place.

Identification of a group of tetracarboxylate porphyrins, containing one acetate and three propionate β-substituents, in faeces from patients with symptomatic cutaneous hepatic porphyria and from rats with porphyria due to hexachlorobenzene

1. Three tetracarboxylate porphyrins, apart from coproporphyrin, were isolated from the faeces of patients with symptomatic cutaneous hepatic porphyria and of rats with porphyria caused by hexachlorobenzene poisoning. The porphyrins were not present in the urine of the porphyric rats or in the faeces of control rats. 2. Two of the porphyrins were identified as tris-(2-carboxyethyl)-carboxymethyl ethyl trimethyl porphin (isocoproporphyrin) and tris-(2-carboxyethyl)-carboxymethyl trimethyl porphin (de-ethyliso-coproporphyrin). 3. The third porphyrin, previously reported to be an analogue of coproporphyrin in which one propionate group is replaced by an α- or β-hydroxypropionate group, was shown to be tris-(2-carboxyethyl)-carboxymethyl-(1-hydroxyethyl)-trimethyl porphin (hydroxyisocoproporphyrin). 4. The order of β-substituents around the porphin ring could not be determined for any of the compounds. 5. Evidence for the existence of a fourth porphyrin, tris-(2-carboxyethyl)-carboxymethyl trimethyl vinyl porphin (dehydroisocoproporphyrin), a postulated precursor of the others, is described. 6. It is suggested that dehydroisocoproporphyrinogen is produced by decarboxylation–dehydrogenation of one of the propionate groups of pentacarboxylate porphyrinogen III.