Guide molecule-driven stereospecific degradation of alpha-methylpolyamines by polyamine oxidase

FAD-dependent polyamine oxidase (PAO; EC 1.5.3.11) is one of the key enzymes in the catabolism of polyamines spermidine and spermine. The natural substrates for the enzyme are N1-acetylspermidine, N1-acetylspermine, and N1,N12-diacetylspermine. Here we report that PAO, which normally metabolizes achiral substrates, oxidized (R)-isomer of 1-amino-8-acetamido-5-azanonane and N1-acetylspermidine as efficiently while (S)-1-amino-8-acetamido-5-azanonane was a much less preferred substrate. It has been shown that in the presence of certain aldehydes, the substrate specificity of PAO and the kinetics of the reaction are changed to favor spermine and spermidine as substrates. Therefore, we examined the effect of several aldehydes on the ability of PAO to oxidize different enantiomers of alpha-methylated polyamines. PAO supplemented with benzaldehyde predominantly catalyzed the cleavage of (R)-isomer of alpha-methylspermidine, whereas in the presence of pyridoxal the (S)-alpha-methylspermidine was preferred. PAO displayed the same stereospecificity with both singly and doubly alpha-methylated spermine derivatives when supplemented with the same aldehydes. Structurally related ketones proved to be ineffective. This is the first time that the stereospecificity of FAD-dependent oxidase has been successfully regulated by changing the supplementary aldehyde. These findings might facilitate the chemical regulation of stereospecificity of the enzymes.     

Identification of a Substrate-binding Site in a Peroxisomal β-Oxidation Enzyme by Photoaffinity Labeling with a Novel Palmitoyl Derivative

Peroxisomes play an essential role in a number of important metabolic pathways including β-oxidation of fatty acids and their derivatives. Therefore, peroxisomes possess various β-oxidation enzymes and specialized fatty acid transport systems. However, the molecular mechanisms of these proteins, especially in terms of substrate binding, are still unknown. In this study, to identify the substrate-binding sites of these proteins, we synthesized a photoreactive palmitic acid analogue bearing a diazirine moiety as a photophore, and performed photoaffinity labeling of purified rat liver peroxisomes. As a result, an 80-kDa peroxisomal protein was specifically labeled by the photoaffinity ligand, and the labeling efficiency competitively decreased in the presence of palmitoyl-CoA. Mass spectrometric analysis identified the 80-kDa protein as peroxisomal multifunctional enzyme type 2 (MFE2), one of the peroxisomal β-oxidation enzymes. Recombinant rat MFE2 was also labeled by the photoaffinity ligand, and mass spectrometric analysis revealed that a fragment of rat MFE2 (residues Trp²⁴⁹ to Arg²⁵¹) was labeled by the ligand. MFE2 mutants bearing these residues, MFE2(W249A) and MFE2(R251A), exhibited decreased labeling efficiency. Furthermore, MFE2(W249G), which corresponds to one of the disease-causing mutations in human MFE2, also exhibited a decreased efficiency. Based on the crystal structure of rat MFE2, these residues are located on the top of a hydrophobic cavity leading to an active site of MFE2. These data suggest that MFE2 anchors its substrate around the region from Trp²⁴⁹ to Arg²⁵¹ and positions the substrate along the hydrophobic cavity in the proper direction toward the catalytic center.     

Synthesis and anti-leishmanial activity of heterocyclic betulin derivatives

Betulin, a naturally occurring abundant triterpene is converted in four steps to 3,28-di-O-acetyllupa-12,18-diene. When various 4-substituted urazoles were oxidized to the corresponding urazines with iodobenzene diacetate in the presence of 3,28-di-O-acetyllupa-12,18-diene, new heterocyclic betulin derivatives were produced. These betulin derivatives were examined in a microplate assay at 50 μM for their ability to inhibit the growth of Leishmania donovani axenic amastigotes, a species that causes the fatal visceral leishmaniasis. GI₅₀ (concentration for 50% growth inhibition) values of the most effective compounds were determined and their cytotoxicity on the human macrophage cell line THP-1 evaluated. The anti-leishmanial activity on L. donovani amastigotes growing in macrophages was also examined. The heterocycloadduct between 3,28-di-O-acetyllupa-12,18-diene and 4-methylurazine was the most effective derivative with an GI₅₀ = 8.9 μM against L. donovani amastigotes.     

FAS haploinsufficiency is a common disease mechanism in the human autoimmune lymphoproliferative syndrome

The autoimmune lymphoproliferative syndrome (ALPS) is characterized by early-onset lymphadenopathy, splenomegaly, immune cytopenias, and an increased risk for B cell lymphomas. Most ALPS patients harbor mutations in the FAS gene, which regulates lymphocyte apoptosis. These are commonly missense mutations affecting the intracellular region of the protein and have a dominant-negative effect on the signaling pathway. However, analysis of a large cohort of ALPS patients revealed that ～30% have mutations affecting the extracellular region of FAS, and among these, 70% are nonsense, splice site, or insertions/deletions with frameshift for which no dominant-negative effect would be expected. We evaluated the latter patients to understand the mechanism(s) by which these mutations disrupted the FAS pathway and resulted in clinical disease. We demonstrated that most extracellular-region FAS mutations induce low FAS expression due to nonsense-mediated RNA decay or protein instability, resulting in defective death-inducing signaling complex formation and impaired apoptosis, although to a lesser extent as compared with intracellular mutations. The apoptosis defect could be corrected by FAS overexpression in vitro. Our findings define haploinsufficiency as a common disease mechanism in ALPS patients with extracellular FAS mutations.     

Determination of aspartase activity in dairy Propionibacterium strains

Propionic acid bacteria (PAB) are important as starter cultures for the dairy industry in the manufacture of Swiss-type cheeses, in which they are involved in the formation of eyes and are responsible for the typical flavour and aroma. These characteristics are mainly due to the classical propionic acid fermentation, but also the conversion of aspartate to fumarate and ammonia by the enzyme aspartase and the subsequent reduction of fumarate to succinate, which occur in dairy Propionibacterium freudenreichii ssp. shermanii and ssp. freudenreichii starter strains. Additionally, the metabolism of free amino acids may be partly responsible for secondary fermentation and the subsequent split defects in cheese matrix. Here a method for aspartase activity was established and a number of dairy propionibacteria belonging to P. freudenreichii ssp. shermanii and freudenreichii were screened for this enzyme activity. A wide range of aspartase activity could be found in PAB isolates originating from cheese. The majority, i.e. 70% of the 100 isolates tested, showed very low levels of aspartate activity.     

Heritability of submaximal exercise heart rate response to exercise training is accounted for by nine SNPs

Endurance training-induced changes in hemodynamic traits are heritable. However, few genes associated with heart rate training responses have been identified. The purpose of our study was to perform a genome-wide association study to uncover DNA sequence variants associated with submaximal exercise heart rate training responses in the HERITAGE Family Study. Heart rate was measured during steady-state exercise at 50 W (HR50) on 2 separate days before and after a 20-wk endurance training program in 483 white subjects from 99 families. Illumina HumanCNV370-Quad v3.0 BeadChips were genotyped using the Illumina BeadStation 500GX platform. After quality control procedures, 320,000 single-nucleotide polymorphisms (SNPs) were available for the genome-wide association study analyses, which were performed using the MERLIN software package (single-SNP analyses and conditional heritability tests) and standard regression models (multivariate analyses). The strongest associations for HR50 training response adjusted for age, sex, body mass index, and baseline HR50 were detected with SNPs at the YWHAQ locus on chromosome 2p25 (P = 8.1 × 10(-7)), the RBPMS locus on chromosome 8p12 (P = 3.8 × 10(-6)), and the CREB1 locus on chromosome 2q34 (P = 1.6 × 10(-5)). In addition, 37 other SNPs showed P values <9.9 × 10(-5). After removal of redundant SNPs, the 10 most significant SNPs explained 35.9% of the ΔHR50 variance in a multivariate regression model. Conditional heritability tests showed that nine of these SNPs (all intragenic) accounted for 100% of the ΔHR50 heritability. Our results indicate that SNPs in nine genes related to cardiomyocyte and neuronal functions, as well as cardiac memory formation, fully account for the heritability of the submaximal heart rate training response.     

Recrystallisation behaviour of native and processed waxy maize starch in relation to the molecular characteristics

Molecular characteristics were determined for native waxy maize starch and maize starch modified in different way (by mechanical treatment or/and acid hydrolysis). Recrystallisation behaviour was studied. Methods used in this study were MALLS, HPAEC-PAD, NMR, DSC, SEM, light microscopy.

Five starch materials were subjected to storage under the same conditions in the presence of water (70 w/w%). Molecular weight, radius of gyration, initial crystallinity, and degree of polymerisation, degree of branching, chain length distribution profiles, were related to nucleation rate during the recrystallisation process, rate of recrystallisation, thermal stability and amount of obtained crystallinity. This allowed the following connections between the molecular characteristics and kinetic of recrystallisation to be proposed: Amylopectin molecular weight appeared to affect the number of starch crystallites formed and amount of crystallinity but not the stability of the rebuilt crystallites. The stability of rebuilt crystallites can be controlled by degree of polymerization, degree of branching and unit chain length distribution, characteristics which were similar for the starches.

A mixture of two starches, with and without crystalline structure in initial state but with molecular weight in same range, were stored and scanned in order to understand possible cocrystallisation effects.