Analysing the contribution of nucleic acids to the structure and properties of centric heterochromatin

A class of repetitive DNA sequences frequently found at centromeric regions are R/Y-satellites showing an asymmetric distribution of residues resulting in one strand being rich in purines (R-strand) while the complementary strand is pyrimidine-rich (Y-strand). The dodeca-satellite of Drosophila belongs to this class of centromeric satellites. In vitro, the dodeca-satellite forms altered DNA structures in which the R-strand forms very stable intramolecular fold-backs that are stabilised by the formation of tandem G · A mismatches. A single-stranded nucleic acids binding protein, DDP1, binds the unstructured dodeca-satellite Y-strand with high affinity. In polytene chromosomes, DDP1 associates with the heterochromatic chromocenter and, at the euchromatic chromosome arms, co-localises with HP1. DDP1 is a vigilin. Vigilins are highly conserved multi-KH-domain proteins. Scp160p, the vigilin from S. cerevisiae, is involved in the control of ploidy. DDP1 complements a scp160 deletion.     

Mitochondrial-driven bicarbonate transport supports photosynthesis in a marine microalga

The CO(2)-concentrating mechanism (CCM) of the marine eustigmatophycean microalga Nannochloropsis gaditana consists of an active HCO(3)(-) transport system and an internal carbonic anhydrase to facilitate accumulation and conversion of HCO(3)(-) to CO(2) for photosynthetic fixation. Aqueous inlet mass spectrometry revealed that a portion of the CO(2) generated within the cells leaked to the medium, resulting in a significant rise in the extracellular CO(2) concentration to a level above its chemical equilibrium that was diagnostic for active HCO(3)(-) transport. The transient rise in extracellular CO(2) occurred in the light and the dark and was resolved from concurrent respiratory CO(2) efflux using H(13)CO(3)(-) stable isotope techniques. H(13)CO(3)(-) pump-(13)CO(2) leak activity of the CCM was unaffected by 10 microM 3(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of chloroplast linear electron transport, although photosynthetic O(2) evolution was reduced by 90%. However, low concentrations of cyanide, azide, and rotenone along with anoxia significantly reduced or abolished (13)CO(2) efflux in the dark and light. These results indicate that H(13)CO(3)(-) transport was supported by mitochondrial energy production in contrast to other algae and cyanobacteria in which it is supported by photosynthetic electron transport. This is the first report of a direct role for mitochondria in the energization and functioning of the CCM in a photosynthetic organism.     

Calculation of hydrodynamic properties of globular proteins from their atomic-level structure

The solution properties, including hydrodynamic quantities and the radius of gyration, of globular proteins are calculated from their detailed, atomic-level structure, using bead-modeling methodologies described in our previous article (, Biophys. J. 76:3044-3057). We review how this goal has been pursued by other authors in the past. Our procedure starts from a list of atomic coordinates, from which we build a primary hydrodynamic model by replacing nonhydrogen atoms with spherical elements of some fixed radius. The resulting particle, consisting of overlapping spheres, is in turn represented by a shell model treated as described in our previous work. We have applied this procedure to a set of 13 proteins. For each protein, the atomic element radius is adjusted, to fit all of the hydrodynamic properties, taking values close to 3 A, with deviations that fall within the error of experimental data. Some differences are found in the atomic element radius found for each protein, which can be explained in terms of protein hydration. A computational shortcut makes the procedure feasible, even in personal computers. All of the model-building and calculations are carried out with a HYDROPRO public-domain computer program.     

Cerebral Cortex Synaptic Heavy Mitochondria May Represent the Oldest Synaptic Mitochondrial Population: Biochemical Heterogeneity and Effects of L-Acetylcarnitine

The microheterogeneous nature of intrasynaptic mitochondria has been demonstrated and iswidely accepted. However, evidence is still lacking about the role played by the differentintrasynaptic mitochondrial subpopulations. The data obtained support the hypothesis thatheavy mitochondria could represent old mitochondrial populations: in fact, in addition tothe well known impairment of typical mitochondrial functions, they possess the highest levelsof hydroperoxides and their fatty acids pattern is completely modified. The qualitative andquantitative fatty acid modifications suffered by these organelles deeply altered theirprotein/lipid ratio, thus modifying their mode of action. The present work also collects a large bodyof evidence that a subchronic L-acetylcarnitine treatment in 28 days does not structurallyaffect both nonsynaptic and intrasynaptic mitochondria of normal rat in asteady-statemetabolic condition.     

The Relationship between Regular Sports Participation and Vigilance in Male and Female Adolescents

The present study investigated the relationship between regular sport participation (soccer) and vigilance performance. Two groups of male and female adolescents differentiated in terms of their sport participation (athletes, n = 39, and non-athletes, n = 36) took part in the study. In one session, participants performed the Leger Multi-stage fitness test to estimate their aerobic fitness level. In the other session, participants completed the Psychomotor Vigilance Task (PVT) to evaluate their vigilance performance. Perceived arousal prior to the task and motivation toward the task were also measured in the PVT session. The results revealed that athletes had better cardiovascular fitness and showed better performance in the PVT. However, correlation analyses did not show any significant relationship between cardiovascular fitness and performance in the PVT. Athletes showed larger scores in motivation and perceived arousal measures with respect to non-athletes, although, once again, these variables were not correlated with PVT performance. Gender differences were observed only in the Leger test, with males showing greater fitness level than females. The major outcome of this research points to a positive relationship between regular sport participation and vigilance during adolescence. This relationship did not seem to be influenced by gender, perceived arousal, motivation toward the task or cardiovascular fitness. We discuss our results in terms of the different hypotheses put forward in the literature to explain the relationship between physical activity and cognitive functioning.     

Circadian Cycle-Dependent MeCP2 and Brain Chromatin Changes

Methyl CpG binding protein 2 (MeCP2) is a chromosomal protein of the brain, very abundant especially in neurons, where it plays an important role in the regulation of gene expression. Hence it has the potential to be affected by the mammalian circadian cycle. We performed expression analyses of mice brain frontal cortices obtained at different time points and we found that the levels of MeCP2 are altered circadianly, affecting overall organization of brain chromatin and resulting in a circadian-dependent regulation of well-stablished MeCP2 target genes. Furthermore, this data suggests that alterations of MeCP2 can be responsible for the sleeping disorders arising from pathological stages, such as in autism and Rett syndrome.     

Structure of acid beta-glucosidase with pharmacological chaperone provides insight into Gaucher disease

Gaucher disease results from mutations in the lysosomal enzyme acid beta-glucosidase (GCase). Although enzyme replacement therapy has improved the health of some affected individuals, such as those with the prevalent N370S mutation, oral treatment with pharmacological chaperones may be therapeutic in a wider range of tissue compartments by restoring sufficient activity of endogenous mutant GCase. Here we demonstrate that isofagomine (IFG, 1) binds to the GCase active site, and both increases GCase activity in cell lysates and restores lysosomal trafficking in cells containing N370S mutant GCase. We also compare the crystal structures of IFG-bound GCase at low pH with those of glycerol-bound GCase at low pH and apo-GCase at neutral pH. Our data indicate that IFG induces active GCase, which is secured by interactions with Asn370. The design of small molecules that stabilize substrate-bound conformations of mutant proteins may be a general therapeutic strategy for diseases caused by protein misfolding and mistrafficking.     

Depletion of m-type thioredoxin impairs photosynthesis,carbon fixation,and oxidative stress in cyanobacteria

Thioredoxins (Trxs) are disulfide oxidoreductases that regulate many biological processes. The m-type thioredoxin (TrxA) is the only Trx present in all oxygenic photosynthetic organisms. Extensive biochemical and proteomic analyses have identified many TrxA target proteins in different photosynthetic organisms. However, the precise function of this essential protein in vivo is still poorly known. In this study, we generated a conditional Synechocystis sp. PCC 6803 mutant strain (STXA2) using an on-off promoter that is able to survive with only 2% of the TrxA level of the wild-type (WT) strain. STXA2 characterization revealed that TrxA depletion results in growth arrest and pronounced impairment of photosynthesis and the Calvin–Benson–Bassham (CBB) cycle. Analysis of the in vivo redox state of the bifunctional enzyme fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase showed higher levels of oxidation that affected enzyme activity in STXA2. This result implies that TrxA-mediated redox regulation of the CBB cycle is conserved in both cyanobacteria and chloroplasts, although the targets have different evolutionary origins. The STXA2 strain also accumulated more reactive oxygen species and was more sensitive to oxidative stress than the WT. Analysis of the in vivo redox state of 2-Cys peroxiredoxin revealed full oxidation, corresponding with TrxA depletion. Overall, these results indicate that depletion of TrxA in STXA2 greatly alters the cellular redox state, interfering with essential processes such as photosynthetic machinery operativity, carbon assimilation, and oxidative stress response. The TrxA regulatory role appears to be conserved along the evolution of oxygenic photosynthetic organisms.

A cyanobacterial mutant strain with very low TrxA (m-type thioredoxin) content is unable to maintain cellular redox state, affecting the function of essential processes.     

Virgin olive oil and coenzyme Q10 protect heart mitochondria from peroxidative damage during aging.

The mitochondrial theory of aging suggests that this phenomenon is the consequence of random somatic mutations in mitochondrial DNA, induced by long-term exposure to free radical attack. There are two potential dietary means of delaying the effects of free radicals on cellular aging, i.e., enrichment of mitochondrial membranes with monounsaturated fatty acids and supplementation with antioxidants. We have performed a preliminary study on male rats, 6 or 12 month old, fed with diets differing in the nature of the fat (virgin olive oil or sunflower oil) and/or with antioxidant supplementation (coenzyme Q10), analysing hydroperoxide and coenzyme Q9 and Q10 in heart mitochondria. Preliminary results allow us to conclude that the CoQ10 dietetic supplementation as well as the enrichment of the cellular membranes with monounsaturated fatty acids, successfully protect mitochondrial membranes from aged rats against the free radical insult.