B-type natriuretic peptide predicts new-onset atrial fibrillation in patients with ST-segment elevation myocardial infarction treated by primary percutaneous coronary intervention

The predictive value of B-type natriuretic peptide (BNP) with respect to the occurrence of new-onset atrial fibrillation (AF) in patients with ST-segment elevation myocardial infarction (STEMI) treated by primary percutaneous coronary intervention (PCI) is unknown. The aim of this study was to evaluate whether BNP has a predictive value for the occurrence of new-onset AF in patients with STEMI treated by primary PCI. In 180 patients with STEMI treated by primary PCI, BNP concentrations were measured 24h after chest pain onset. The Receiver Operating Characteristic analysis was performed to identify the most useful BNP cut-off level for the prediction of AF. The patients were divided into the two groups according to calculated cut-off level: high BNP group (BNP≥720 pg/mL, n=33) and low BNP group (BNP<720 pg/mL, n=147). The incidence of AF was 5.0%, and occurred more frequently in high BNP group (7/33, 21.2%) than in low BNP group (2/147, 1.4%), (p<0.001). Patients with high BNP were older (p=0.017), had more often anterior wall infarction (p=0.015), higher Killip class on admission (p=0.038), higher peak troponin I (p=0.002), lower left ventricular ejection fraction (p=0.029) than patients with low BNP. After multivariate adjustment, BNP was an independent predictor of AF (OR 3.70, 95% CI 1.40-9.77, p=0.008). BNP independently predicts the occurrence of new-onset AF in STEMI patients treated by primary PCI.     

Evolution and diversity of clonal bacteria: the paradigm of Mycobacterium tuberculosis

Background

Mycobacterium tuberculosis complex species display relatively static genomes and 99.9% nucleotide sequence identity. Studying the evolutionary history of such monomorphic bacteria is a difficult and challenging task.

Principal Findings

We found that single-nucleotide polymorphism (SNP) analysis of DNA repair, recombination and replication (3R) genes in a comprehensive selection of M. tuberculosis complex strains from across the world, yielded surprisingly high levels of polymorphisms as compared to house-keeping genes, making it possible to distinguish between 80% of clinical isolates analyzed in this study. Bioinformatics analysis suggests that a large number of these polymorphisms are potentially deleterious. Site frequency spectrum comparison of synonymous and non-synonymous variants and Ka/Ks ratio analysis suggest a general negative/purifying selection acting on these sets of genes that may lead to suboptimal 3R system activity. In turn, the relaxed fidelity of 3R genes may allow the occurrence of adaptive variants, some of which will survive. Furthermore, 3R-based phylogenetic trees are a new tool for distinguishing between M. tuberculosis complex strains.

Conclusions/Significance

This situation, and the consequent lack of fidelity in genome maintenance, may serve as a starting point for the evolution of antibiotic resistance, fitness for survival and pathogenicity, possibly conferring a selective advantage in certain stressful situations. These findings suggest that 3R genes may play an important role in the evolution of highly clonal bacteria, such as M. tuberculosis. They also facilitate further epidemiological studies of these bacteria, through the development of high-resolution tools. With many more microbial genomes being sequenced, our results open the door to 3R gene-based studies of adaptation and evolution of other, highly clonal bacteria.     

Genetic analysis of mutagenesis in aging Escherichia coli colonies

Bacteria live in unstructured and structured environments, experiencing feast and famine lifestyles. Bacterial colonies can be viewed as model structured environments. SOS induction and mutagenesis have been observed in aging Escherichia coli colonies, in the absence of exogenous sources of DNA damage. This cAMP-dependent mutagenesis occurring in Resting Organisms in a Structured Environment (ROSE) is unaffected by a umuC mutation and therefore differs from both targeted UV mutagenesis and recA730 (SOS constitutive) untargeted mutagenesis. As a recB mutation has only a minor effect on ROSE mutagenesis it also differs from both adaptive reversion of the lacI33 allele and from iSDR (inducible Stable DNA Replication) mutagenesis. Besides its recA and lexA dependence, ROSE mutagenesis is also uvrB and polA dependent. These genetic requirements are reminiscent of the untargeted mutagenesis in λ phage observed when unirradiated λ infects UV-irradiated E. coli. These mutations, which are not observed in aging liquid cultures, accumulate linearly with the age of the colonies. ROSE mutagenesis might offer a good model for bacterial mutagenesis in structured environments such as biofilms and for mutagenesis of quiescent eukaryotic cells.     

Phosphorylation of SUMO-1 occurs in vivo and is conserved through evolution

Protein dynamics is regulated by an elaborate interplay between different post-translational modifications. Ubiquitin and ubiquitin-like proteins (Ubls) are small proteins that are covalently conjugated to target proteins with important functional consequences. One such modifier is SUMO, which mainly modifies nuclear proteins. SUMO contains a unique N-terminal arm not present in ubiquitin and other Ubls, which functions in the formation of SUMO polymers. Here, we unambiguously show that serine 2 of the endogenous SUMO-1 N-terminal protrusion is phosphorylated in vivo using very high mass accuracy mass spectrometry at both the MS and the MS/MS level and complementary fragmentation techniques. Strikingly, we detected the same phosphorylation in yeast, Drosophila and human cells, suggesting an evolutionary conserved function for this modification. The nearly identical human SUMO-2 and SUMO-3 isoforms differ in serine 2; thus, only SUMO-3 could be phosphorylated at this position. Our finding that SUMO can be modified may point to an additional level of complexity through modifying a protein-modifier.     

In vivo identification of human small ubiquitin-like modifier polymerization sites by high accuracy mass spectrometry and an in vitro to in vivo strategy

The length and precise linkage of polyubiquitin chains is important for their biological activity. Although other ubiquitin-like proteins have the potential to form polymeric chains their identification in vivo is challenging and their functional role is unclear. Vertebrates express three small ubiquitin-like modifiers, SUMO-1, SUMO-2, and SUMO-3. Mature SUMO-2 and SUMO-3 are nearly identical and contain an internal consensus site for sumoylation that is missing in SUMO-1. Combining state-of-the-art mass spectrometry with an "in vitro to in vivo" strategy for post-translational modifications, we provide direct evidence that SUMO-1, SUMO-2, and SUMO-3 form mixed chains in cells via the internal consensus sites for sumoylation in SUMO-2 and SUMO-3. In vitro, the chain length of SUMO polymers could be influenced by changing the relative amounts of SUMO-1 and SUMO-2. The developed methodology is generic and can be adapted for the identification of other sumoylation sites in complex samples.     

The ubiquitin-proteasome system is a key component of the SUMO-2/3 cycle

Many proteins are regulated by a variety of post-translational modifications, and orchestration of these modifications is frequently required for full control of activity. Currently little is known about the combinatorial activity of different post-translational modifications. Here we show that extensive cross-talk exists between sumoylation and ubiquitination. We found that a subset of SUMO-2-conjugated proteins is subsequently ubiquitinated and degraded by the proteasome. In a screen for preferential SUMO-1 or SUMO-2 target proteins, we found that ubiquitin accumulated in purified SUMO-2 conjugates but not in SUMO-1 conjugates. Upon inhibition of the proteasome, the amount of ubiquitin in purified SUMO-2 conjugates increased. In addition, we found that endogenous SUMO-2/3 conjugates, but not endogenous SUMO-1 conjugates, accumulated in response to proteasome inhibitors. Quantitative proteomics experiments enabled the identification of 73 SUMO-2-conjugated proteins that accumulated in cells treated with proteasome inhibitors. Cross-talk between SUMO-2/3 and the ubiquitin-proteasome system controls many target proteins that regulate all aspects of nucleic acid metabolism. Surprisingly the relative abundance of 40 SUMO-2-conjugated proteins was reduced by proteasome inhibitors possibly because of a lack of recycled SUMO-2. We conclude that SUMO-2/3 conjugation and the ubiquitin-proteasome system are tightly integrated and act in a cooperative manner.     

Interaction between phosphofructokinase and aldolase from Saccharomyces cerevisiae studied by aqueous two-phase partitioning

Phosphofructokinase (EC 2.7.1.11) and aldolase (EC 4.1.2.13) have been highly purified from Saccharomyces cerevisiae by improved protocols. Partitioning of the enzymes in aqueous polymer two-phase systems was used to detect complex formation. The partition of each enzyme was found to be affected by the presence of the other enzyme. AMP affected the partition of the individual enzymes as well as the mixture of the two. The activities of the respective enzymes were stimulated in the putative complex in an AMP-dependent manner. Two strictly conserved residues belonging to an acidic surface loop of class II aldolases, are a potential site for electrostatic interaction with the positively charged regions close to the active site in phosphofructokinase.