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Survival after hospital discharge for ST-segment elevation and non-ST-segment elevation acute myocardial infarction: a population-based study

Thu, 01/15/2015 - 2:42pm

BACKGROUND: Limited recent data are available describing differences in long-term survival, and factors affecting prognosis, after ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction (NSTEMI), especially from the more generalizable perspective of a population-based investigation. The objectives of this study were to examine differences in post-discharge prognosis after hospitalization for STEMI and NSTEMI, with a particular focus on factors associated with reduced long-term survival.

METHODS: We reviewed the medical records of residents of the Worcester, MA, USA metropolitan area hospitalized at eleven central Massachusetts medical centers for acute myocardial infarction (AMI) during 2001, 2003, 2005, and 2007.

RESULTS: A total of 3762 persons were hospitalized with confirmed AMI; of these, 2539 patients (67.5%) were diagnosed with NSTEMI. The average age of study patients was 70.3 years and 42.9% were women. Patients with NSTEMI experienced higher post-discharge death rates with 3-month, 1-year, and 2-year death rates of 12.6%, 23.5%, and 33.2%, respectively, compared to 6.1%, 11.5%, and 16.4% for patients with STEMI. After multivariable adjustment, patients with NSTEMI were significantly more likely to have died after hospital discharge (adjusted hazards ratio 1.28; 95% confidence interval 1.14-1.44). Several demographic (eg, older age) and clinical (eg, history of stroke) factors were associated with reduced long-term survival in patients with NSTEMI and STEMI.

CONCLUSIONS: The results of this study in residents of central Massachusetts suggest that patients with NSTEMI are at higher risk for dying after hospital discharge, and several subgroups are at particularly increased risk.

Blasticidin S inhibits translation by trapping deformed tRNA on the ribosome

Thu, 01/15/2015 - 2:42pm

The antibiotic blasticidin S (BlaS) is a potent inhibitor of protein synthesis in bacteria and eukaryotes. We have determined a 3.4-A crystal structure of BlaS bound to a 70StRNA ribosome complex and performed biochemical and single-molecule FRET experiments to determine the mechanism of action of the antibiotic. We find that BlaS enhances tRNA binding to the P site of the large ribosomal subunit and slows down spontaneous intersubunit rotation in pretranslocation ribosomes. However, the antibiotic has negligible effect on elongation factor G catalyzed translocation of tRNA and mRNA. The crystal structure of the antibiotic-ribosome complex reveals that BlaS impedes protein synthesis through a unique mechanism by bending the 3' terminus of the P-site tRNA toward the A site of the large ribosomal subunit. Biochemical experiments demonstrate that stabilization of the deformed conformation of the P-site tRNA by BlaS strongly inhibits peptidyl-tRNA hydrolysis by release factors and, to a lesser extent, peptide bond formation.

Successful treatment of mobile right atrial thrombus and acute pulmonary embolism with intravenous tissue plasminogen activator

Thu, 01/15/2015 - 2:42pm

An 89-year-old woman came with symptoms of progressively worsening dyspnoea at rest over the preceding week. She was normotensive, had elevated jugular venous pressure and clear lungs. ECG revealed atrial fibrillation with the rapid ventricular rate. Labs were significant for markedly elevated pro-brain natriuretic peptide of 43,000 pg/mL and troponin-T of 1 ng/mL. An urgent 2D echocardiogram was obtained, which revealed the severely dilated right atrium and a large linear mobile mass in the right atrium consistent with a thrombus. An emergent CT scan revealed multiple bilateral pulmonary emboli. She received intravenous tissue plasminogen activator. Repeat echocardiogram performed 6 h later showed no evidence of the right atrial thrombus. She was subsequently maintained on intravenous heparin and transitioned to Coumadin. Early recognition of this rare but potentially fatal complication is important as prompt treatment measures can help in preventing life-threatening complications of the right atrial thrombus.

Dynamics of survival of motor neuron (SMN) protein interaction with the mRNA-binding protein IMP1 facilitates its trafficking into motor neuron axons

Thu, 01/15/2015 - 2:42pm

Spinal muscular atrophy (SMA) is a lethal neurodegenerative disease specifically affecting spinal motor neurons. SMA is caused by the homozygous deletion or mutation of the survival of motor neuron 1 (SMN1) gene. The SMN protein plays an essential role in the assembly of spliceosomal ribonucleoproteins. However, it is still unclear how low levels of the ubiquitously expressed SMN protein lead to the selective degeneration of motor neurons. An additional role for SMN in the regulation of the axonal transport of mRNA-binding proteins (mRBPs) and their target mRNAs has been proposed. Indeed, several mRBPs have been shown to interact with SMN, and the axonal levels of few mRNAs, such as the beta-actin mRNA, are reduced in SMA motor neurons. In this study we have identified the beta-actin mRNA-binding protein IMP1/ZBP1 as a novel SMN-interacting protein. Using a combination of biochemical assays and quantitative imaging techniques in primary motor neurons, we show that IMP1 associates with SMN in individual granules that are actively transported in motor neuron axons. Furthermore, we demonstrate that IMP1 axonal localization depends on SMN levels, and that SMN deficiency in SMA motor neurons leads to a dramatic reduction of IMP1 protein levels. In contrast, no difference in IMP1 protein levels was detected in whole brain lysates from SMA mice, further suggesting neuron specific roles of SMN in IMP1 expression and localization. Taken together, our data support a role for SMN in the regulation of mRNA localization and axonal transport through its interaction with mRBPs such as IMP1.

Pediatric head injury and concussion

Thu, 01/15/2015 - 2:42pm

Children with head injuries frequently present to emergency departments. Even though most of these children have minor injuries, head injury is the most common cause of traumatic deaths in pediatric patients. The pediatric GCS and decision rules for obtaining head CT imaging help the provider evaluate head-injured infants and children. The provider must be vigilant to diagnose those who have life-threatening intracranial injuries or are victims of abusive head trauma. The goal of the emergency physician is to diagnose and treat the consequences of the primary injury and to limit or prevent secondary injury.

The Legionella pneumophila GTPase activating protein LepB accelerates Rab1 deactivation by a non-canonical hydrolytic mechanism

Thu, 01/15/2015 - 2:42pm

GTPase activating proteins (GAPs) from pathogenic bacteria and eukaryotic host organisms deactivate Rab GTPases by supplying catalytic arginine and glutamine fingers in trans and utilizing the cis-glutamine in the DXXGQ motif of the GTPase for binding rather than catalysis. Here, we report the transition state mimetic structure of the Legionella pneumophila GAP LepB in complex with Rab1 and describe a comprehensive structure-based mutational analysis of potential catalytic and recognition determinants. The results demonstrate that LepB does not simply mimic other GAPs but instead deploys an expected arginine finger in conjunction with a novel glutamic acid finger, which forms a salt bridge with an indispensible switch II arginine that effectively locks the cis-glutamine in the DXXGQ motif of Rab1 in a catalytically competent though unprecedented transition state configuration. Surprisingly, a heretofore universal transition state interaction with the cis-glutamine is supplanted by an elaborate polar network involving critical P-loop and switch I serines. LepB further employs an unusual tandem domain architecture to clamp a switch I tyrosine in an open conformation that facilitates access of the arginine finger to the hydrolytic site. Intriguingly, the critical P-loop serine corresponds to an oncogenic substitution in Ras and replaces a conserved glycine essential for the canonical transition state stereochemistry. In addition to expanding GTP hydrolytic paradigms, these observations reveal the unconventional dual finger and non-canonical catalytic network mechanisms of Rab GAPs as necessary alternative solutions to a major impediment imposed by substitution of the conserved P-loop glycine.

Using stable MutS dimers and tetramers to quantitatively analyze DNA mismatch recognition and sliding clamp formation

Thu, 01/15/2015 - 2:42pm

The process of DNA mismatch repair is initiated when MutS recognizes mismatched DNA bases and starts the repair cascade. The Escherichia coli MutS protein exists in an equilibrium between dimers and tetramers, which has compromised biophysical analysis. To uncouple these states, we have generated stable dimers and tetramers, respectively. These proteins allowed kinetic analysis of DNA recognition and structural analysis of the full-length protein by X-ray crystallography and small angle X-ray scattering. Our structural data reveal that the tetramerization domains are flexible with respect to the body of the protein, resulting in mostly extended structures. Tetrameric MutS has a slow dissociation from DNA, which can be due to occasional bending over and binding DNA in its two binding sites. In contrast, the dimer dissociation is faster, primarily dependent on a combination of the type of mismatch and the flanking sequence. In the presence of ATP, we could distinguish two kinetic groups: DNA sequences where MutS forms sliding clamps and those where sliding clamps are not formed efficiently. Interestingly, this inability to undergo a conformational change rather than mismatch affinity is correlated with mismatch repair.