Structure and dynamics of the full-length lipid-modified H-Ras protein in a 1,2-dimyristoylglycero-3-phosphocholine bilayer

Ras proteins regulate signal transduction processes that control cell growth and proliferation. Their disregulation is a common cause of human tumors. Atomic level structural and dynamical information in a membrane environment is crucial for understanding signaling specificity among Ras isoforms and for the design of selective anti-cancer agents. Here, the structure of the full-length H-Ras protein in complex with a 1,2-dimyristoylglycero-3-phosphocholine (DMPC) bilayer obtained from modeling and all-atom explicit solvent molecular dynamics simulations, as well as experimental validation of the main results, are presented. We find that, in addition to the lipid anchor, H-Ras membrane binding involves direct interaction of residues in the catalytic domain with DMPC phosphates. Two modes of binding (possibly modulated by GTP/GDP exchange) differing in the orientation and bilayer contact of the soluble domain as well as in the participation of the flexible linker in membrane binding are proposed. These results are supported by our initial in vivo experiments. The overall structures of the protein and the bilayer remain similar to those of the isolated components, with few localized structural and dynamical changes. The implications of the results to membrane lateral segregation and other aspects of Ras signaling are discussed.     

Hypocupremia associated cytopenia and myelopathy: a national retrospective review

Copper is an essential trace element that is involved in a number of important enzymatic processes throughout the body. Recent single case reports and small studies have shown that deficiency of copper can cause reversible haematological changes and irreversible neurological injury. We chose to undertake a national study, looking at all cases of copper deficiency in Scotland over a 5‐yr period using information from a national reference laboratory. From 16 identified patients, we determined that 86% had both haematological and neurological features of copper deficiency, while 18% had haematological features only at presentation. Twelve of the sixteen patients had high serum zinc concentrations (>18 μm/L) nine patients were using zinc‐containing dental fixatives at time of diagnosis. 94% of patients had haematological features as an initial manifestation of copper deficiency, which included anaemia, thrombocytopenia and neutropenia. Patients who underwent later bone marrow testing had appearances in keeping with refractory cytopenia with multilineage dysplasia, refractory anaemia with excess of blasts, unclassified marrow dysplasia or probable myelodysplasia (MDS). 75% of patients had neurological symptoms or signs, including progressive walking difficulties and paraesthesia, or gait difficulties without sensory signs. Clinical examination was in keeping with spastic paraparesis (either with or without sensory neuropathy). Magnetic resonance imaging (MRI) showed multifocal T2 hyper intense foci in the subcortical white matter, and atrophy of the cerebrum and cerebellum was also seen on computerised tomography (CT). MRI of the spinal cord showed signal change in the dorsal columns in either the cervical or thoracic cord. 93% of cytopenias responded to copper replacement and addressing the original cause of the copper deficiency, but only 25% of patients had improvement in their neurological function, while 33% deteriorated and 42% remained unchanged. Our study demonstrates that copper deficiency is an under‐recognised cause of several types of cytopenia, which are reversible but can progress to significant neurological injury if left untreated. We illustrate the importance of identifying these patients early to prevent irreversible neurological injury.     

A new paradigm for deriving and analyzing number needed to treat

The inverse of the risk difference, commonly referred to as the number needed to treat (NNT) has been recently proposed as a useful measure for comparing two treatments. Since its introduction, the method has been used widely to establish comparative treatment benefits, and has also been the subject of extensive discussions among statisticians. In this paper, we examine the assumptions behind the original definition of NNT, and introduce a new formulation of the method based on a random walk model. Using stopping times, we develop a paradigm for NNT that avoids some of the conceptual and inferential difficulties and pitfalls associated with the previous work on NNT. Simulation results are provided to illustrate the bias introduced by using alternative formulations of NNT, and several open problems are suggested for future research.     

The association between epilation and corneal opacity among eyes with trachomatous trichiasis

AIM: To examine the association between epilation and corneal opacity (CO) among trichiasis patients presenting for surgery. METHODS: Cross sectional data from the STAR trial were utilised. Patients presenting for trichiasis surgery in Wolayta Zone, Ethiopia, were evaluated for current trichiasis status. Number of inturned lashes, evidence of epilation, level of entropion, trichiasis duration, and CO were collected. The primary outcome was prevalence of CO, stratified by entropion and epilation status. RESULTS: Approximately 10% of eyes with mild entropion had CO, regardless of epilation status. Among eyes with moderate entropion, epilated eyes were less likely to have CO than non-epilated eyes (21% v 34% p = 0.002). The same association was seen in eyes with severe entropion: 43% of epilated eyes while 74% of non-epilated eyes had CO (p<0.0001). Presence of CO increased with age. Adjusted models showed a protective effect of epilation in eyes with moderate or severe entropion (OR: 0.51; 95% CI: 0.32 to 0.83 and OR: 0.24; 95% CI: 0.13 to 0.45, respectively). Among eyes with mild entropion there was no difference in the prevalence of CO comparing eyes that were epilated with those that were not epilated. CONCLUSION: Entropion was the most significant predictor of CO. Cross sectional associations suggest that epilation may not be helpful for eyes with mild entropion, but may offer protection against CO in eyes with moderate to severe entropion. Epilation should not be a substitute for trichiasis surgery, however, as 43% of eyes with severe entropion that were epilated still had CO.     

Trichiasis among close relatives, central Ethiopia

Active trachoma is known to cluster in close contacts, such as mother and child and between siblings, but we do not know the pattern for trichiasis. This cross-sectional study was conducted to determine if there is as much trichiasis as active trachoma within families having close contact. This information will be helpful in designing intervention strategies. Trichiasis patients that presented for surgery were interviewed for the presence or absence of trichiasis in the current nuclear family, their parent/s, brother/s, sister/s, aunt/s or uncle/s. Of the 739 trichiasis patients interviewed, 78% were women. Fourteen percent of trichiasis cases had at least one nuclear family member with the same condition, and 20.0% had other relative/s (parent/s, brother/ s, sister/s, aunt/s or uncle/s) with trichiasis. Trichiasis increases in parallel with the increase in family size of the index case (c2 for trend = 70.6; P < 0.001). Sixty-nine percent of affected nuclear family members of the index cases were female members. In the relative with trichiasis, 92.8% of cases were parents, sisters and brothers of the index cases. Out of these, the majority (70%) were mothers and sisters. The chance of a female trichiasis patient having another relative with trichiasis is 70%. The chance of the mother/sister/s of a male trichiasis patient being trichiasis patients themselves is 80%, while that of the father/brother/s is 20% (c2=21.88; P < 0.001). If a female has trichiasis there is a 70% chance of her mother/sister/s, and 30% chance of the father/ brother/s (c2 = 27.52; P <0.001) also being trichiasis patients.     

The new middle level health workers training in the Amhara regional state of Ethiopia: students' perspective

Background  

Following health sector reform, Ethiopia started training new categories of health workers. This study addresses students' perspectives regarding their training and career plans.     

Clinical features of gastroduodenal Crohn's disease in adolescents

Ten cases of gastroduodenal inflammation were diagnosed by endoscopy among a series of 196 children with evidence of Crohn's disease involving other regions of the intestinal tract. Endoscopic and histologic confirmation of upper gastrointestinal tract involvement was performed only in those cases with suggestive symptoms. The mean age at presentation in the 10 cases with gastroduodenal inflammation was 14.6 +/- 1.9 (+/- SD) years, with involvement identified at the time of initial diagnosis of Crohn's disease in five of the 10. Eight of 10 cases occurred in boys. The major presenting symptoms were weight loss in five cases, epigastric pain in three, and recurrent vomiting in two. Hematemesis and melena occurred in only one of the 10 cases. Endoscopic and histological evidence of mucosal inflammation was seen in all 10 cases. Three of 10 cases had noncaseating granuloma present in biopsies of the stomach or duodenum. Two cases also had endoscopic and histological evidence of esophageal involvement. All cases were initially treated with oral corticosteroids, and in each instance a good clinical response was noted. Sucralfate (n = 1), 6-mercaptopurine (n = 1), and H2 receptor antagonists (n = 3) were used as adjunct therapy. After follow-up for 2.7 years (range, 0.5-5.5 years), none of the 10 cases required surgical intervention. Therefore, at least in the short-term, the outlook for adolescents with gastroduodenal Crohn's disease appears to be good and their medical management need not differ from those patients with Crohn's disease involving only more distal portions of the small intestine.     

X-ray absorption spectroscopy of exemplary platinum porphyrin and corrole derivatives: metal- versus ligand-centered oxidation

A combination of Pt L₃-edge X-ray absorption spectroscopy (EXAFS and XANES) and DFT (TPSS) calculations have been performed on powder samples of the archetypal platinum porphyrinoid complexes Pt^II[TpCF₃PP], Pt^IV[TpCF₃PP]Cl₂, and Pt^IV[TpCF₃PC](Ar)(py), where TpCF₃PP²⁻ = meso-tetrakis(p-trifluoromethylphenyl)porphyrinato and TpCF₃PC³⁻ = meso-tris(p-trifluoromethylphenyl)corrolato. The three complexes yielded Pt L₃-edge energies of 11 566.0 eV, 11 567.2 eV, and 11 567.6 eV, respectively. The 1.2 eV blueshift from the Pt(ii) to the Pt(iv) porphyrin derivative is smaller than expected for a formal two-electron oxidation of the metal center. A rationale was provided by DFT-based Hirshfeld which showed that the porphyrin ligand in the Pt(iv) complex is actually substantially oxidized relative to that in the Pt(ii) complex. The much smaller blueshift of 0.4 eV, going from Pt^IV[TpCF₃PP]Cl₂, and Pt^IV[TpCF₃PC](Ar)(py), is ascribable to the significantly stronger ligand field in the latter compound.

Platinum L₃-edge XAS and DFT calculations on three well-characterized Pt porphyrinoid complexes have provided detailed insights into metal- versus ligand-centered oxidation and ligand field effects.     

Regioselective formylation of rhenium-oxo and gold corroles: substituent effects on optical spectra and redox potentials

Vilsmeier–Haack formylation of ReO and Au meso-triarylcorroles over 16–18 hours affords moderate to good yields (47–65%) of the ReO-3-formyl and Au-3,17-diformyl derivatives in a highly regioselective manner. Formylation was found to effect substantial upshifts for redox potentials (especially the reduction potentials) as well as significant to dramatic redshifts for both the Soret and Q bands.

Vilsmeier–Haack formylation of ReO and Au meso-triarylcorroles over 16–18 hours affords moderate to good yields (47–65%) of the ReO-3-formyl and Au-3,17-diformyl derivatives in a highly regioselective manner.