ECG interpretation skill acquisition: A review of learning, teaching and assessment

The recording of 12 lead electrocardiograms (ECG) is one of the most useful and commonly performed medical procedures. ECGs are used in diagnosis, risk-stratification management decision-making, and assessment in response to therapy. The correct interpretation of 12 lead ECG recordings is complex and clinically challenging with misinterpretation having the potential to result in poor outcomes or even patient fatality. Despite its widespread use, several studies have highlighted deficiencies in ECG interpretation skills among health professionals. The literature suggests that up to 33% of ECG interpretations have some error when compared to the expert reference and up to 11% resulted in inappropriate management. The pedagogy of ECG interpretation lacks universal establishment; time allocation, faculty training and teaching format vary considerably within the literature. This review of the literature reports how a lack of established ECG reporting methods may contribute to the variation in reported ECG interpretation competence across many healthcare professionals. The ubiquity of the ECG in clinical practice and an over reliance on computer assisted ECG interpretation are additionally explored as factors affecting acquisition and retention of this clinical skill.

Allosteric regulation of deubiquitylase activity through ubiquitination

Ataxin-3, the protein responsible for spinocerebellar ataxia type-3, is a cysteine protease that specifically cleaves poly-ubiquitin chains and participates in the ubiquitin proteasome pathway. The enzymatic activity resides in the N-terminal Josephin domain. An unusual feature of ataxin-3 is its low enzymatic activity especially for mono-ubiquitinated substrates and short ubiquitin chains. However, specific ubiquitination at lysine 117 in the Josephin domain activates ataxin-3 through an unknown mechanism. Here, we investigate the effects of K117 ubiquitination on the structure and enzymatic activity of the protein. We show that covalently linked ubiquitin rests on the Josephin domain, forming a compact globular moiety and occupying a ubiquitin binding site previously thought to be essential for substrate recognition. In doing so, ubiquitination enhances enzymatic activity by locking the enzyme in an activated state. Our results indicate that ubiquitin functions both as a substrate and as an allosteric regulatory factor. We provide a novel example in which a conformational switch controls the activity of an enzyme that mediates deubiquitination.

Enzymatic production of mono-ubiquitinated proteins for structural studies: The example of the Josephin domain of ataxin-3

Protein ubiquitination occurs through formation of an isopeptide bond between the C-terminal glycine of ubiquitin (Ub) and the ɛ-amino group of a substrate lysine residue. This post-translational modification, which occurs through the attachment of single and/or multiple copies of mono-ubiquitin and poly-ubiquitin chains, is involved in crucial cellular events such as protein degradation, cell-cycle regulation and DNA repair. The abnormal functioning of ubiquitin pathways is also implicated in the pathogenesis of several human diseases ranging from cancer to neurodegeneration. However, despite the undoubted biological importance, understanding the molecular basis of how ubiquitination regulates different pathways has up to now been strongly limited by the difficulty of producing the amounts of highly homogeneous samples that are needed for a structural characterization by X-ray crystallography and/or NMR. Here, we report on the production of milligrams of highly pure Josephin mono-ubiquitinated on lysine 117 through large scale in vitro enzymatic ubiquitination. Josephin is the catalytic domain of ataxin-3, a protein responsible for spinocerebellar ataxia type 3. Ataxin-3 is the first deubiquitinating enzyme (DUB) reported to be activated by mono-ubiquitination. We demonstrate that the samples produced with the described method are correctly folded and suitable for structural studies. The protocol allows facile selective labelling of the components. Our results provide an important proof-of-concept that may pave the way to new approaches to the in vitro study of ubiquitinated proteins.

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We set up a protocol for large-scale in vitro enzymatic ubiqitination.

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This produced milligrams of highly pure mono-ubiquitinated Josephin domain of ataxin-3.

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We applied an alternative labelling scheme for the structural characterization of the sample by NMR.

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Ubiquitin covalently linked on lysine 117 directly interacts with Josephin but does not alter the overall fold of the protein.

Solution structure, hydrodynamics and thermodynamics of the UvrB C-terminal domain

The solution structure, thermodynamic stability and hydrodynamic properties of the 55-residue C-terminal domain of UvrB that interacts with UvrC during excision repair in E. coli have been determined using a combination of high resolution NMR, ultracentrifugation, 15N NMR relaxation, gel permeation, NMR diffusion, circular dichroism and differential scanning calorimetry. The subunit molecular weight is 7,438 kDa., compared with 14.5+/-1.0 kDa. determined by equilibrium sedimentation, indicating a dimeric structure. The structure determined from NMR showed a stable dimer of anti-parallel helical hairpins that associate in an unusual manner, with a small and hydrophobic interface. The Stokes radius of the protein decreases from a high plateau value (ca. 22 A) at protein concentrations greater than 4 microM to about 18 A at concentrations less than 0.1 microM. The concentration and temperature-dependence of the far UV circular dichroism show that the protein is thermally stable (Tm ca. 71.5 degrees C at 36 microM). The simplest model consistent with these data was a dimer dissociating into folded monomers that then unfolds co-operatively. The van't Hoff enthalpy and dissociation constant for both transition was derived by fitting, with deltaH1=23 kJ mol(-1). K1(298)=0.4 microM and deltaH2= 184 kJ mol(-1). This is in good agreement with direct calorimetric analysis of the thermal unfolding of the protein, which gave a calorimetric enthalpy change of 181 kJ mol(-1) and a van't Hoff enthalpy change of 354 kJ mol(-1), confirming the dimer to monomer unfolding. The thermodynamic data can be reconciled with the observed mode of dimerisation. 15N NMR relaxation measurements at 14.1 T and 11.75 T confirmed that the protein behaves as an asymmetric dimer at mM concentrations, with a flexible N-terminal linker for attachment to the remainder of the UvrB protein. The role of dimerisation of this domain in the excision repair mechanism is discussed.

Analysis of backbone dynamics in cytochrome b5 using 15N-NMR relaxation measurements

Determination of 15N-NMR relaxation rates has allowed the characterisation of the dynamic properties of 55 1H-15N bond vectors in a soluble haem-binding domain of bovine microsomal ferricytochrome b5 consisting of the first 104 amino acid residues. Measurements of heteronuclear [1H]-15N-NMR nuclear Overhauser effects, and 15N-NMR longitudinal and transverse relaxation rates have been analysed using both model-free and reduced spectral density mapping approaches, demonstrating the application of these methods to a paramagnetic system. Analysis reveals that, for those regions which have been assessed, the polypeptide backbone of ferricytochrome b5 is largely rigid (average S2 = 0.80), and that minimal internal backbone motion occurs on the sub-nanosecond timescale. In contrast, motions on the microsecond to millisecond timescale, especially pronounced for the loop region extending from residues 28 to 31, and which may be of biological relevance, are indicated.

The solution structure of bovine ferricytochrome b5 determined using heteronuclear NMR methods

The solution structure of a recombinant form of cytochrome b5 containing 104 amino acid residues has been determined using three-dimensional NMR spectroscopy. Using protein enriched in 15N the majority of the polypeptide backbone resonances have been assigned to reveal numerous chemical shift differences to those reported previously for smaller fragments of cytochrome b5. By using 3D NMR methods the extensive spectral overlap of resonance cross-peaks in 2D NMR spectra could be satisfactorily resolved. The large number of sequence-specific assignments made for this form of the protein allowed the identification of over 1130 NOEs, giving an average of 14 NOEs per assigned residue, and 52 dihedral angles (phi). This data was used in an ab initio simulated annealing protocol to determine the solution structure for bovine microsomal cytochrome b5. A series of 50 structures was generated using distance restraints derived from the magnitude of the NOE and torsional angles based on the measured JHN-HA coupling constants. From an initial round of simulated annealing a family of 36 structures was selected on the basis of good covalent geometry and minimal restraint violations. A single cycle of simulated annealing refinement produced 36 converged structures that exhibited an average r.m.s.d. of 0.73 A for the backbone atoms. The determination of the solution structure of cytochrome b5 is the first using NMR methods for any form of this protein. It is also the only cytochrome whose structure has been determined in the oxidised or paramagnetic state. The results show that despite significant line broadening and pseudocontact shifts for resonances lying close to the paramagnetic haem centre, and despite extensive spectral overlap that prevents complete resonance assignment, the topology of the polypeptide backbone can be derived. The conformation for cytochrome b5 determined in this study reveals several small, but significant, differences in structure to that determined previously by crystallography for a smaller fragment of this protein. For example, NMR data do not support a short beta strand as the first element of secondary structure at the N terminus nor is it likely that a beta-bulge structure forms between residues 75 to 79. The data obtained in this study are more consistent with a turn in this region of the protein linking helices 5 and 6 and leads to cytochrome b5 containing only three clearly defined beta strands. Four of the six helices together with the antiparallel beta strands make up a haem binding pocket in which the solvent-accessible area of the protoporphyrin IX centre remains very similar to that found in the crystal structure. The remaining helices and the beta strands form a second structural domain on which the four helix bundle that surrounds the haem is based. THe derivation of the solution structure of cytochrome b5 will allow a greater understanding of the functional properties of cytochrome b5 including its role in biological electron transfer and molecular recognition together with insight into haem protein folding and stability.

Extraction of Light Filth from Oriental Sauces Containing Soy Sauce, Thickeners, and Spices: Collaborative Study

Results are reported for a collaborative study of a method for the extraction of light filth from oriental sauces containing soy sauce, thickeners, and spices. A100 g test portion is pretreated in a 2% solution of Tergitol Anionic 4 over a steam bath, and oils are removed by wet-sieving on No. 230 sieve. Filth is isolated from 40% isopropanol by using Na4EDTA and mineral oil. Average recoveries by 9 collaborators for 3 spike levels of rat hairs (5,10, and 15) were 84, 78, and 79%, respectively; for insect fragments (5,15, and 30), recoveries were 92, 95, and 96%, respectively. The method was adopted first action by AOAC International.

Radiographs in clinical periodontal trials

Fifty-eight patients were selected from an ongoing study of periodontal therapy at The University of Michigan. Pre-and post-treatment series of full mouth radiographs obtained by conventional paralleling long cone technique were available. Mesial and distal radiographic bone height was scored using the technique developed by Björn et al. A total of 1416 teeth were scored from the itial radiographs, and subsequently at one, two, three, and four years after the treatment. Radiographic bone height scores were compared with level of attachment and pocket depth scores for the same teeth at the same time. Statistical significance and correlation coefficients were derived using computer analysis of the data. The data were analyzed using three different data groupings: individual teeth, patient means, and half-mouth treatment methods. High positive correlations were found between initial measurements of radiographic bone height and attachment level as well as pocket depth. The correlations between changes in measurements of radiographic bone height and attachment level after treatment were markedly lower but are statistically significant. A highly significant correlation between radiographic bone heights and measurements of attachment level also appeared in follow-up data one to four years after treatment. The method of data grouping resulted in different correlation coefficients. Highest correlations were found if the data were pooled for patients. Lowest correlations were found if the data for individual teeth were analyzed. When the data were combined to produce patient scores, sample variation is reduced and correlations increase in magnitude. The generally high correlations between radiographic bone height and attachment level scores before and after treatment tend to confirm the fact that radiographic assessment of alveolar bone height using the method of Björn et al. can provide fairly accurate assessment of interproximal periodontal support.