Prognostic value of coronary multidetector CT angiography in patients with an intermediate probability of significant coronary heart disease

The aim of this study was to determine the prognostic value of coronary multidetector CT angiography (MDCTA) in patients with an intermediate pre-test probability of significant coronary artery disease (CAD). Patients who underwent 64-slice coronary MDCTA and met the selection criteria were identified and assessed for intermediate pre-test probability. Coronary MDCTA scans were preceded by calcium scoring, whereas all MDCTA scans were interrogated for the presence of plaque composition and the distribution and degree of stenosis. Significant stenosis was classified as being >50% of the luminal diameter. All patients were followed up for the occurrence of (i) cardiac death, (ii) non-fatal myocardial infarction, (iii) unstable angina requiring hospital admission and (iv) revascularisation. 138 patients were included (follow-up of 19.9 months); of these, 8 had a cardiac event (all revascularisations) and all had a positive coronary MDCTA. Patients with normal coronary arteries or non-significant stenosis suffered no cardiac events during follow-up. There were significant differences between the two groups regarding the presence of significant stenosis (p<0.001), the presence of plaque (p = 0.011) and a calcium score >10 (p = 0.003); 36.4% of patients with significant stenosis underwent revascularisation. In conclusion, this is the first UK study to investigate survival data in a population of intermediate-risk patients with no prior history of CAD who were investigated with coronary MDCTA. Coronary MDCTA can confidently rule out significant CAD in the intermediate-risk population and guide risk factor modification in patients with demonstrated coronary atheroma.

Structure of Cry2Aa suggests an unexpected receptor binding epitope

BACKGROUND

Genetically modified (GM) crops that express insecticidal protein toxins are an integral part of modern agriculture. Proteins produced by Bacillus thuringiensis (Bt) during sporulation mediate the pathogenicity of Bt toward a spectrum of insect larvae whose breadth depends upon the Bt strain. These transmembrane channel-forming toxins are stored in Bt as crystalline inclusions called Cry proteins. These proteins are the active agents used in the majority of biorational pesticides and insect-resistant transgenic crops. Though Bt toxins are promising as a crop protection alternative and are ecologically friendlier than synthetic organic pesticides, resistance to Bt toxins by insects is recognized as a potential limitation to their application.

RESULTS

We have determined the 2.2 A crystal structure of the Cry2Aa protoxin by multiple isomorphous replacement. This is the first crystal structure of a Cry toxin specific to Diptera (mosquitoes and flies) and the first structure of a Cry toxin with high activity against larvae from two insect orders, Lepidoptera (moths and butterflies) and Diptera. Cry2Aa also provides the first structure of the proregion of a Cry toxin that is cleaved to generate the membrane-active toxin in the larval gut.

CONCLUSIONS

The crystal structure of Cry2Aa reported here, together with chimeric-scanning and domain-swapping mutagenesis, defines the putative receptor binding epitope on the toxin and so may allow for alteration of specificity to combat resistance or to minimize collateral effects on nontarget species. The putative receptor binding epitope of Cry2Aa identified in this study differs from that inferred from previous structural studies of other Cry toxins.

Energetic contributions of four arginines to phosphate-binding in thymidylate synthase are more than additive and depend on optimization of "effective charge balance"

In thymidylate synthase, four conserved arginines provide two hydrogen bonds each to the oxygens of the phosphate group of the substrate, 2'-deoxyuridine-5'-monophosphate. Of these, R23, R178, and R179 are far removed from the site of methyl transfer and contribute to catalysis solely through binding and orientation of ligands. These arginines can be substituted by other residues, while still retaining more than 1% activity of the wild-type enzyme. We compared the kinetics and determined the crystal structures of dUMP complexes of three of the most active, uncharged single mutants of these arginines, R23I, R178T, and R179T, and of double mutants (R23I, R179T) and (R178T, R179T). The dramatically higher K(m) for R178T compared to the other two single mutants arises from the effects of R178 substitution on the orientation of dUMP; 10-15-fold increases in for R23I and R178T reflect the role of these residues in stabilizing the closed conformation of TS in ternary complexes. The free energy for productive dUMP binding, DeltaG(S), increases by at least 1 kcal/mol for each mutant, even when dUMP orientation and mobility in the crystal structure is the same as in wild-type enzyme. Thus, the four arginines do not contribute excess positive charge to the PO(4)(-2) binding site; rather, they ideally complement the charge and geometry of the phosphate moiety. More-than-additive increases in DeltaG(S) seen in the double mutants are consistent with quadratic increases in DeltaG(S) predicted for deviations from ideal electrostatic interactions and may also reflect cooperative binding of the arginines to the phosphate oxygens.

Contribution of a salt bridge to binding affinity and dUMP orientation to catalytic rate: mutation of a substrate-binding arginine in thymidylate synthase

Invariant arginine 179, one of four arginines that are conserved in all thymidylate synthases (TS) and that bind the phosphate moiety of the substrate 2'-deoxyuridine-5'-monophosphate (dUMP), can be altered even to a negatively charged glutamic acid with little effect on kcat. In the mutant structures, ordered water or the other phosphate-binding arginines compensate for the hydrogen bonds made by Arg179 in the wild-type enzyme and there is almost no change in the conformation or binding site of dUMP. Correlation of dUMP Kds for TS R179A and TS R179K with the structures of their binary complexes shows, that the positive charge on Arg179 contributes significantly to dUMP binding affinity. kcat/K(m) for dUMP measures the rate of dUMP binding to TS during the ordered bi-substrate reaction, and in the ternary complex dUMP provides a binding surface for the cofactor. kcat/K(m) reflects the ability of the enzyme to accept a properly oriented dUMP for catalysis and is less sensitive than is Kd to the changes in electrostatics at the phosphate binding site.

Alcohol use among black youths in a rural community

The results of this study lead to the conclusion that the circumstances which surround the act of youth drinking in the black population of an abstinence setting are somewhat different from those recorded elsewhere. Although fewer students drink, the drinking styles reveal several dimensions frequently associated with alcohol abuse. As a rule, users do not have parental permission to drink and for the most part they identify with churches that condemn alcohol on moral grounds. Because many of the youth procure their beverages from illegal sources or in an illegal way, they tend to drink in a surreptitious manner in a setting absent of restraint. Consequently, a significant number of youths were drinking without normal propriety and were exhibiting several social complications as a result. This suggests that less drinking can be expected in abstinence settings but, among those young people who drink, problems may be more frequent. This is logical since the user is at variance with the normative prescriptions of the community, church and home. Obviously, drinking under these conditions may actually be an expression of a general test of the limits of the adult world or a symbol of rejection of adult standards. Subsequently, the abuse of alcohol may decrease with maturity. Regardless of their meaning, however, the findings do point to a need for education about alcohol at the school level.