Biomedical subjects

E Christodoulou

Publications and source records attributed to E Christodoulou.

7 recordsLinked to original sources

PubMed2006

Implementation of semi-automated cloning and prokaryotic expression screening: the impact of SPINE.

The implementation of high-throughput (HTP) cloning and expression screening in Escherichia coli by 14 laboratories in the Structural Proteomics In Europe (SPINE) consortium is described. Cloning efficiencies of greater than 80% have been achieved for the three non-ligation-based cloning techniques used, namely Gateway, ligation-indendent cloning of PCR products (LIC-PCR) and In-Fusion, with LIC-PCR emerging as the most cost-effective. On average, two constructs have been made for each of the approximately 1700 protein targets selected by SPINE for protein production. Overall, HTP expression screening in E. coli has yielded 32% soluble constructs, with at least one for 70% of the targets. In addition to the implementation of HTP cloning and expression screening, the development of two novel technologies is described, namely library-based screening for soluble constructs and parallel small-scale high-density fermentation.

Amino Acid Sequence↗

PubMed2006

Virtual bronchoscopy versus thin section computed tomography in evaluation of moderate and low grade stenoses: receiver operating characteristic curve analysis.

PURPOSE: To evaluate the impact of virtual bronchoscopy, under proper threshold settings, on observer level of confidence in the assessment of bronchial abnormalities producing stenoses < or = 75% compared to interpretation of thin section computed tomography (CT) images. MATERIAL AND METHODS: Sixty-five patients with fiberoptic bronchoscopy positive for tracheobronchial abnormalities were evaluated in a blinded observer study using a commercially available virtual endoscopy software package. The findings of virtual endoscopy were compared with those of fiberoptic bronchoscopy using receiver operating characteristic curves (ROCs) and other statistical tools. RESULTS: A total of 102 lesions were identified by fiberoptic bronchoscopy, with 44 of these producing bronchial stenoses < or = 75%. Concerning the latter lesions, for virtual bronchoscopy the areas under the ROCs were 0.93 and 0.96 for the two observers, respectively, while for thin section CT the corresponding values were 0.86 and 0.88; the differences observed were statistically significant. Contrary to thin section CT, virtual bronchoscopy did not show statistically significant differences from fiberoptic bronchoscopy regarding estimation of degree of stenosis. CONCLUSION: Virtual bronchoscopy under proper threshold settings has a statistically significant impact on observer performance where moderate and low-grade bronchial stenoses are concerned and gives an estimate of the degree of stenosis more precisely than thin section CT.

Adult↗

PubMed2001

Overexpression, purification, and characterization of a thermostable chitinase (Chi40) from Streptomyces thermoviolaceus OPC-520.

A new procedure for the large-scale purification of the recombinant thermostable chitinase (Chi40) cloned from Streptomyces thermoviolaceus in various expression vectors in Escherichia coli is described. Chi40 was overproduced in the cytosolic and secreted forms. The cytosolic form (Chi40c) was highly overproduced and purified by metal-affinity and ion-exchange chromatography in large amounts. The protein was highly active and thermostable but not homogeneous, since a considerable proportion of the Chi40c protein was not correctly folded as determined by native polyacrylamide gel electrophoresis. The Chi40 protein secreted into the culture medium (Chi40s) was purified by hydrophobic interaction and ion-exchange chromatography and high amounts of correctly folded and active Chi40 protein could be recovered in a short time. The enzymatic activity of Chi40s on a synthetic and on its natural substrate, chitin, was studied. Thermostability measurements showed that Chi40 has a T(m) of 60.7 degrees C at neutral pH. (13)C-(15)N double-labeled recombinant Chi40s was also produced and purified from the pECHChi40-9 construct introduced into BL21trxB(DE3) cells grown in minimal medium in the presence of the paramagnetic elements [(13)C]glucose and (15)NH(4)Cl. The presented data open the possibility of an extensive structural study on Chi40s by X-ray crystallography and on enzyme-substrate interaction by NMR spectroscopy.

Carbon Isotopes↗

PubMed1999

Design and evaluation of an external filter technique for exposure equalization in mammography.

We are developing an external filter method for equalizing x-ray exposure in the peripheral region of the breast. This method requires the use of only a limited number of custom-built filters for different breast shapes in a given view. This paper describes the design methodology for these external filters. The filter effectiveness was evaluated through a simulation study on 171 mediolateral and 196 craniocaudal view digitized mammograms and through imaging of a breast phantom. The degree of match between the simulated filter and the individual 3-D exposure profiles at the breast periphery was quantified. An analysis was performed to investigate the effect of filter misalignment. The simulation study indicates that the filter is effective in equalizing exposures for more than 80% of the breast images in our database. The tolerance in filter misalignment was estimated to be about +/- 2 mm for the CC view and +/- 1 mm for the MLO view at the image plane. Some misalignment artifacts were demonstrated with simulated filtered mammograms.

Biophysical Phenomena↗

PubMed1998

Cloning, overproduction, purification and crystallization of the DNA binding protein HU from the hyperthermophilic eubacterium Thermotoga maritima.

The humar gene encoding for the histone-like DNA-binding protein HU from the hyperthermophilic eubacterium Thermotoga maritima was efficiently overexpressed in Escherichia coli under the T7 promoter. The HU protein was purified using SP-Sepharose ion-exchange and heparin-affinity chromatography and was successfully crystallized in ammonium sulfate. The crystals were grown in the tetragonal form in space group P43 or P41 and have unit-cell dimensions a = b = 46.12, c = 77.56 A, alpha = beta = gamma = 90 degrees. The crystals diffract X-rays to 1.6 A resolution using synchrotron radiation and are suitable for determination of the HU structure at high resolution.

Bacteria↗

PubMed1991

Broad beam transmission properties of some common shielding materials for use in diagnostic radiology.

Broad beam geometry was used to measure the x-ray transmission properties of gypsum wallboard, steel, plate glass, and concrete for x-ray tube potentials of 50-125 kVp using an x-ray generator having a three-phase, twelve-pulse waveform and total initial beam filtration sufficient to provide half-value layers representative of those found in common practice and required by regulatory agencies. Measurement results are presented graphically and as numerical fits to a mathematical model of broad beam transmission to permit their use in the design of protective barriers for medical diagnostic x-ray facilities.

Calcium Sulfate↗

PubMedDate not supplied

Metareasoning and meta-level learning in a hybrid knowledge-based architecture.

Ahybrid knowledge-based architecture integrates different problem solvers for the same (sub)task through a control unit operating at a meta-level, the metareasoner, which coordinates the use of, and the communication between, the different problem solvers. A problem solver is defined to be an association between a knowledge intensive (sub)task, an inference mechanism and a knowledge domain view operated by the inference mechanism in order to perform the (sub)task. Important issues in a hybrid system are the metareasoning and learning aspects. Metareasoning encompasses the functions performed by the metareasoner, while learning reflects the ability of the system to evolve on the basis of its experiences in problem solving. Learning occurs at different levels, learning at the meta-level and learning at the level of the specific problem solvers. Meta-level learning reflects the ability of the metareasoner to improve the overall performance of the hybrid system by improving the efficiency of meta-level tasks. Meta-level tasks include the initial planning of problem solving strategies and the dynamic adaptation of chosen strategies depending on new events occurring dynamically during problem solving. In this paper we concentrate on metareasoning and meta-level learning in the context of a hybrid architecture. The theoretical arguments presented in the paper are demonstrated in practice through a hybrid knowledge-based prototype system for the domain of breast cancer histopathology.

Algorithms↗