Single-step affinity purification of recombinant proteins using a self-excising module from Neisseria meningitidis FrpC

Purification of recombinant proteins is often a challenging process involving several chromatographic steps that must be optimized for each target protein. Here, we developed a self-excising module allowing single-step affinity chromatography purification of untagged recombinant proteins. It consists of a 250-residue-long self-processing module of the Neisseria meningitidis FrpC protein with a C-terminal affinity tag. The N terminus of the module is fused to the C terminus of a target protein of interest. Upon binding of the fusion protein to an affinity matrix from cell lysate and washing out contaminating proteins, site-specific cleavage of the Asp-Pro bond linking the target protein to the self-excising module is induced by calcium ions. This results in the release of the target protein with only a single aspartic acid residue added at the C terminus, while the self-excising affinity module remains trapped on the affinity matrix. The system was successfully tested with several target proteins, including glutathione-S-transferase, maltose-binding protein, beta-galactosidase, chloramphenicol acetyltransferase, and adenylate cyclase, and two different affinity tags, chitin-binding domain or poly-His. Moreover, it was demonstrated that it can be applied as an alternative to two currently existing systems, based on the self-splicing intein of Saccharomyces cerevisiae and sortase A of Staphylococcus aureus.

Proteomic analysis uncovers a metabolic phenotype in C. elegans after nhr-40 reduction of function

Caenorhabditis elegans has an unexpectedly large number (284) of genes encoding nuclear hormone receptors, most of which are nematode-specific and are of unknown function. We have exploited comparative two-dimensional chromatography of synchronized cultures of wild type C. elegans larvae and a mutant in nhr-40 to determine if proteomic approaches will provide additional insight into gene function. Chromatofocusing, followed by reversed-phase chromatography and mass spectrometry, identified altered chromatographic patterns for a set of proteins, many of which function in muscle and metabolism. Prompted by the proteomic analysis, we find that the penetrance of the developmental phenotypes in the mutant is enhanced at low temperatures and by food restriction. The combination of our phenotypic and proteomic analysis strongly suggests that NHR-40 provides a link between metabolism and muscle development. Our results highlight the utility of comparative two-dimensional chromatography to provide a relatively rapid method to gain insight into gene function.

Epigenetic remodeling during arsenical-induced malignant transformation

Humans are exposed to arsenicals through many routes with the most common being in drinking water. Exposure to arsenic has been associated with an increase in the incidence of cancer of the skin, lung and bladder. Although the relationship between exposure and carcinogenesis is well documented, the mechanisms by which arsenic participates in tumorigenesis are not fully elucidated. We evaluated the potential epigenetic component of arsenical action by assessing the histone acetylation state of 13 000 human gene promoters in a cell line model of arsenical-mediated malignant transformation. We show changes in histone H3 acetylation occur during arsenical-induced malignant transformation that are linked to the expression state of the associated gene. DNA hypermethylation was detected in hypoacetylated promoters in the select cases analyzed. These epigenetic changes occurred frequently in the same promoters whether the selection was performed with arsenite [As(III)] or with monomethylarsonous acid, suggesting that these promoters were targeted in a non-random fashion, and probably occur in regions important in arsenical-induced malignant transformation. Taken together, these data suggest that arsenicals may participate in tumorigenesis by altering the epigenetic terrain of select genes.

Characterization of DESI-FTICR mass spectrometry - from ECD to accurate mass tissue analysis

Implementation of desorption electrospray ionization (DESI) technique on a 9.4 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer is described. Desorption electrospray technique is capable of the direct investigation of natural samples without any need for sample preparation or chromatographic separation. Since the DESI mass spectra of natural samples are very complex owing to the lack of preseparation or cleanup, the ideal mass spectrometric analyzer for these applications is a high-resolution instrument such as FTICR mass spectrometer. DESI was implemented by constructing an electronically controlled source framework comprising six linear moving stages and one rotating stage. A three-dimensional linear stage was used to accommodate samples, while another 3D linear stage equipped with rotating stage was used as a spray mount. A modified electrosonic sprayer was used as a primary electrospray device. DESI-FTICR setup was characterized with regard to geometrical, electrical and flow conditions using deposited peptide samples in range of 1-100 pmol gross deposited amount on glass and polymer surfaces. Optimized conditions enabled the routine acquisition of DESI-MS spectra on the instrument at 130 000 resolution in the broadband mode and with comparable sensitivity to data reported in the literature. Since the main significance of DESI-FTICR MS is the combination of intact tissue analysis, the capabilities of the technique were demonstrated by analyzing murine liver samples. Presence of lysophospholipids in the liver tissue was tentatively associated with the lipid metabolism taking place in liver. DESI-FTICR is also a promising technique in the field of peptide analysis due to capability of top-down sequencing using electron capture dissociation. As a proof-of-principle experiment, a small synthetic polypeptide containing 36 amino acids was ionized using DESI and was sequenced in the FTICR by means of ECD (electron capture dissociation) fragmentation. Spectra gave almost full sequence information in agreement with the known amino acid sequence of the species.

Intra-molecular cross-linking of acidic residues for protein structure studies

Intra-molecular cross-linking has been suggested as a method of obtaining distance constraints that would help to develop structural models of proteins. Recent work published on intra-molecular cross-linking for protein structural studies has employed commercially available primary amine (lysine, the amino terminus) selective reagents. Previous work using these cross-linkers has shown that for several proteins of known structure, the number of cross-links that can be obtained experimentally may be small compared to what would be expected from the known structure, due to the relative reactivity, distribution and solvent accessibility of the lysines in the protein sequence. To overcome these limitations, we have investigated the use of cross-linking reagents that can react with other reactive side chains in proteins. We used 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) to activate the carboxylic acid containing residues, aspartic acid (D), glutamic acid (E) and the carboxy terminus (O), for cross-linking reactions. Once activated, the DEO side chains can react to form "zero-length" cross-links with nearby primary amine containing residues, lysines (K) and the amino terminus (X), via the formation of a new amide bond. We also show that the EDC-activated DEO side chains can be cross-linked to each other using dihydrazides, two hydrazide moieties connected by an alkyl cross-linker arm of variable length. Using these reagents, we have found three new "zero-length" cross-links in ubiquitin consistent with its known structure (M1-E16, M1-E18 and K63-E64). Using the dihydrazide cross-linkers, we have identified two new cross-links (D21-D32 and E24-D32) unambiguously. Using a library of dihydrazide cross-linkers with varying arm length, we have shown that there is a minimum arm length required for the DEO-DEO cross-links of 5.8 A. These results show that additional structural information can be obtained by exploiting new cross-linker chemistry, increasing the probability that the protein target will yield sufficient distance constraints to develop a structural model.

Magnetic circular dichroism in electron energy loss spectrometry

The measurement of circular dichroism in the electron microscope is a new, emerging method and, as such, it is subject to constant refinement and improvement. Different ways can be envisaged to record the signal. We present an overview of the key steps in the energy-loss magnetic chiral dichroism (EMCD) experiment as well as a detailed review of the methods used in the intrinsic way where the specimen is used as a beam splitter. Lateral resolution up to 20-30 nm can be achieved, and the use of convergent beam techniques leads to an improved S/N ratio. Dichroic effects are shown for Ni and Co single crystal; as a counterexample, measurements were carried also for a non-magnetic (Ti) sample, where no dichroic effect was found.

Conductive interstitial thermal therapy (CITT) device evaluation in VX2 rabbit model

We have developed a conductive interstitial thermal therapy (CITT) device to precisely and reliably deliver controlled thermal doses to the surgical margins at the cavity site following tumor resection, intraoperatively. The temperature field created by CITT ablation of a perfused tissue was modeled with a finite element package Femlab. The modeling suggested that a maximum probe temperature of 120 degrees C and an ablation time of 20 minutes were required to ablate highly perfused tissue such as the VX2 carcinoma. Deployable pins enable faster and more reliable thermal ablation. The model predictions were tested by thermal ablation of VX2 carcinoma tumors implanted in adult New Zealand rabbits. The size of the ablated region was confirmed with a viability stain, triphenyltetrazolium chloride (TTC). Histopathological examination revealed 3 regions in the ablated area: a carbonized region (1-3 mm); a region that contained thermally fixed cells; and an area of coagulated necrosis cells. Cells in the thermally fixed region stained for PCNA (proliferating cell nuclear antigen) and were bounded by the carbonized layer at the cavity wall, and by necrotic cells that exhibit nuclear fragmentation and cell dissociation, 5 to 10 mm away from the CITT probe. Adjacent tissue outside the target region was spared with a clear demarcation between ablated and normal viable tissue. It is suggested that the CITT device can be used, clinically, to inhibit local recurrence by creating negative surgical margins following the resection of a primary tumor in non-metastatic early staged tumors.

Backbone Motions of Free and Pheromone-Bound Major Urinary Protein I Studied by Molecular Dynamics Simulation

Molecular motions of free and pheromone-bound mouse major urinary protein I, previously investigated by NMR relaxation, were simulated in 30 ns molecular dynamics (MD) runs. The backbone flexibility was described in terms of order parameters and correlation times, commonly used in the NMR relaxation analysis. Special attention was paid to the effect of conformational changes on the nanosecond time scale. Time-dependent order parameters were determined in order to separate motions occurring on different time scales. As an alternative approach, slow conformational changes were identified from the backbone torsion angle variances, and "conformationally filtered" order parameters were calculated for well-defined conformation states. A comparison of the data obtained for the free and pheromone-bound protein showed that some residues are more rigid in the bound form, but a larger portion of the protein becomes more flexible upon the pheromone binding. This finding is in general agreement with the NMR results. The higher flexibility observed on the fast (fs-ps) time scale was typically observed for the residues exhibiting higher conformational freedom on the ns time scale. An inspection of the hydrogen bond network provided a structural explanation for the flexibility differences between the free and pheromone-bound proteins in the simulations.

Unambiguous assignment of intramolecular chemical cross-links in modified mammalian membrane proteins by Fourier transform-tandem mass spectrometry

Fourier transform tandem mass spectrometry (FT-MS/MS) can be used to unambiguously assign intramolecular chemical cross-links to specific amino acid residues even when two or more possible cross-linking sites are adjacent in the cross-linked protein. Bovine rhodopsin (Rho) in its dark-adapted state was intramolecularly cross-linked with lysine-cysteine (K-C) or lysine-lysine (K-K) cross-linkers to obtain interatomic distance information. Large, multiply charged, cross-linked peptide ions containing adjacent lysines, corresponding to Rho(50-86) (K(66) or K(67)) cross-linked to Rho(310-317) (C(316)) or Rho(318-348) (K(325) or K(339)), were fragmented by collision-induced dissociation (CID), infrared multiphoton dissociation (IRMPD), and electron capture dissociation (ECD). Complementary sequence-specific information was obtained by combining cross-link assignments; however, only ECD revealed full palmitoylation of adjacent cysteines (C(322) and C(323)) and cross-linking of K(67) (and not K(66)) to C(316), K(325), and K(339). ECD spectra contained crucial c- and z-ions resulting from cleavage of the bond between K(66) and K(67). To our knowledge, this work also presents the first demonstration that ECD can be used to characterize S-linked fatty acid acylation on cysteines. The comprehensive fragmentation of large peptides by CID, IRMPD, and particularly ECD, in conjunction with the high resolution and mass accuracy of FT-MS/MS, is shown to be a valuable means of characterizing mammalian membrane proteins with both chemical and posttranslational modifications.

Chemical cross-linking and mass spectrometry as structure determination tools

Chemical cross-linking is becoming a valuable tool for the high-order structure determination of proteins and protein complexes. Cross-linking methodology is able to provide low-resolution structures when at least something is known already about the proteins under investigation. The suitability of top-down and bottom-up methodologies is discussed and further potential applications of chemical cross-linking of proteins, as well as combinations with other techniques such as hydrogen/deuterium exchange and molecular modeling, are suggested.

Monitoring conformational changes in protein complexes using chemical cross-linking and Fourier transform ion cyclotron resonance mass spectrometry: the effect of calcium binding on the calmodulin-melittin complex

Calmodulin is an EF hand calcium binding protein. Its binding affinities to various protein/peptide targets often depend on the conformational changes induced by the binding of calcium. One such target is melittin, which binds tightly to calmodulin in the presence of calcium, and inhibits its function. Chemical cross-linking combined with Fourier transform ion cyclotron resonance mass spectrometry has been employed to investigate the coordination of calmodulin and melittin in the complex at different concentrations of calcium. This methodology can be used to monitor structural changes of proteins induced by ligand binding, and study the effects these changes have on non- covalent interactions between proteins. Cross-linking results indicate that the binding place of the first melittin in the calcium free calmodulin form is the same as in the calcium loaded calmodulin/melittin complex.

Epigenetic inactivation of the HOXA gene cluster in breast cancer

Using an integrated approach of epigenomic scanning and gene expression profiling, we found aberrant methylation and epigenetic silencing of a small neighborhood of contiguous genes-the HOXA gene cluster in human breast cancer. The observed transcriptional repression was localized to approximately 100 kb of the HOXA gene cluster and did not extend to genes located upstream or downstream of the cluster. Bisulfite sequencing, chromatin immunoprecipitation, and quantitative reverse transcription-PCR analysis confirmed that the loss of expression of the HOXA gene cluster in human breast cancer is closely linked to aberrant DNA methylation and loss of permissive histone modifications in the region. Pharmacologic manipulations showed the importance of these aberrant epigenetic changes in gene silencing and support the hypothesis that aberrant DNA methylation is dominant to histone hypoacetylation. Overall, these data suggest that inactivation of the HOXA gene cluster in breast cancer may represent a new type of genomic lesion-epigenetic microdeletion. We predict that epigenetic microdeletions are common in human cancer and that they functionally resemble genetic microdeletions but are defined by epigenetic inactivation and transcriptional silencing of a relatively small set of contiguous genes along a chromosome, and that this type of genomic lesion is metastable and reversible in a classic epigenetic fashion.

Structure and dynamics of dark-state bovine rhodopsin revealed by chemical cross-linking and high-resolution mass spectrometry

Recent work using chemical cross-linking to define interresidue distance constraints in proteins has shown that these constraints are useful for testing tertiary structural models. We applied this approach to the G-protein-coupled receptor bovine rhodopsin in its native membrane using lysine- and cysteine-targeted bifunctional cross-linking reagents. Cross-linked proteolytic peptides of rhodopsin were identified by combined liquid chromatography and FT-ICR mass spectrometry with automated data-reduction and assignment software. Tandem mass spectrometry was used to verify cross-link assignments and locate the exact sites of cross-link attachment. Cross-links were observed to form between 10 pairs of residues in dark-state rhodopsin. For each pair, cross-linkers with a range of linker lengths were tested to determine an experimental distance-of-closest-approach (DCA) between reactive side-chain atoms. In all, 28 cross-links were identified using seven different cross-linking reagents. Molecular mechanics procedures were applied to published crystal structure data to calculate energetically achievable theoretical DCAs between reactive atoms without altering the position of the protein backbone. Experimentally measured DCAs are generally in good agreement with the theoretical DCAs. However, a cross-link between C316 and K325 in the C-terminal region cannot be rationalized by DCA simulations and suggests that backbone reorientation relative to the crystal coordinates occurs on the timescale of cross-linking reactions. Biochemical and spectroscopic data from other studies have found that the C-terminal region is highly mobile in solution and not fully represented by X-ray crystallography data. Our results show that chemical cross-linking can provide reliable three-dimensional structural information and insight into local conformational dynamics in a membrane protein.

Monitoring the effect of mild hyperthermia on tumour hypoxia by Cu-ATSM PET scanning

PURPOSE

Mild hyperthermia can improve tumour oxygenation and enhance radiosensitivity. Imaging the hypoxic fraction of a tumour can guide hyperthermia treatment planning and facilitate treatment optimization. 64Cu-ATSM (Copper-diacetyl-bis(N4-methylthiosemicarbazone)) is a positron emitting compound that has been demonstrated to have rapid uptake and selective retention in hypoxic cells and has been used for imaging human and animal tumours. The purpose of the present report is to establish methodology that will allow one to use Cu-ATSM PET scanning to detect the impact of hyperthermia on tumour physiology in as little time as possible.

MATERIALS AND METHODS

EMT6 tumours (mouse mammary carcinoma) were implanted into the subcutaneous tissue of both thighs of 10 BALB/c mice (one heated, one control tumour per animal). The target thermal dose was 41.5 degrees C x 45 min. Without interrupting heating, 64Cu-ATSM (mean activity 1.8 mCi) was then injected and serial PET scans were obtained. In a sub-group of four animals, a low administered activity (approximately 0.3 mCi) 64Cu-ATSM scan was also conducted before heating to permit a direct comparison of the effects of hyperthermia on the same tumours. In another sub-group of five animals, a low activity (approximately 0.3 mCi) 64Cu-PTSM (pyruvaldehyde-bis(N*-methylthiosemicarbazone)) scan was conducted before heating, to confirm a posited correlation between perfusion and early 64Cu-ATSM uptake.

RESULTS

This study corrected for perfusion differences by dividing tumour uptake by the average early (first minute) uptake ('self-normalized uptake'). The 10 heated tumours showed a significantly (p = 0.007) lower self-normalized uptake than control tumours by 2 min. For the four mice with low activity Cu-ATSM scans performed before hyperthermia, the tumours to be heated demonstrated self-normalized uptake consistent with the unheated control tumours and which departed significantly (p < or = 0.02) from their post-hyperthermia scans by 5 min. Comparisons between scans and needle electrode surveys were performed in an additional four animals with eight tumours. For technical reasons electrode surveys were done after the end of hyperthermia-and, therefore, these animals also had comparison scans taken after hyperthermia. Reduced self-normalized uptake on scans was associated with increased pO2 on electrode surveys. These data also suggested a substantial degradation of the effect on tumour hypoxia by approximately 15-45 min after the end of mild hyperthermia.

CONCLUSION

Short imaging times of approximately 5 min with modest (approximately 4-10) numbers of mice can discriminate the effects of mild hyperthermia on tumour physiology. The long-term objective is to use this tool to identify as short and mild a hyperthermia session as possible.

Electromagnetic and thermal characterization of an UHF-applicator for concurrent irradiation and high resolution non-perturbing optical microscopy of cells

To permit trans-illuminated, high-resolution optical microscopy during unperturbed ultrahigh frequency (UHF) irradiation, a novel new class of applicator has been designed based upon a shielded-pair transmission line. As constructed and tested with water-immersion optics and air cooling, the applicator works most robustly over 700-1100 MHz and permits SARs at the cell layer as high as 50 W/kg before the steady state temperature rise at the cell-layer exceeds 0.5 K.

Synthesis of C-Aryldeoxyribosides by [2 + 2 + 2]-Cyclotrimerization Catalyzed by Rh, Ni, Co, and Ru Complexes

[reaction: see text] A novel approach to the synthesis of functionalized C-nucleosides was developed. Cyclotrimerization of C-alkynyldeoxyriboside with a variety of substituted 1,6-heptadiynes to the corresponding C-aryldeoxyribosides was catalyzed by various transition metal complexes (Rh, Ir, Co, Ru, and Ni). The most general catalyst proved to be RhCl(PPh(3))(3), which could catalyze most of the cyclotrimerizations in high yields (52-95%).

High-resolution ultrahigh-field MRI of stroke

BACKGROUND

Ultrahigh-field MRI at 8 T offers unprecedented resolution for imaging brain structures and microvasculature.

OBJECTIVE

The aim of this study is to apply high-resolution MRI for stroke imaging and to characterize findings at 1.5 and 8 T.

METHODS

Seventeen subjects with minor ischemic infarcts were studied using T2-weighted gradient echo (GE) and rapid acquisition with relaxation enhancement (RARE) images at 8 T with resolution up to 200 microm. In 10 subjects, T1- and T2-weighted fast spin echo (FSE) and fluid-attenuated inversion recovery (FLAIR) images were also acquired at 1.5-T MRI.

RESULTS

The 8-T images showed infarcts as sharply demarcated areas of high-signal intensity (n=21) and revealed more infarctions than 1.5-T images (n=14) (P<.003). The low-signal intensity areas that surrounded infarctions were suggestive of hemosiderin deposits. The 8-T characteristics of microvessels terminating within the infractions were distinct from normal vasculature. The 8-T images revealed an angioma at the site of a second stroke, not apparent on 1.5-T images.

CONCLUSIONS

Ultrahigh-field MRI at 8 T is feasible for stroke imaging. The 8-T MRI visualized infarcts and microvasculature with high resolution, revealing infarcts and vascular pathologies that were not apparent at 1.5 T.

Localized versus regional hyperthermia: comparison of xenotransplants treated with a small animal ultrasound system and waterbath limb immersion

The response of xenotransplants were compared with waterbath immersion vs focal ultrasound (US) hyperthermia using tumour growth delay, immunhistochemistry and histopathology assays. Waterbath hyperthermia was performed by limb immersion. Precautions were taken to minimize total body heating by surrounding the mouse with plastic insulators. Thermometry was performed with clinical-grade, 20-gauge needle thermocouples and monitored with a Labthermics unit. Significant differences in cytotoxicity between ultrasound and waterbath treatment of tumors at 43 degrees C were observed as determined by TUNNEL assay. Conversely, contralateral (non-treated) tumours in animals treated with similar temperature demonstrated no significant differences between modalities. Western blot analysis revealed increased hsp70 induction at 43 degrees C in waterbath vs focal ultrasound hyperthermia. Comparison of tumour growth delay between tumours heated with waterbath vs ultrasound at 43 degrees C but not at 41 degrees C revealed significant differences. This is the first study comparing localized vs regional hyperthermia using the small animal ultrasound system (SAHUS) delivery system. Consistent ultrasound hyperthermia can be achieved throughout a xenotransplant. At equivalent temperature of 43 degrees C for 60?min, waterbath hyperthermia demonstrated greater local response vs ultrasound hyperthermia.

Macromolecular prodrugs XI. Synthesis and characterization of polymer-estradiol conjugate

Estradiol-3-benzoate (EB), an ester derivative of the main oestrogen hormone estradiol, was chemically modified and bound to poly(alpha,beta-(N-2-hydroxyethyl-DL-aspartamide))-poly(alpha,beta-(N-2-aminoethyl-DL-aspartamide)) copolymer (PAHA). EB was first converted to estradiol-3-benzoate-17-(benzotriazole-1-carboxylate), which readily reacted with amino groups in PAHA affording the polymer-drug conjugate PAHA-EB. In PAHA-EB estradiol moiety was covalently bound to the polymeric carrier by carbamate linkage, through non-toxic ethylenediamine spacer. The synthesized compound is a potential hydrosoluble estradiol prodrug.

Disproportionation, metal-insulator transition, and critical interaction strength in Na(1/2)CoO2

Charge disproportionation (CD) and spin differentiation in Na(1/2)CoO2 are studied using the correlated band local-density approximation + Hubbard U (LDA+U) approach. The simultaneous CD and gap opening seen previously is followed in detail through a first-order charge disproportionation transition 2Co(3.5+)-->Co3++Co4+. Disproportionation in the Co a(g) orbital results in half of the ions (Co3+) becoming electronically and magnetically dead, transforming the quarter-filled a(g) system into a half-filled subsystem that subsequently undergoes the observed charge ordering or metal-insulator transition. Comparing with data in the x approximately 0.3 regime suggests the system has moved into the multiband regime where the effective Coulomb repulsion U-->U(eff)=U/sqrt[3] strongly lessens correlation effects.

Strategy for selective chemical cross-linking of tyrosine and lysine residues

Chemical cross-linking of proteins combined with mass spectral analysis is a powerful technique that can be utilized to yield protein structural information, such as the spatial arrangement of multi-protein complexes or the folding of monomeric proteins. The succinimidyl ester cross-linking reagents are commonly used to cross-link primary amine-containing amino acids (N-terminus and lysine). However, in this study they were used to react with tyrosines as well, which allowed for the formation of cross-links between two primary amines, one primary amine and one tyrosine, or two tyrosines. This result is extremely important to the chemical cross-linking community for two reasons: (1) all possible cross-linked residues must be considered when analyzing data from these experiments to generate correct distance constraints and structural information, and (2) utilizing the versatility of these cross-linking reagents allows more information content to be generated from a single cross-linking reagent, which may increase the number of cross-links obtained in the experiment. Herein, we study the reactivity of the succinimidyl ester labeling and cross-linking reagents with angiotensin I and oxidized insulin beta-chain. Using the succinimidyl acetate labeling reagent, the reactivity of the N-terminus was found to be greater than either lysine or tyrosine. However, a selectivity of the cross-linking reagent was observed for either tyrosine or lysine depending on the pH of the reaction solution. In acidic pH, it was observed that tyrosine was more reactive, while in alkaline pH lysine was more reactive. Exploiting this selectivity predominantly N-terminus-tyrosine or tyrosine-tyrosine cross-links were favored at acidic pH, while N-terminus-tyrosine or tyrosine-lysine cross-links were favored at alkaline pH.

A top-down method for the determination of residue-specific solvent accessibility in proteins

We present a method employing top-down Fourier transform mass spectrometry (FTMS) for the rapid profiling of amino acid side-chain reactivity. The reactivity of side-chain groups can be used to infer residue-specific solvent accessibility and can also be used in the same way as H/D exchange reactions to probe protein structure and interactions. We probed the reactivity of the N-terminal and epsilon-lysine amino groups of ubiquitin by reaction with N-hydroxysuccinimidyl acetate (NHSAc), which specifically acetylates primary amines. Using a hybrid Q-FTMS instrument, we observed several series of multiply acetylated ubiquitin ions that varied with the NHSAc:protein stoichiometry. We isolated and fragmented each member of the series of acetylated ubiquitin ions in the front end of the instrument and measured the fragment ion masses in the FTMS analyzer cell to determine which residue positions were modified. As we increased the NHSAc:protein stoichiometric ratio, identification of the fragments from native protein and protein with successively increasing modification allowed the assignment of the complete order of reactivity of the primary amino groups in ubiquitin (Met 1 approximately Lys 6 approximately Lys 48 approximately Lys 63>Lys 33>Lys 11>Lys 27, Lys 29). These results are in excellent agreement with the reactivity expected from other studies and predicted from the known crystal structure of ubiquitin. The top-down approach eliminates the need for proteolytic digestion, high-performance liquid chromatographic separations and all other chemical steps except the labeling reaction, making it rapid and amenable to automation using small quantities of protein.

Thermal contribution of compact bone to intervening tissue-like media exposed to planar ultrasound

The presence of bone in the ultrasound beam path raises concerns, both in diagnostic and therapeutic applications, because significant temperature elevations may be induced at nearby soft tissue-bone interfaces due the facts that ultrasound is (i) highly absorbed in bone and (ii) reflected at soft tissue-bone interfaces in various degrees depending on angle of incidence. Consequently, in ultrasonic thermal therapy, the presence of bone in the ultrasound beam path is considered a major disadvantage and it is usually avoided. However, based on clinical experience and previous theoretical studies, we hypothesized that the presence of bone in superficial unfocused ultrasound hyperthermia can actually be exploited to induce more uniform and enhanced (with respect to the no-bone situation) temperature distributions in superficial target volumes. In particular, we hypothesize that the presence of underlying bone in superficial target volume enhances temperature elevation not only by additional direct power deposition from acoustic reflection, but also from thermal diffusion from the underlying bone. Here we report laboratory results that corroborate previous computational studies and strengthen the above-stated hypothesis. Three different temperature measurement techniques, namely, thermometric (using fibre-optic temperature probes), thermographic (using an infrared camera) and magnetic resonance imaging (using proton resonance frequency shifts), were used in high-power short-exposure, and in low-power extended-exposure, experiments using a 19 mm diameter planar transducer operating at 1.0 and 3.3 MHz (frequencies of clinical relevance). The measurements were performed on three technique-specific phantoms (with and without bone inclusions) and experimental set-ups that resembled possible superficial ultrasound hyperthermia clinical situations. Results from all three techniques were in general agreement and clearly showed that significantly higher heating rates (greater than fourfold) were induced in soft tissue-like phantom materials adjacent (within approximately 5 mm) to a bovine bone as compared to similar experiments without bone inclusions. For low-power long-exposure experiments, where thermal conduction effects are significant, the thermal impact of bone reached at distances > 10 mm from the bone surface (upstream of the bone). Therefore, we hypothesize that underlying bone exposed to planar ultrasound hyperthermia creates a high-temperature thermal boundary at depth that compensates for beam attenuation, thus producing more uniform temperature distribution in the intervening tissue layers. With appropriate technology, this finding may lead to improved thermal doses in superficial treatment sites such as the chest wall and the head/neck.

Altered cerebral vasoregulation in hypertension and stroke

BACKGROUND

Autoregulation of blood flow that maintains steady perfusion over the range of systemic blood pressure is compromised by stroke.

OBJECTIVES

To determine whether cerebral vasoregulation is impaired in stroke during orthostatic stress.

METHODS

Subjects included 30 control subjects, 30 with hypertension, and 20 with minor stroke and were studied using transcranial Doppler. Bilateral blood flow velocities (BFVs) from middle cerebral arteries, heart rate, blood pressure (BP), and CO2 were obtained during hyperventilation and CO2 rebreathing during supine rest and tilt at 80 degrees. Side-to-side BFV difference, vasomotor range (VMR), and cerebrovascular resistance (CVR) were calculated during normo-, hypo-, and hypercapnia.

RESULTS

Mean BFVs were similar between groups in supine position but differed during tilt. BFV diminished on the stroke side during tilt with hyperventilation and CO2 rebreathing (p < 0.0001). CVR increased (p < 0.0001) and VMR decreased (p < 0.01) on the stroke side. Vasoregulation was preserved on the normal side. BFV asymmetry differentiated patients with stroke from the other groups (p < 0.0001). BFV difference between the normal vs stroke side was the largest in stroke-normotensive (n = 7) compared with stroke-hypertensive (n = 13) patients and the two other groups (p < 0.0001). BFV asymmetry in stroke was associated with lower orthostatic BP (p < 0.0001).

CONCLUSIONS

Cerebral vasoregulation is impaired with minor stroke, and cerebral blood flow depends on blood pressure. Decline of blood flow velocities during orthostatic stress may pose a risk of silent hypoperfusion.

A top-down approach to protein structure studies using chemical cross-linking and Fourier transform mass spectrometry

In a preliminary communication we described a top-down approach to the determination of chemical cross-link location in proteins using Fourier transform mass spectrometry (FT-MS). We have since extended the approach to use a series of homobifunctional cross-linkers with the same reactive functional groups, but different cross-linker arm lengths. Correlating cross-linking data across a series of related linkers allows the distance constraint derived from a cross-link between two reactive side chains to be determined more accurately and increases the confidence in the assignment of the cross-links. In ubiquitin, there are seven lysines with primary amino groups and the amino terminus. Disuccinimidyl suberate (DSS, cross-linker arm length = 11.4 A), disuccinimidyl glutarate (DSG, cross-linker arm length = 7.5 A) and disuccinimidyl tartrate (DST, cross- linker arm length = 5.8 A) are homobifunctional cross-linking reagents that react specifically with primary amines. Using tandem mass spectrometry (MS/MS) on the singly, internally cross-linked precursor ion of ubiquitin, we found cross-links with DSS and DSG between the amino terminus and Lys 6, between Lys 6 and Lys 11, and between Lys 63 and Lys 48. Using disuccinimidyl tartrate (DST), the shortest cross-linker in the series, only the cross-links between the amino terminus and Lys 6, and between Lys 6 and Lys 11 were observed. The observed cross-links are consistent with the crystal structure of ubiquitin, if the lysine side chains and the amino terminus are assumed to have considerable flexibility. In a separate study, we probed the reactivity of the primary amino groups in ubiquitin using the amino acetylating reagent, N-hydroxy succinimidyl acetate (NHSAc), and a top-down approach to localize the acetylated lysine residues. The reactivity order obtained in that study (M1 approximate, equals K6 approximate, equals K48 approximate, equals K63) > K33 > K11 > (K27, K29), shows that the cross-link first formed in ubiquitin by reaction with DSS and DSG occurs between the most reactive residues.

New derivatives of tylosin: chemical and electrochemical oxidation products of desmycosin

Chemical and electrochemical oxidation of dienonic moiety of desmycosin were carried out. Successive chemical oxidation of desmycosin with m-chloroperbenzoic acid afforded a family of 12,13-dihydro-12,13-dihydroxy derivatives. Indirect electrochemical oxidation via hypobromite as an intermediate gave rise to the new bicyclo derivative of desmycosin, 13-hydroxy-3-dehydroxy-3,12-oxa-desmycosin.

Intracranial ossifications and microangiopathy at 8 Tesla MRI

Clinical evaluation and MR imaging of microangiopathy associated with hypertension is limited. We describe a case that illustrates sensitivity of MRI at 8 Tesla for imaging of microvasculature, iron, calcium deposits and silent white matter lesions (WML). A 60-year-old black hypertensive woman was evaluated for numbness in the face and extremities. MRI at 1.5 Tesla was unrevealing.MRI at 8 Tesla: Axial and sagittal Gradient Echo images were obtained with an 8T/80 cm human scanner and showed: 1) Large areas of signal voids due to ossifications and fat deposits within the falx. 2) Obstructed small vessels in the periventricular regions and distended cortical veins. 3) Numerous small WML, suggestive of mini-infarcts (<1 cm) and microhemorrhages. 4) Intracranial calcifications in the falx, tentorium, basal ganglia and chorioid plexus that were confirmed by CT scan. Atherosclerotic plaque in right carotid artery and reduced vasomotor reserve in middle cerebral arteries, documented by ultrasound, indicated large and small vessel disease.

CONCLUSIONS

MRI at 8 Tesla improves visualization of microangiopathy, ossifications and iron deposits due to enhanced magnetic susceptibility at ultra high magnetic field.

Peritoneal mesothelial hypoxia during pneumoperitoneum is a cofactor in adhesion formation in a laparoscopic mouse model

OBJECTIVE

To develop a laparoscopic mouse model to evaluate the hypothesis that mesothelial hypoxia during pneumoperitoneum is a cofactor in adhesion formation.

DESIGN

Prospective randomized trials.

SETTING

Academic research center.

ANIMAL(S)

One hundred thirty female Naval Medical Research Institute (NMRI) mice.

INTERVENTION(S)

Adhesions were induced by opposing monopolar lesions in uterine horns and pelvic side walls during laparoscopy and evaluated after 7 or 28 days under microscopic vision during laparotomy. The following pneumoperitoneum variables were assessed: duration (10 or 60 minutes), insufflation pressure (5 or 15 cm of water), insufflation gas (CO(2) or helium), and addition of oxygen (0-12%).

MAIN OUTCOME MEASURE(S)

Adhesions were scored quantitatively and qualitatively for extent, type, and tenacity.

RESULT(S)

Scoring of adhesions 7 or 28 days after laparoscopic surgery was comparable. Adhesions increased with duration of pneumoperitoneum and with insufflation pressure and decreased with the addition of oxygen. Half-maximal reduction of adhesions was obtained at 1.5% oxygen, whereas a maximal reduction required only 2%-3%. The effect of CO(2) and helium was similar.

CONCLUSION(S)

These data demonstrate the feasibility of the intubated laparoscopic mouse model and confirm previous observations in rabbits, indicating that mesothelial hypoxia plays a key role in adhesion formation.

Ultra High Field MRI at 8 Tesla of Subacute Hemorrhagic Stroke

PURPOSE

Optimal treatment strategies and neurologic outcome after stroke depend on an accurate characterization of the lesion. There is a need for high resolution noninvasive imaging for assessment of the infarct size, perfusion, and vascular territory. MRI at the ultra high field (UHF) of 8 T offers unprecedented resolution, but its utility for stroke evaluation has not been determined yet.

METHOD

A 55-year-old man with hypertension experienced sudden onset of speech arrest and right-sided hemiparesis that resolved in < 24 h with minimal neurologic deficit. MRI at 1.5 T showed initially a left posterior frontal lesion with subacute infarct (hyperintense on T2-weighted spin echo images) and right-sided frontal and periventricular lesions consistent with chronic infarct. There were many smaller white matter lesions. Delayed studies showed high signal changes involving the gray matter only on T1-weighted images.

RESULTS

Gradient echo and rapid acquisition with relaxation enhancement (RARE) multislice images revealed a serpentine area of low signal in the left posterior frontal lobe gray matter suggestive of a hemorrhagic infarct, right-sided frontal lesion also showing iron deposits, multiple periventricular and cortical areas with abnormal high signal regions that were consistent with old infarcts, and numerous small vessels readily visible, more prominent on the right.

CONCLUSION

MRI at 8 T displays lesions with a high resolution and striking anatomic details. Susceptibility to iron and sensitivity to detect blood products are increased at 8 T. The imaging characteristics at high field are different from those at low field, but both represent findings of iron products.

High resolution MRI of the brainstem at 8 T

A recently developed ultra high field MRI system operating at 8 T (UHFMRI) was applied for brainstem imaging. UHFMRI was performed in five healthy volunteers (three men, two women; age range 34--46 years). Sagittal and axial slices were obtained with the following settings: GE, TR 750--1,000 ms, TE 7-9 ms, FOV 20 cm, matrix 1,024 x 1,024 or 512 x 512 points, slice thickness 2 mm, resolution 195 or 390 microm/pixel. The brainstem structures were assigned based on anatomy and course. Images with good signal strength and homogeneity were acquired from the midbrain and the pons. Main intraaxial structures could be directly visualized. The periaqueductal gray matter and nuclei had higher signal intensity than the predominantly white matter structures such as the corticobulbar/corticopontine/corticospinal tracts, the sensory lemnisci, and the medial longitudinal fasciculus. Structures with high iron content such as the substantia nigra and the red nucleus were seen as prominent signal hypointensities. Numerous vessels traversing the brainstem including small perforators were also distinguished. It is concluded that UHFMRI enables the acquisition of high quality images of the upper brainstem with details approaching that of histologic specimen.

[1998 social epidemiological analysis of caries incidence and degree of dental restoration in young men]

Basing on the hypothesis that adult dental health is co-determined by the conditions and influences prevailing in the family of origin during childhood and adolescence, we analysed the associations of socio-economic status of the family, personal dental care behaviour and other educational and structural factors, with caries prevalence (DMF-T) and the level of restoration in 642 young men between 18 and 24 years eligible for conscription. Additionally, we presented the changes in caries prevalence in conscripted persons during the 1990s comparing our results with those of a study conducted in 1989-90.

RESULTS

The average number of DMF-T teeth was 5.7. 15% of subjects were caries-free. The mean level of restoration in those with a history of caries was 79.2%. The prevalence of caries and the level of restoration were strongly associated with the level of education, and the socio-economic status of the family of origin. Parental working time, number of siblings, structural deficiencies in the family, parental preventive education and training with regard to dental care, frequency of brushing the teeth, belief in the success of preventive health measures and prevalence of fissure sealings were significantly associated with DMF-T. Frequency of dental visits showed an association with the level of restoration. From 1989/90 to 1998 prevalence of caries in conscripts decreased by 42% (after adjusting for the different levels of education of both studies the decrease was 36%). Whereas in 1989/90 the average number of DMF-T in the 9-year elementary school graduates exceeded those of the high school graduates ("seniors") by 22%, this difference increased to 88% by 1998. More than 40% of the differences in the prevalence of caries among subjects of different educational levels were due to risk factors of social origin, preventive dental behaviour and utilisation of dental services, all of these being less favourable in elementary school or secondary school graduates compared to high-school graduates.

Eating habits, health status, and concern about health: a study among 1641 employees in the German metal industry

BACKGROUND

Nutrition has been found to be associated with sociodemographic characteristics and concern about health. There is limited knowledge, however, of associations between blue-collar worker's diet, morbidity, and health care utilization.

METHODS

We conducted a survey on eating habits, physical symptoms, health care utilization, health status, and concern about health in two German metal companies. A self-administered questionnaire was mailed to employees of whom 1641 participated in the study (response rate 54. 7%).

RESULTS

Most employees were characterized by a combination of healthy and unhealthy eating elements. Using linear regression analyses adjusted for age, gender, and occupational status, healthy eating was negatively associated with stomach aches and headaches, but not with cardiovascular disease. Restricted activity days and days in hospital were associated with healthy eating, but self-assessed health status and physician consultations were not. Using stepwise multiple regression analysis, age, gender, and concern about health were strongly and morbidity was weakly related to diet. Occupational status, marital status, and number of children were not associated with nutrition.

CONCLUSIONS

Health promotion programs should motivate younger and male employees to participate in and aim toward increasing concern about health.