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C J Thomas

Publications and source records attributed to C J Thomas.

At least 37 records · Page 2Linked to original sources
PubMed2000

On the stringent requirement of mannosyl substitution in mannooligosaccharides for the recognition by garlic (Allium sativum) lectin. A Surface Plasmon Resonance Study.

The kinetics of the binding of mannooligosaccharides to the heterodimeric lectin from garlic bulbs was studied using surface plasmon resonance. The interaction of the bound lectin immobilized on the sensor chip with a selected group of high mannose oligosaccharides was monitored in real time with the change in response units. This investigation corroborates our earlier study about the special preference of garlic lectin for terminal alpha-1,2-linked mannose residues. An increase in binding propensity can be directly correlated to the addition of alpha-1,2-linked mannose to the mannooligosaccharide at its nonreducing end. Mannononase glycopeptide (Man9GlcNAc2Asn), the highest oligomer studied, exhibited the greatest binding affinity (Ka = 1.2 x 10(6) m(-1) at 25 degrees C). An analysis of these data reveals that the alpha-1,2-linked terminal mannose on the alpha-1,6 arm is the critical determinant in the recognition of mannooligosaccharides by the lectin. The association (k1) and dissociation rate constants (k(-1)) for the binding of Man9GlcNAc2Asn to Allium sativum agglutinin I are 6.1 x 10(4) m(-1) s(-1) and 4.9 x 10(-2) s(-1), respectively, at 25 degrees C. Whereas k1 increases progressively from Man3 to Man7 derivatives, and more dramatically so for Man8 and Man9 derivatives, k(-1) decreases relatively much less gradually from Man3 to Man9 structures. An unprecedented increase in the association rate constant for interaction with Allium sativum agglutinin I with the structure of the oligosaccharide ligand constitutes a significant finding in protein-sugar recognition.

Agglutinins↗
PubMed2000

Interaction of chloroquine and its analogues with heme: An isothermal titration calorimetric study.

Quinoline-containing drugs such as chloroquine and quinine have had a long and successful history in antimalarial chemotherapy. Identification of ferriprotoporphyrin IX ([Fe(III)PPIX], haematin) as the drug receptors for these antimalarials called for investigations of the binding affinity, mode of interaction, and the conditions affecting the interaction. The parameters obtained are significant in recent times with the emergence of chloroquine resistant strains of the malaria parasites. This has underlined the need to unravel the molecular mechanism of their action so as to meet the requirement of an alternative to the existing antimalarial drugs. The isothermal titration calorimetric studies on the interaction of chloroquine with haematin lead us to propose an altered mode of binding. The initial recognition is ionic in nature mediated by the propionyl group of haematin with the quaternary nitrogen on CQ. This ionic interaction induces a conformational change, such as to favour binding of subsequent CQ molecules. On the contrary, conditions emulating the cytosolic environment (pH 7.4 and 150 mM salt) reveal the hydrophobic force to be the sole contributor driving the interaction. Interaction of a carefully selected panel of quinoline antimalarial drugs with monomeric ferriprotoporphyrin IX has also been investigated at pH 5.6 mimicking the acidic environment prevalent in the food vacuoles of parasite, the center of drug activity, which are consistent with their antimalarial activity.

Amodiaquine↗
PubMed2000

Kinetics and the mechanism of interaction of the endoplasmic reticulum chaperone, calreticulin, with monoglucosylated (Glc1Man9GlcNAc2) substrate.

Calreticulin is a lectin-like molecular chaperone of the endoplasmic reticulum in eukaryotes. Its interaction with N-glycosylated polypeptides is mediated by the glycan, Glc(1)Man(9)GlcNAc(2), present on the target glycoproteins. In this work, binding of monoglucosyl IgG (chicken) substrate to calreticulin has been studied using real time association kinetics of the interaction with the biosensor based on surface plasmon resonance (SPR). By SPR, accurate association and dissociation rate constants were determined, and these yielded a micromolar association constant. The nature of reaction was unaffected by immobilization of either of the reactants. The Scatchard analysis values for K(a) agreed well with the one obtained by the ratio k(1)/k(-1). The interaction was completely inhibited by free oligosaccharide, Glc(1)Man(9)GlcNAc(2,) whereas Man(9)GlcNAc(2) did not bind to the calreticulin-substrate complex, attesting to the exquisite specificity of this interaction. The binding of calreticulin to IgG was used for the development of immunoassay and the relative affinity of the lectin-substrate association was indirectly measured. The values are in agreement with those obtained with SPR. Although the reactions are several orders of magnitude slower than the diffusion controlled processes, the data are qualitatively and quantitatively consistent with single-step bimolecular association and dissociation reaction. Analyses of the activation parameters indicate that reaction is enthalpically driven and does not involve a highly ordered transition state. Based on these data, the mechanism of its chaperone activity is briefly discussed.

Animals↗
PubMed2000

The spatial distribution and size of rook (Corvus frugilegus) breeding colonies is affected by both the distribution of foraging habitat and by intercolony competition.

Explanations for the variation in the number of nests at bird colonies have focused on competitive or habitat effects without considering potential interactions between the two. For the rook, a colonial corvid which breeds seasonally but forages around the colony throughout the year, both the amount of foraging habitat and its interaction with the number of competitors from surrounding colonies are important predictors of colony size. The distance over which these effects are strongest indicates that, for rooks, colony size may be limited outside of the breeding season when colony foraging ranges are larger and overlap to a greater extent.

Animals↗
PubMed2000

Mode of molecular recognition of L-fucose by fucose-binding legume lectins.

Recognition of cell surface carbohydrate moieties by lectins plays a vital role in many a biological process. Fucosyated residues are often implicated as key recognition markers in many cellular processes. In particular, the aspects of molecular recognition of fucose by fucose-bindinglectins UEA 1 and LTA pose a special case because no crystal structure of these lectins is available. The study was conducted to elucidate the process of recognition of l-fucose by UEA1 and LTA by correlating structure-based sequence alignment and other available biochemical/biophysical data. The study points out that the mode of recognition of l-fucose is coordinated by the invariant triad of residues the asparagine 137, glycine 105, and aspartate 87. The major hydrophobic stacking residue in this case is the tyrosine 220. The study also reiterates the key role of the conserved triad of residues in the combining site which is a common feature for all legume lectins whose crystal structures are known.

Amino Acid Sequence↗
PubMed2000

Kinetic analysis of the binding of Ulex europeas agglutinin 1 (UEA 1) to H-antigenic fucolipid.

The kinetics and thermodynamics of Ulex europeas agglutinin 1-H-antigenic determinant was studied by monitoring the binding of the lectin to H-antigenic fucolipid incorporated in liposomes tethered to the sensor surface by surface plasmon resonance. The second-order rate constants for the interactions are several order of magnitude slower than the diffusion controlled reactions. Analyses of activation parameters reveals that these slow second-order rate constants are a consequence of an unfavorable activation enthalpy term.

ABO Blood-Group System↗
PubMed2000

Titanium for removable partial dentures (III): 2-year clinical follow-up in an undergraduate programme.

This study examined the success of titanium (Ti) removable partial dentures (RPDs) compared with that of cobalt-chromium (Co-Cr) RPDs using a randomized controlled clinical trial. Thirty-eight RPD patients were provided with either Co-Cr (20 patients) or Ti (18 patients) RPDs. The total numbers of dentures was 31 (13 maxillary, 18 mandibular) for Co-Cr and 23 (11 maxillary, 12 mandibular) for Ti. Patients were reviewed for 24 months following denture issue. After the initial 12 months, 20 clinical problems were recorded and became the criteria for subsequent assessment. Incidence of failure was analysed using both Fisher's exact test and the chi square test at a significance level of P<0.05. Fracture of retainers in both metals occurred only in the first 12 months. Some failure types presented at significantly higher levels in the first 12 months but there were no significant differences between the two in all the criteria examined between the 12- and the 24-month reviews. Although differences existed in failure types between Co-Cr and Ti RPDs during the early review stages, the overall success rate of Ti RPDs was comparable with that of Co-Cr RPDs after 24 months. The higher incidence of failures in Ti RPDs prior to the 12-month review suggests the importance of taking its lower rigidity into account when designing RPDs.

Chi-Square Distribution↗
PubMed2000

Mutagenesis of the active site coding region of the Autographa californica nucleopolyhedrovirus chiA gene.

The chitinase of Autographa californica nucleopolyhedrovirus (AcMNPV) is required for the characteristic liquefaction of baculovirus-infected insect larvae. Alignments of the putative active sites of a range of chitinases revealed two highly conserved residues, glutamate and aspartate, which have been proposed to constitute the catalytic residues of the active site. These residues were mutated in the AcMNPV chitinase. Three recombinant viruses were generated, AcchiA(D311G), AcchiA(E315G) and AcchiA(D311G E315G), which contained mutations at either the glutamate, the aspartate or both. It was demonstrated that chitinase protein production was unaffected by the mutation of these residues. However, mutation of both residues resulted in the attenuation of chitinolytic activity and the cessation of liquefaction of Trichoplusia ni larvae infected with AcchiA(D311G E315G). Mutagenesis of the glutamate residue led to a reduction in exochitinase activity and a delay in the appearance of endochitinase activity. In addition, larvae infected with this virus, AcchiA(E315G), liquefied more slowly than those larvae infected with wild-type AcMNPV. Mutagenesis of the aspartate residue resulted in a reduction of exochitinase activity but an unexpected enhancement of endochitinolytic activity. Liquefaction of AcchiA(D311G)-infected larvae was observed at the same time as that of AcMNPV-infected larvae.

Animals↗
PubMed1999

Surface plasmon resonance studies resolve the enigmatic endotoxin neutralizing activity of polymyxin B.

Polymyxin B (PMB), a cyclic cationic peptide antibiotic, despite its severe side effects continues to occupy a premiere position for treating endotoxicosis. Its mode of neutralization of endotoxin has remained elusive for the last three decades. Several synthetic peptide mimics of PMB, capable of binding endotoxin, have been made. However, the binding ability alone appears to be a deceptive indicator of endotoxin neutralizing activity as molecules with similar binding propensities could either sequester or opsonize the toxin. Hence identification of additional physical parameters which describe adequately the outcome of PMB-endotoxin interaction become imperative. Surface plasmon resonance (SPR) studies reported here show that several mimics of PMB despite exhibiting lipopolysaccharide binding affinities comparable with it but, unlike it, do not sequester the endotoxin. These studies thus provide a striking illustration of the difference in the behavior of PMB, vis a vis its mimics toward the endotoxin lamellae, and define further, in chemical terms, mechanism of the action of PMB and allow us to posit that the design of molecules as effective antidotes for sepsis should incorporate the ability to sequester endotoxin specifically.

Amino Acid Sequence↗
PubMed1999

Thermodynamic and kinetic analysis of the Escherichia coli thioredoxin-C' fragment complementation system.

Escherichia coli thioredoxin was cleaved with CNBr at its single Met residue at position 37, which lies in the middle of a long alpha-helix. The two fragments, 1-37 and 38-108, were purified and characterized by using CD and fluorescence spectroscopy. Both fragments lack structure at neutral pH and room temperature. The secondary and tertiary structural contents of the non-covalent complex formed on the mixing of the two peptide fragments are 47% and 35% of the intact protein respectively. The thermodynamics and kinetics of fragment association were characterized by titration calorimetry and stopped-flow fluorescence spectroscopy. Single phases were observed for both association and dissociation, with rate constants at 298 K of kon=4971+/-160 M-1.s -1 and koff=0. 063+/-0.009 s-1 respectively. The ratio kon/koff was very similar to the binding constant determined by titration calorimetry, suggesting that binding is a two-state process. The values for DeltaCp, DeltaH0 and DeltaG0 at 298 K for dissociation of the complex were 5.7 kJ. mol-1.K-1, 45.3 kJ.mol-1 and 29.8 kJ.mol-1 respectively. The value for DeltaH0 was linearly dependent on temperature from 8-40 degrees C, suggesting that DeltaCp is independent of temperature. The values for DeltaCp and DeltaG0 are very similar to the corresponding values for the unfolding of intact thioredoxin at 25 degrees C. However, both DeltaH0 and DeltaS are significantly more positive for dissociation of the complex, suggesting a decreased hydrophobic stabilization of the complex relative to the situation for intact thioredoxin.

Bacterial Proteins↗
PubMed1999

Kinetics of the interaction of endotoxin with polymyxin B and its analogs: a surface plasmon resonance analysis.

Lipopolysaccharide, the invariant structural component of Gram-negative bacteria, when present in minute amounts in the circulation in humans elicits 'endotoxic shock' syndrome, which is fatal in 60% of the cases. Polymyxin B (PMB), a cyclic cationic peptide, neutralizes the endotoxin, but also induces many harmful side effects. Many peptide-based drugs mimicking the activity of PMB have been synthesized in an attempt to reduce toxicity while still retaining the anti-endotoxic activity. The study attempts to use the recent technique of surface plasmon resonance (SPR), in determining the kinetics of association and dissociation involved in the interaction of endotoxin with a few selected peptides that have structural features resembling PMB. The results, in conjunction with the thermodynamic data derived using isothermal titration calorimetry (ITC), stress the vital role played by amphiphilicity of the peptides and hydrophobic forces in this biologically important interaction.

Kinetics↗
PubMed1999

Delayed pneumothorax and hydrothorax with central venous catheter migration.

We report a case of delayed pneumothorax, central venous catheter migration and iatrogenic hydrothorax in a 22-year-old female. The left subclavian central venous catheter initially transfixed the lung apex; pneumothorax occurred 24 h later following initiation of positive pressure ventilation. Lung collapse as a result of the pneumothorax caused catheter migration and hydrothorax. Catheter removal and chest drainage led to an uneventful recovery.

Adult↗
PubMed1999

Itraconazole prophylaxis for fungal infections in patients with advanced human immunodeficiency virus infection: randomized, placebo-controlled, double-blind study. National Institute of Allergy and Infectious Diseases Mycoses Study Group.

In a prospective, randomized, double-blind trial, 149 patients with advanced human immunodeficiency virus (HIV) infection were randomized to receive itraconazole capsules (200 mg daily) and 146 to receive a matched placebo. Both groups were monitored for evidence of fungal infections. Baseline characteristics of the two groups were similar. Failure of prophylaxis occurred in 29 (19%) of the itraconazole recipients and 42 (29%) of the placebo recipients (P = .004; log-rank test). There were 6 invasive fungal infections in the itraconazole group (4, histoplasmosis; 1, cryptococcosis; 1, aspergillosis) and 19 in the placebo group (10, histoplasmosis; 8, cryptococcosis; 1, aspergillosis) (P = .0007; log-rank test). Itraconazole significantly delayed time to onset of histoplasmosis (P = .03; log-rank test) and cryptococcosis (P = .0005; log-rank test). Prophylaxis failure due to recurrent or refractory mucosal candidiasis occurred with similar frequency in the two groups (itraconazole, 15%; placebo, 16%). A survival benefit was not demonstrated. Itraconazole generally was well tolerated. Primary prophylaxis with itraconazole capsules prevents histoplasmosis and cryptococcosis in patients with HIV infection.

AIDS-Related Opportunistic Infections↗
PubMed1999

Similar baroreflex bradycardic actions of atrial natriuretic peptide and B and C types of natriuretic peptides in conscious rats.

OBJECTIVE: We have previously shown that atrial natriuretic peptide (ANP) modulates cardiac barosensitive afferent pathways to enhance reflex bradycardia in rats. The present study examined whether B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) also modulate heart rate reflex function. DESIGN: Baroreflex bradycardia was evoked by rapid (over 4-6 s) intravenous (i.v.) infusions of methoxamine (100 microg/kg; 'ramp' baroreflex technique) in the presence of infused i.v. natriuretic peptide and of vehicle (0.9% saline, 270 microl/h) in conscious adult Munich-Wistar rats. Initially a dose-response study to ANP (infused at 25, 50 and 100 pmol/kg per min i.v.) was performed in 10 rats to determine an appropriate dose for subsequent experiments with the other peptides. In a separate group of 11 animals, rat BNP-32 and rat CNP-22 were infused at 50 pmol/kg per min i.v. RESULTS: Reflex responses to ANP were dose-related, with a significant increase in baroreflex sensitivity of 50+/-15% at the 25 pmol dose, 102+/-10% at the 50 pmol dose and 117+/-11% at 100 pmol dose (all P<0.05). BNP and CNP (50 pmol/kg/min i.v.) substantially increased baroreflex bradycardia (by 115+/-17% and 62+/-15%, respectively; P<0.05) compared to vehicle infusion. CONCLUSIONS: Both BNP and CNP augmented baroreflex slowing of heart rate in response to rapid increases in blood pressure in rats. Whereas other reports have shown marked differences in cardiovascular responses between the natriuretic peptides, particularly with CNP, our findings demonstrate an important common action of ANP, BNP and CNP to facilitate vagal heart rate baroreflexes.

Animals↗
PubMed1998

Induction of a spectroscopically defined transition by guanidinium hydrochloride on a recombinant calcium binding protein from Entamoeba histolytica.

Sequence analysis and metal ion binding studies reported earlier have established that the calcium binding protein (CaBP) from the parasitic ameboid Entamoeba histolytica protein has four canonical EF hand motifs which bind calcium. Equilibrium denaturation studies on both the apo and the holo forms of this protein indicate the presence of stable transition intermediates at low denaturant concentrations as revealed by the binding of the non-specific hydrophobic dye ANS. Fast reaction kinetics shows that the binding of the Gdn+ ions at or near the Ca2+ sites in the N-terminal domain influences metal ion binding to the sites in the C-terminal domain. Isothermal calorimetric titrations performed using low GdnHCl concentrations reveal the presence of two binding sites of low affinity, both being endothermic in nature. Thus the stabilization of CaBP observed at low GdnHCl concentration represents a native-like intermediate, with the Gdn+ ions mimicking Ca2+ binding at the N-terminal domain of this protein.

Animals↗
PubMed1998

Mapping the ranges and relative abundance of the two principal African malaria vectors, Anopheles gambiae sensu stricto and An. arabiensis, using climate data.

Members of the Anopheles gambiae complex are major malaria vectors in Africa. We tested the hypothesis that the range and relative abundance of the two major vectors in the complex, An. gambiae sensu stricto and An. arabiensis, could be defined by climate. Climate was characterized at mosquito survey sites by extracting data for each location from climate surfaces using a Geographical Information System. Annual precipitation, together with annual and wet season temperature, defined the ranges of both vectors and were used to map suitable climate zones. Using data from West Africa, we found that where the species were sympatric, An. gambiae s.s. predominated in saturated environments, and An. arabiensis was more common in sites subject to desiccation (r2 = 0.875, p < 0.001). We used the nonlinear equation that best described this relationship to map habitat suitability across Africa. This simple model predicted accurately the relative abundance of both vectors in Tanzania (rs = 0.745, p = 0.002), where species composition is highly variable. The combined maps of species' range and relative abundance showed very good agreement with published maps. This technique represents a new approach to mapping the distribution of malaria vectors over large areas and may facilitate species-specific vector control activities.

Animals↗