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Biomedical subjects

A F Drake

Publications and source records attributed to A F Drake.

At least 19 recordsLinked to original sources
PubMed1997

Conformational properties of the prion octa-repeat and hydrophobic sequences.

We have used circular dichroism to study synthetic peptides from two important regions of the prion protein: the N-terminal octa-repeat domain and a highly conserved hydrophobic section. Our results show that the octa-repeat sequence in free solution can adopt a non-random, extended conformation with properties similar to the poly-L-proline type II left-handed helix. We also show that the conformation can be changed by temperature, organic solvents (e.g. acetonitrile) and on binding to phospholipid vesicles. We compared CD data from two peptides corresponding to the hydrophobic region between residues 106 and 136 which contained either methionine or valine at position 129. This variation represents a common polymorphism in humans which has been shown to influence predisposition towards iatrogenic and sporadic CJD. There was no detectable difference between the CD spectra of these peptides irrespective of the solvent conditions we used.

Amino Acid Sequence↗
PubMed1997

Structures, assays and receptors for locust adipokinetic hormones.

This review is concerned mainly with the adipokinetic hormones (AKHs) of locusts: their molecular conformations, actions and functions and the development of microfiltration assays in vitro. The physiological significance of having multiple hormones with overlapping actions whose efficacy changes during development is discussed in relation to the possibility that these reflect variations in populations of receptors and/or the pharmacokinetics of the peptides. The involvement of second messengers in the transduction mechanism of AKHs is reviewed, and we describe hormone-induced changes of intracellular calcium in single dispersed fat body cells. The structure activity relationships of the three locust AKHs and a number of analogues with variations at the N- and C-termini are discussed. A number of areas are identified where there are gaps in our understanding of these hormones, and some of these will be the focus of our future research.

Animals↗
PubMed1996

Fibromatosis colli: a common cause of neonatal torticollis.

In infants and children, cervical masses originate from a variety of pathologic, congenital and developmental conditions, and it is important to distinguish benign from serious lesions. Fibromatosis colli is a rare cervical lesion that typically presents in the neonatal period. It is the most common cause of neonatal torticollis and should be recognized by physicians caring for neonates and infants.

Fibroma↗
PubMed1996

Locusta-AKH-III and related peptides containing two tryptophan residues have unusual CD spectra.

Locusta adipokinetic hormone-III (AKH-III, < QLNFTPWWa) and three analogues have been studied by CD spectroscopy. The AKH peptides examined in which the tryptophan residues are adjacent present a distinctive negative-positive CD signature, in aqueous solution, that increases at low temperatures in ethanediol/water. In the presence of 0.6% SDS, a positive-minus CD is observed. The separation of the two tryptophan residues by an aliphatic amino acid results in a CD, in aqueous solution inverted from negative to positive CD at approximately 225nm. For the peptides with two adjacent tryptophan residues, the bisignate nature of this tryptophan-based CD at lower temperatures or in SDS indicates that the indole/indole orientation can adopt two limiting conformations. There is a correlation between the size of the negative CD at 225 nm and the AKH peptide potency which may indicate a preferred indole/indole orientation by the receptor.

Amino Acid Sequence↗
PubMed1996

Immunohistochemical localization of nitric oxide synthase activity in upper respiratory epithelium.

Nitric oxide (NO) production in the respiratory epithelium of the upper airways has recently been described. To better delineate the role of epithelial NO, the authors of this study attempted to identify the cell type responsible for the production of NO in rat tracheal epithelium and human nasal epithelium. They localized the activity of NO through immunohistochemical analysis with an antibody to L-citrulline, a marker for activity of the L-arginine-dependent nitric oxide synthase (NOS) pathway. Using anti-inducible NOS (iNOS) and anti-constitutive NOS (cNOS) antibodies, they also attempted to identify the specific NO isotypes that were present. The tracheal and nasal epithelium demonstrated strong immunoreactivity to citrulline in ciliated cells. The ciliated cells of the nasal turbinates demonstrated strong iNOS positivity, but no significant cNOS immunoreactivity. The study findings that iNOS activity is present in ciliated epithelial cells of rat and human upper respiratory epithelium suggest that NO may play a role in epithelial homeostasis and could potentially play a role in the pathogenesis of mucociliary dysfunction.

Animals↗
PubMed1996

The interaction between heparin and polylysine: a circular dichroism and molecular modelling study.

The sulfated polysaccharide heparin interacts with both poly-L- and poly-D-lysine, promoting the alpha-helix conformation in the polypeptide. Chemically modified heparins in which one of the three sulfate groups per disaccharide has been removed form the same type of complex with poly-L-lysine; when two of the three sulfate groups are removed this property is lost. Heparin oligosaccharides as small as the octasaccharide can still promote alpha-helix in poly-L-lysine; the hexa- and tetrasaccharides do not, but they do disturb to a lesser extent the dynamic conformation equilibrium associated with poly-L-lysine at pH7 (22 degrees C). A three-dimensional structure for the heparin/polylysine complex is proposed in which the helical heparin molecule and the alpha-helical polypeptide are side-by-side, not intertwining. The regular periodicity of sulfate group clusters along one side of the polysaccharide chain matches the periodicity of the polypeptide alpha-helix, allowing electrostatic interactions every three peptide turns between a heparin sulfate cluster and a zeta-amino group of the polylysine. The heparin octasaccharide is the smallest even-numbered oligosaccharide long enough for two such interactions to take place.

Circular Dichroism↗
PubMed1995

Circular-dichroism and fluorescence studies on melittin: effects of C-terminal modifications on tetramer formation and binding to phospholipid vesicles.

Studies were performed on a series of melittin analogues with selective alterations to the positively charged amino acid sequence at the C-terminus. Fluorescence studies were undertaken using the sole tryptophan residue in the analogues as an intrinsic fluorescence probe for indications of tetramer formation in free solution, and binding and insertion of the melittins into phospholipid bilayers. Studies were performed under conditions of low-salt buffer with increasing concentrations of phosphate added to promote self-association of the melittin monomers, and also in the presence of phospholipid vesicles. C.d. studies were also performed under conditions of increasing phosphate concentrations and in the presence of lipid vesicles to monitor the alpha-helical content of the melittins. It was found that selective replacement of the C-terminal basic amino acids by glutamine has different effects on self-association, alpha-helix formation and lipid binding of melittin.

Amino Acid Sequence↗
PubMed1995

Two new otolaryngologic findings in child abuse.

We reviewed cases of early childhood hoarseness caused by vocal nodules and functional hearing loss as being possible manifestations of child abuse. This is a retrospective review set in two urban referral centers. The patients consisted of four children with vocal nodules and known histories of abuse, and four children with functional hearing loss and histories suggestive of abuse. Vocal nodules or functional hearing loss may be indicators of an abusive situation. Child abuse should be considered in the differential diagnosis of these problems.

Adolescent↗
PubMed1995

The importance of extended conformations and, in particular, the PII conformation for the molecular recognition of peptides.

Crystallographic, isotopic labeling nmr and transferred nuclear Overhauser effect studies have highlighted the extended conformation as a very important element of secondary structure at the binding site of many peptide/protein complexes including peptide inhibitors-enzymes, B-cell epitopes-antibodies, and T-cell epitopes-major histocompatibility complex (MHC) of class I and II complexes. This paper discusses the peptide ligand conformation consequences of these findings particularly in view of the identification of the PII conformation (left-handed extended polyproline II) in free solution.

Amino Acid Sequence↗
PubMed1995

Monitoring nasal and oral airway patency.

The hypothesis that upper airway breathing behaviors generally follow the rules of a physiologic regulating system implies the existence of sensors that monitor the airway environment. The purpose of this study was to assess the sensitivity of the monitoring system to sudden changes in airway patency in healthy, adult subjects. An instrument capable of changing airway dimensions in about 10 ms was used to assess psychophysical recognition and physiologic responses to sudden changes in airway size. Our results indicate that psychophysical recognition of change in patency occurred at a mean constriction area of 0.31 cm2. These findings suggest that recognition of change in airway size occurs well before the airway becomes flow-limiting or severely obstructed.

Adult↗
PubMed1995

Effect of Lactobacillus acidophilus on antibiotic-associated gastrointestinal morbidity: a prospective randomized trial.

Oral antibiotic therapy can alter the gastrointestinal microflora and result in troublesome gastrointestinal complaints. Patients who have experience with broad-spectrum antibiotics may be reluctant to start or to comply with antibiotic therapy due to the associated discomfort. In the field of otolaryngology, oral antibiotic therapy is commonplace, and patient intolerance of a particular antibiotic may result in compromise to a less effective choice. Yogurt, which contains Lactobacillus acidophilus, is often recommended by practitioners to help reduce the side effects of oral antibiotic therapy. We wanted to objectively evaluate the effect of orally administered L. acidophilus on the gastrointestinal side effects of oral broad-spectrum antibiotic therapy. Twenty-seven outpatients, 10 years of age or older, with ear, sinus, or throat infections, in whom amoxicillin/clavulanate was felt to be the antibiotic of choice, were randomly assigned to amoxicillin/clavulanate only, or amoxicillin/clavulanate and Lactobacillus treatment groups. Each patient was advised by the nursing staff to consume a well-balanced diet, and a detailed explanation of the medication schedule was given. A questionnaire was given to each patient at the conclusion of therapy. The data were analyzed using Spearman's rank-order correlations. Concomitant therapy of L. acidophilus with amoxicillin/clavulanate was associated with a significant decrease in patient complaints of gastrointestinal side effects and yeast superinfection. Almost all patients (89%) reported resolution of infection during the course of therapy. We believe that use of L. acidophilus is warranted in patients on broad-spectrum antibiotic therapy with gastrointestinal complaints.

Adolescent↗
PubMed1995

Structure-activity relationships and physico-chemical properties of synthetic lipopeptide inhibitors of PKC.

Four synthetic lipopeptides, (K-pm 19,31), (K-pm 19,21,31), (K-pm 19,28,31) and (K-pm 19,21,28,31) with the lysine-palmitoyl (K-pm) residue as a lipophilic moiety, based on the pseudosubstrate sequence 19RFARKGALRQKNV31 (R19-V31), were found to be potent protein kinase C (PKC) inhibitors. However, the lipopeptides (K-pm 19,21,31), (K-pm 19,28,31) and (K-pm 19,21,28,31) were also found to act as protein kinase cAMP-dependent (PKA) inhibitors. Peptide (K-pm 19,31), the least water soluble, is marginally selective towards PKC, unlike the other palmitoyl derivatives studied here. Since the non-palmitoylated analogues (K 19,31), (K-ac 19,31), (K 19,21,31) and (K-ac 19,21,31) were inhibitors of PKC but not of PKA, the palmitoyl moiety must play a role in the specificity of protein kinase inhibition. In vitro, the lipophilic peptides showed greater stability to protease-mediated hydrolysis than the pseudosubstrate peptide depending upon the number of lipophilic (K-pm) residues. CD studies showed that in comparison with the peptide analogues, the remarkable resistance of the pseudosubstrate (R19-V31) to adopt an alpha-helix conformation in TFE, known to be strongly alpha-helix inducing, rules out this structure as the peptide binding conformation to PKC. By contrast, in aqueous media all the peptides show an extended conformation that correlates well with their inhibitory activity. This is in compliance with the crystallographic observation that an extended structure has been observed for the (5-24) PKI peptide inhibitor bound to PKA.

Circular Dichroism↗
PubMed1994

Correlations between biological activities and conformational properties for human, salmon, eel, porcine calcitonins and Elcatonin elucidated by CD spectroscopy.

Calcitonin (CT) inhibits osteoclastic bone resorption and induces calcium uptake from body fluids. A comparative study of the conformational behaviours of therapeutic calcitonins [salmon (s), eel (e), a synthetic eel calcitonin analogue (Elcatonin), porcine (p) and human (h) calcitonins] as a function of solvent polarity and temperature have been performed by circular dichroism spectroscopy. Elements of secondary structure were lacking in H2O but could be observed in 2,2,2-trifluoroethanol and sodium dodecyl sulphate. In particular, similar amounts of alpha-helical content (four alpha-helical turns) were estimated in trifluoroethanol despite the considerable differences in amino acid sequences. The relative ability to form an alpha helix, assessed by trifluoroethanol/H2O titration, was found to be Elcatonin > sCT > pCT > eCT > hCT. In Elcatonin, sCT, pCT and eCT the four alpha-helical turns were promoted almost completely in a single step, between 0 and 35% trifluoroethanol, unlike hCT where helical structure formation has been reported to involve two steps over the whole trifluoroethanol/H2O range [Arvinte, T. & Drake, A. F. (1993) J. Biol. Chem. 268, 6408-6414]. In SDS, which mimics the membrane environment, conformational differences (3-4 helical turns in Elcatonin, sCT, eCT versus one helical turn in pCT, hCT) were observed and correlate well with biological activity (Elcatonin = sCT = eCT > pCT = hCT). Low-temperature studies in a cryogenic solvent mixture showed the formation of high alpha-helix content (similar to that in trifluoroethanol) in Elcatonin, sCT, eCT and pCT, whilst a left-handed extended helix (3(1) helix) was formed in hCT. This is consistent with the hypothesis of 'linear' and 'helical' calcitonin receptors [Nakanuta, H., Orlowski, R. C. & Epand, R. M. (1990) Endocrinology 127, 163-169].

Amino Acid Sequence↗
PubMed1994

The effect of variation of substitution on the solution conformation of heparin: a spectroscopic and molecular modelling study.

The effect of variations in substitution on the conformation of iduronate-containing sequences in heparin and heparan sulphate has been studied using a series of chemically-modified heparins in which substitution with O- and N-sulphate and N-acetyl substituents has been systematically altered. Monosaccharides corresponding to residues in these modified heparins have also been investigated. The conformations of the glycosidic linkages in O- and N-desulphated re-N-acetylated heparin, O-desulphated re-N-sulphated heparin, and 6-O-desulphated re-N-sulphated heparin have been compared with those of N-desulphated re-N-acetylated heparin and of heparin itself, which have been compared with those of N-desulphated re-N-acetylated heparin and of heparin itself, which have previously been reported [B. Mulloy, M.J. Forster, C. Jones, and D.B. Davies, Biochem. J., 293 (1993) 849-858]. The overall conformation of all the polysaccharides is shown to be similar, regardless of substitution pattern. The conformational equilibrium of the pyranose ring of iduronic acid residues in the polysaccharides has been monitored by the use of 13C NMR chemical shift temperature coefficients, and shown to be similar for all the modified heparins with the exception of N-desulphated re-N-acetylated heparin. Circular dichroism spectra of all the polysaccharides are reported, and their variations attributed to differences in the proportions of pyranose ring forms in the iduronate conformational equilibrium.

Carbohydrate Conformation↗