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Biomedical subjects

R A Scott

Publications and source records attributed to R A Scott.

At least 73 records · Page 4Linked to original sources
PubMed1997

Dissecting contributions to the thermostability of Pyrococcus furiosus rubredoxin: beta-sheet chimeras.

The contributions to thermostability of interactions within the beta-sheet region of rubredoxins (Rds) were investigated by examining proteins in which beta-strand sequences of Rds from the hyperthermophilic archaeon Pyrococcus furiosus (Pf) and the mesophilic bacterium Clostridium pasteurianum (Cp) were interchanged. The thermostabilities of the chimeric Rds were assessed by monitoring the decay of the visible absorbance at 490 nm and of the far-UV CD vs time at 92 degrees C. The chimeric Rds Pf15 Cp47 Pf (Pf Rd residues 2-15 and 48-54 and Cp Rd residues 16-47) and Cp15 Pf47 Cp were both found to be far less thermostable than wild-type Pf Rd, indicating that neither the beta-sheet residues (2-7, 10-15, and 48-53) nor the "core residues" (16-47) of Pf Rd independently confer Pf Rd-like thermostability. However, the chimeric Rd Pf47 Cp exhibits thermostability close to that of wild-type Pf Rd, suggesting that Pf Rd-like thermostability is conferred by interactions of beta-sheet strands 1 and 2 (residues 2-15) together with Pf core residues. In contrast, Cp Rd beta-sheet strands 1 and 2 connecting to Pf Rd core residues are thermodestabilizing in the chimera Cp15 Pf Rd. These results suggest that a global alignment which optimizes both main chain and side chain interactions between beta-sheet strands and core residues is more important than a few localized interactions within the beta-sheet in conferring Pf Rd-like thermostability.

Amino Acid Sequence↗
PubMed1997

Bifurcated stent-graft for abdominal aortic aneurysm.

The purpose of this study was to examine bifurcated stent-graft implantation for abdominal aortic aneurysm. Fifty-seven patients were treated and followed with serial computed tomography scans for up to 3 years. Patients were allocated to three groups (first 20, second 20, last 17) according to when the repair was performed. Successful treatment is defined as exclusion of the aneurysm from the circulation, based on contrast computed tomography. Success rates in the three groups were 55%, 70% and 100%. Perigraft leak (endoleak) was present on initial assessment in 4/20, 2/20 and 1/17. Two of these aneurysms ruptured early in the postoperative period. Thereafter, leaks were sought and treated aggressively. Kinking and thrombosis occurred in six of the first 20 patients, but did not occur in any of the last 37 patients, in whom the graft limbs were routinely stent-supported throughout. Infrarenal implantation in very a short neck (< 10 mm), or a thrombus-lined neck was associated with proximal stent migration. In conclusion, changes in patient selection and technique have led to a steady rise in the short-term success rate of the stent-grafted implantation.

Aneurysm, Ruptured↗
PubMed1997

E-cadherin distribution and epithelial basement membrane characteristics of the normal human conjunctiva and cornea.

The conjunctival mucosa has several similarities to the mucosal immune system of the gut and bronchus. Like the gut and bronchial mucosa, the conjunctiva is capable of inducing tolerance to encountered antigens and possesses a repertoire of CD8+ intraepithelial lymphocytes (IELs) bearing the human mucosal lymphocyte-1 antigen (HML-1) which has been shown to be an alpha E beta 7 integrin. The epithelial cells surface ligand for HML-1 is E-cadherin. The distribution of E-cadherin in the normal human conjunctiva and cornea is not known. We investigated E-cadherin distribution in the conjunctiva and cornea by immunohistochemistry. E-cadherin was found to be present in all layers of the conjunctival epithelium but not in corneal epithelium. In the conjunctiva it may act as a ligand for the HML-1+ IELs. The specific location of IELs along the basal cells of the conjunctiva compared with the generalised distribution of E-cadherin through all layers, indicates that factors other than E-cadherin binding determine the distribution of HML-1+ IELs. We performed electron microscopy on de-epithelialised conjunctival and corneal samples. We demonstrated the presence of epithelial basement membrane pores in the conjunctiva but not in the cornea. Lymphocyte migration from the substantia propria to the intraepithelial compartment appears to occur through these pores, which may also serve as a conduit for antigen presentation by epithelial antigen presenting cells (APCs) to lymphocytes in the substantia propria.

Aged↗
PubMed1997

European experience with a system for bifurcated stent-graft insertion.

PURPOSE: To test an endovascular aneurysm exclusion system in the presence of a wide range of challenging anatomic features. METHODS: Bifurcated endovascular stent-grafts were inserted in 52 patients and followed with serial computed tomography for up to 3 years. The device underwent several modifications during this time, the most significant of which represent the difference between the homemade (n = 42) and industry-made (n = 10) versions. RESULTS: The initial procedural success rate was 92% in the homemade group and 100% in the industry-made group. In the 3 years of follow-up, the long-term success rate was 64% in the homemade group and 90% in the industry-made group. The primary reasons for failure in the homemade group were graft thrombosis due to kinking early in the series and proximal stent migration later in our experience. All cases of migration occurred when the neck was < 15 mm in length, the neck was lined with thrombus, or the stent was implanted > 15 mm from the renal arteries. Kinking was subsequently overcome by implanting Wallstents throughout the graft limbs. The sole failure in the industry-made group was a case in which collateral perfusion reached the aneurysm through patent lumbar arteries. CONCLUSIONS: The fruits of this experience are a better technique, a better device, and, most importantly, a better understanding of the system's limits, as reflected in the current selection criteria.

Angiography↗
PubMed1996

Characterization of the mononickel metallocenter in H134A mutant urease.

A mutant form of Klebsiella aerogenes urease possessing Ala instead of His at position 134 (H134A) is inactive and binds approximately half the normal complement of nickel (Park, I.-S., and Hausinger, R. P.(1993) Protein Sci. 2, 1034-1041). The crystal structure of the H134A protein was obtained at 2.0-A resolution, and it confirms that only Ni-1 of the two nickel ions found in the native enzyme is present. In contrast to the pseudotetrahedral geometry observed for Ni-1 in native urease (where it is liganded by His-246, His-272, one oxygen atom of carbamylated Lys-217, and a water molecule at partial occupancy), the mononickel metallocenter in the H134A protein was found to possess octahedral geometry and was coordinated by the above protein ligands plus three water molecules. The nickel site of H134A urease was probed by UV-visible, variable temperature magnetic circular dichroism, and x-ray absorption spectroscopies. The spectroscopic data are consistent with the presence of Ni(II) in octahedral geometry coordinated by two histidylimidazoles and additional oxygen and/or nitrogen donors. These data underscore the requirement of Ni-2 for formation of active urease and demonstrate the important role of Ni-2 in establishing the proper Ni-1 coordination geometry.

Binding Sites↗
PubMed1996

The role of arsenic-thiol interactions in metalloregulation of the ars operon.

The ars operon of the Escherichia coli plasmid R773 that confers arsenical and antimonial resistance is negatively regulated by the ArsR repressor. ArsR residues Cys-32 and Cys-34 were previously identified as involved in induction by arsenite and antimonite, suggesting coordination between As(III) and the two cysteine thiolates. However, in small molecule thiolate-As(III) complexes, arsenic is frequently three-coordinate. A site-directed mutagenic approach was employed in a search for a third arsenic ligand. ArsR proteins with C32G, C34G, and C32G/C34G substitutions were active repressors, but were not inducible in vivo. In vitro, the altered repressor-ars DNA complexes could not be dissociated by inducers. Alteration of Cys-37 and Ser-43, residues located in or near the putative helix-turn-helix DNA-binding region of the protein, had no effect on the inducibility of the operon. While these results indicated that neither the thiolate of Cys-37 nor the hydroxyl oxygen of Ser-43 is required for induction, they did not eliminate either atom as a potential arsenic ligand. Another approach involved reaction with an alternative inducer, phenylarsine oxide, which can form only two coordinations. Phenylarsine oxide was shown to be as effective as or more effective than arsenite or antimonite in induction in vivo. In vitro, the organic arsenical was more effective than either arsenite or antimonite in dissociating the repressor-promoter complex. Thus, two ArsR-arsenic bonds are sufficient for induction. The interaction of ArsR proteins with As(III) was examined using a phenylarsine oxide affinity resin. ArsR proteins containing any two of the three cysteine residues Cys-32, Cys-34, and Cys-37 bound to the resin. Alteration of any two of the three resulted in loss of binding. Arsenic X-ray absorption spectroscopy of ArsR treated stoichiometrically with arsenite confirmed the average arsenic coordination as AsS3 These results suggest that all three cysteine thiolates are arsenic ligands, but binding to only two, the Cys-32 and Cys-34 thiolates, is required to produce the conformational change that results in release of the repressor from the DNA and induction.

Amino Acid Sequence↗
PubMed1996

Clinical experience with a bifurcated endovascular graft for abdominal aortic aneurysm repair.

PURPOSE: The purpose of this study was to test a transfemoral system of bifurcated endovascular graft insertion for aortic aneurysm repair. METHODS: Bifurcated endovascular grafts were inserted through bilateral femoral artery cutdowns in 41 patients. The results were assessed by completion angiography and follow-up computed tomography. RESULTS: The second half of the study included more aneurysms 6 cm or larger (p < 0.05) and more instances of short proximal neck (p < 0.05), proximal neck angulation (p < 0.05), and iliac angulation (p < 0.05). Despite the increasingly challenging anatomy, the results were better in the second half of the study as illustrated by the lower overall combined morbidity/mortality rate (15% vs 50%) and higher overall success rate (85% versus 65%). The mortality rate for the series as a whole was 7.5%. Mean follow-up was 18.8 months for the first 20 patients and 10.9 months for the second 20. The commonest complication in the first half of the study was graft thrombosis (n = 5). This complication was absent from the second half of the study because of routine adjunctive stenting. Two patients died of complications of endovascular repair. In both cases aneurysm rupture on the third postoperative day was associated with coagulopathy and angiographic signs of perigraft leak. CONCLUSION: Aneurysm exclusion with a bifurcated endovascular graft was feasible in a wide range of patients, but when the aneurysm was not entirely excluded from the circulation, the risk of rupture persisted.

Aorta, Abdominal↗
PubMed1996

Measurement-induced improvement in anxiety: mean shifts with repeated assessment.

Some personality test scores improve on retest. Three studies investigated the role of meaning change in producing this phenomenon. In Study 1 multiple versions of a Manifest Anxiety Scale were administered, with counterbalanced item orders. It was found that measurement-induced improvement (a) occurred within a test as well as between test and retest, (b) was unaffected by participants' anxiety scores, and (c) occurred even when the retest contained different items than the first test. Studies 2 and 3 found that as respondents experience more of a test, they are better able to discern its meaning and to use that meaning to interpret an item. These findings indicate that mean shifts in answers from test to retest also occur within a test along with context-induced shifts in meaning.

Anxiety Disorders↗
PubMed1996

Co-morbidity in patients with abdominal aortic aneurysm.

OBJECTIVES: Selection for surgery of patients with abdominal aortic aneurysm (AAA) depends on an assessment of risk from operation compared with risk from aneurysm rupture. A study was performed to assess the levels of co-morbidity and to see whether co-morbidity was different in people with a normal aorta after ultrasonographic examination than in those with an aneurysmal aorta. SETTING AND METHODS: Over a two year period 5392 people (2341 men, 3051 women) aged 65-80 were screened using B-mode linear ultrasound, with maximum measurements taken of transverse, anteroposterior diameters, or both. All subjects were given a questionnaire seeking a history of angina, stroke, claudication, myocardial infarct, respiratory problems, and diabetes. RESULTS: 218 men and women were found to have an AAA of 3 cm or greater. The results of the questionnaire were analysed using logistic regression whereby all the co-morbid conditions were adjusted for each other and for smoking, sex, and age. The only conditions which were significantly associated with AAA in both sexes were myocardial infarction with an odds ratio (OR) of 1.66 (95% confidence interval (CI) 1.06 to 2.60) and claudication with an OR of 1.68 (95% CI 1.17 to 2.42). The association between angina and AAA was of borderline significance (OR = 1.52, 95% CI 1.00 to 2.30). Stroke was significantly associated only in women, with an OR of 3.71 (95% CI 1.42 to 9.69). Rates of diabetes and respiratory disease were not significantly different between people with AAA and normal aortas. CONCLUSIONS: These findings show there is significantly higher co-morbidity in people with ultrasound detected AAA, which might influence outcome from surgery and long term survival.

Adult↗
PubMed1995

An X-ray absorption spectroscopy study of the interactions of Ni2+ with yeast enolase.

An x-ray absorption spectroscopy (XAS) study was carried out at pH 7.6 on solutions of Ni2+ and yeast enolase depleted of its physiological cofactor (Mg2+) in the presence or absence of substrate/product, the very strongly bound competitive inhibitor 2-phosphonoacetohydroxamate and Mg2+. Both "conformational" and "catalytic" Ni2+ are distorted octahedral in coordination, in agreement with several spectroscopic studies but in contrast to the coordination in the crystal at pH 6.0. The data are consistent with direct coordination of what must be the catalytic Ni2+ to the phosphate of the substrate, in agreement with some previous data but in disagreement with recent interpretations by other workers. The ligands around the metal ions obtained from the x-ray structure give simulated XAS spectra in good agreement with the observed spectra.

Binding Sites↗
PubMed1995

Discriminating compact nonnative structures from the native structure of globular proteins.

Prediction of the native tertiary structure of a globular protein from the primary sequence will require a potential energy model that can discriminate all nonnative structures from the native structure(s). A successful model must distinguish not only alternate structures that are very nonnative but also alternate structures that are compact and near-native. We describe here a method, based on molecular dynamics simulation, that allows generation of hundreds of compact alternate structures that are arbitrarily close to the native structure. In this way, a significant amount of conformational space in the neighborhood of the native structure can be sampled and these alternate structures can be used as a stringent test of protein folding models. We have used two sets of these alternate structures generated for six crystallographically characterized small globular proteins (1200 alternate structures in all) to test eight empirical energy models for their ability to discriminate alternate from native structures. Seven of the models fail to correctly identify at least some of the alternate structures as nonnative. An atomic solvation model is presented that succeeds in discriminating all 1200 alternate structures from native.

Amino Acid Sequence↗
PubMed1995

Influence of screening on the incidence of ruptured abdominal aortic aneurysm: 5-year results of a randomized controlled study.

From family medical practices 15775 men and women aged 65-80 years were identified and randomized into two groups: one group was invited for ultrasonographic screening for abdominal aortic aneurysm (AAA), and the other acted as age- and sex-matched controls. Of the 7887 invited for screening 5394 (68.4 per cent) accepted. AAA was detected in 218 (4.0 per cent overall and 7.6 per cent of men). Aortic surgery was offered to the screened group if certain criteria were met and no patient died from rupture who was fit for operation and accepted elective treatment. The incidence of rupture was reduced by 55 per cent in men in the group invited for screening, compared with controls. The incidence of rupture in women was low in both groups.

Age Factors↗
PubMed1995

A new computational model for protein folding based on atomic solvation.

A new model for calculating the solvation energy of proteins is developed and tested for its ability to identify the native conformation as the global energy minimum among a group of thousands of computationally generated compact non-native conformations for a series of globular proteins. In the model (called the WZS model), solvation preferences for a set of 17 chemically derived molecular fragments of the 20 amino acids are learned by a training algorithm based on maximizing the solvation energy difference between native and non-native conformations for a training set of proteins. The performance of the WZS model confirms the success of this learning approach; the WZS model misrecognizes (as more stable than native) only 7 of 8,200 non-native structures. Possible applications of this model to the prediction of protein structure from sequence are discussed.

Algorithms↗