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N Unwin

Publications and source records attributed to N Unwin.

At least 55 records · Page 3Linked to original sources
PubMed1998

Macromolecular structure determination by electron microscopy: new advances and recent results.

Electron microscopy is undergoing a mini-renaissance, as a number of biological systems are yielding to higher resolution analysis as a result of advances in instrumentation, specimen preparation and image-processing technology. The atomic structure of tubulin has now been solved, crucial elements of secondary structure have recently been revealed in several membrane proteins (rhodopsin, gap junctions, aquaporin, and Ca2+ and H+ ATPases) and in a virus particle, and macromolecular complexes are being seen in increasingly fine detail. This growth has been enhanced further by the ability to combine structures of macromolecular complexes derived by electron microscopy with X-ray structures of their components, in order to reconstruct molecular machines and large multiprotein complexes in immense detail.

Crystallization↗
PubMed1997

Distortion correction of tubular crystals: improvements in the acetylcholine receptor structure.

Biological molecules often crystallize either as tubes, having helical symmetry, or as two-dimensional sheets. Both sorts of crystal are potentially suitable for structure determination to atomic resolution by electron crystallography, but their lattice distortions must first be corrected. We have developed a procedure for tubular crystals, based on independent alignment of very short segments against a reference structure, that allows accurate determination and correction of distortions in all three dimensions. Application of this procedure to images used previously to determine the 9 A structure of the acetylcholine receptor showed that about half of the signal loss caused by the distortions arises from effects correctable in the image plane (bending, changes in scale) and half from effects requiring out-of-plane correction (variations in tilt and in twist around the tube axis). By dividing the tubes into short segments (of lengths about equal to their diameter) it became possible to recover almost all of this loss without reducing appreciably the accuracy in the segmental alignments. The signal retention improved by only 10% at low resolution (20 A), but by progressively greater amounts at higher resolutions, up to approximately 40% at 9 A. As a result the finer structural details were more clearly resolved. With images of better electron-optical quality, much greater gains in signal retention should be obtained.

Animals↗
PubMed1997

Body mass index, waist circumference, waist-hip ratio, and glucose intolerance in Chinese and Europid adults in Newcastle, UK.

OBJECTIVE: To compare the prevalence of glucose intolerance (impaired glucose tolerance and diabetes), and its relationship to body mass index (BMI) and waist-hip ratio in Chinese and Europid adults. DESIGN: This was a cross sectional study. SETTING: Newcastle upon Tyne. SUBJECTS: These comprised Chinese and Europid men and women, aged 25-64 years, and resident in Newcastle upon Tyne, UK. MAIN OUTCOME MEASURES: Two hour post load plasma glucose concentration, BMI, waist circumference, and waist-hip ratio. METHODS: Population based samples of Chinese and European adults were recruited. Each subject had a standard WHO oral glucose tolerance test. RESULTS: Complete data were available for 375 Chinese and 610 Europid subjects. The age adjusted prevalences of glucose intolerance in Chinese and Europid men were 13.0% (p = 0.04). Mean BMIs were lower in Chinese men (23.8 v 26.1) and women (23.5 v 26.1) than in the Europids (p values < 0.001), as were waist circumferences (men, 83.3 cm v 90.8, p < 0.001; women, 77.3 cm v 79.2, p < 0.05). Mean waist-hip ratios were lower in Chinese men (0.90 v 0.91, p = 0.02) but higher in Chinese women (0.84 v 0.78, p < 0.001) compared with Europids. In both Chinese and Europid adults, higher BMI, waist circumference, and waist-hip ratio were associated with glucose intolerance. CONCLUSIONS: The prevalence of glucose intolerance in Chinese men and women, despite lower BMIs, is similar to or higher than that in local Europid men and women and intermediate between levels found in China and those in Mauritius. It is suggested that an increase in mean BMI to the levels in the Europid population will be associated with a substantial increase in glucose intolerance in Chinese people.

Adult↗
PubMed1997

Low levels of cardiovascular risk factors and coronary heart disease in a UK Chinese population.

OBJECTIVE: To compare the prevalence of cardiovascular risk factors and coronary heart disease in Chinese and Europid adults. DESIGN: Population based, cross sectional survey. SETTING: Newcastle upon Tyne, UK, 1991-93. SUBJECTS: Altogether 380 Chinese and 625 Europid adults, aged 25-64 years. MAIN OUTCOME MEASURES: Fasting lipid levels, blood pressure, body mass index (BMI), the proportions who smoked, and the prevalence of coronary heart disease based on the Rose angina questionnaire and major electrocardiographic abnormalities on resting 12 lead electrocardiogram (Minnesota codes 1.1-1.2). All figures were age adjusted to the 1991 England and Wales population. RESULTS: Altogether 183 and 197 Chinese, and 310 and 315 Europid men and women respectively were seen. Compared with Europid men, Chinese men had a lower mean total cholesterol concentration (5.1 versus 5.6 mmol/l, p < 0.001) and LDL cholesterol (3.2 versus 3.6 mmol/l, p < 0.001); lower BMI values (23.8 versus 26.1 kg/m-2, p < 0.001); and smoked less (23% versus 35%, p < 0.01)). Compared with Europid women, Chinese women also had lower mean lipid levels (total cholesterol: 4.9 versus 5.4 mmol/l p < 0.001, LDL cholesterol: 2.8 versus 3.1 mmol/l p < 0.001); BMI values (23.5 versus 26.1 kg/m-2, p < 0.001); and far fewer were smokers (1.4% versus 33%, p < 0.001). Chinese women, however, had higher mean systolic (121 versus 117 mmHg, p > 0.05) and diastolic (75 versus 68 mmHg, p < 0.001) blood pressures. The prevalence of coronary heart disease was significantly lower in Chinese than Europid men (4.9% versus 16.6%, p < 0.001) but not significantly different in women (7.3% versus 11.1%, p = 0.16). CONCLUSION: Strategies for UK Chinese are needed to maintain this favourable risk factor profile and prevent any potential increase in the risk of coronary heart disease associated with increasing acculturation.

Adult↗
PubMed1996

Projection structure of the nicotinic acetylcholine receptor: distinct conformations of the alpha subunits.

The nicotinic acetylcholine (ACh) receptor is a neurotransmitter-gated ion channel consisting of a ring of five membrane-spanning subunits, including two (the alpha subunits) with identical amino acid sequences. To open the channel ACh has to bind at two sites, involving both alpha subunits, which have widely different affinities. An earlier three-dimensional electron microscopic study of the non-activated Torpedo receptor had suggested that these sites might be cavities with the alpha subunits, located 25 to 30 A from the membrane, and hence that the different affinities might be associated with alternative conformations of the alpha subunits. This paper compares the conformations of the alpha subunits by determining the projection structure of the non-activated receptor and correlating the projection and three-dimensional maps. The projection structure was calculated to 7.5 A resolution from images of ice-embedded "giant" tubular crystals of Torpedo membranes, which had been partially flattened to make pairs of two-dimensional sheets (rho 2 lattice: a=90.2 A, beta=162.3 A, gamma=121.7 degrees). Each subunit in projection occupied a sector of approximately 72 degrees, and had a peak of high density at a distance of 22 to 25 A from the pseudo 5-fold axis. This peak in the single subunit between the alphas was approximately 3 A further from the axis than were the other peaks, and the projected density distributions composing the two alpha subunits were different. Close matching of the projected densities with the three-dimensional densities 25 to 35 A from the membrane, showed unequivocally that corresponding (alpha-helical) rods, which encircle the cavities in the two alpha subunits, are unequally inclined. Therefore, the cavities are indeed shaped by distinct conformations of the alpha subunits before ACh has bound. A model is proposed of how both alpha subunits participate concertedly to open the channel, assuming that ACh binds to these internal sites.

Animals↗
PubMed1996

Outlook for survivors of childhood in sub-Saharan Africa: adult mortality in Tanzania. Adult Morbidity and Mortality Project.

OBJECTIVE: To measure age and sex specific mortality in adults (15-59 years) in one urban and two rural areas of Tanzania. DESIGN: Reporting of all deaths occurring between 1 June 1992 and 31 May 1995. SETTING: Eight branches in Dar es Salaam (Tanzania's largest city), 59 villages in Morogoro rural district (a poor rural area), and 47 villages in Hai district (a more prosperous rural area). SUBJECTS: 40,304 adults in Dar es Salaam, 69,964 in Hai, 50,465 in Morogoro rural. MAIN OUTCOME MEASURES: Mortality and probability of death between 15 and 59 years of age (45Q15). RESULTS: During the three year observation period a total of 4929 deaths were recorded in adults aged 15-59 years in all areas. Crude mortalities ranged from 6.1/1000/year for women in Hai to 15.9/1000/year for men in Morogoro rural. Age specific mortalities were up to 43 times higher than rates in England and Wales. Rates were higher in men at all ages in the two rural areas except in the age group 25 to 29 years in Hai and 20 to 34 years in Morogoro rural. In Dar es Salaam rates in men were higher only in the 40 to 59 year age group. The probability of death before age 60 of a 15 year old man (45Q15) was 47% in Dar es Salaam, 37% in Hai, and 58% in Morogoro; for women these figures were 45%, 26%, and 48%, respectively. (The average 45Q15s for men and women in established market economies are 15% and 7%, respectively.) CONCLUSION: Survivors of childhood in Tanzania continue to show high rates of mortality throughout adult life. As the health of adults is essential for the wellbeing of young and old there is an urgent need to develop policies that deal with the causes of adult mortality.

Adolescent↗
PubMed1996

The relationships between cardiovascular risk factors and socio-economic status in people with diabetes.

The hypothesis that the prevalence of cardiovascular risk factors in people with diabetes is inversely related to socio-economic status was tested. Demographic and biochemical data were collected on 1246 patients, aged 20-69 years, attending a hospital diabetes clinic. This is estimated to represent between 71% and 78% of all people of this age with a diagnosis of diabetes in the health authority. In total, 296 people were classified as Type 1 (insulin-dependent) diabetic patients (age of onset < 31, now on insulin). Using data from the 1991 census a deprivation score was ascribed to each individual according to their area (enumeration district) of residence. The total study population was ranked by deprivation score and divided into quintiles. The relationships between means and quintiles of deprivation were assessed by ANOVA for linear trend, and between proportions and quintiles of deprivation by the chi-squared test for trend. In Type 1 diabetes increasing quintiles of deprivation were significantly related to mean serum cholesterol (p < 0.01) and proportion smoking (p < 0.01), and in Type 2 (non-insulin-dependent) diabetes to mean body mass index (p < 0.001), proportion smoking (p < 0.001), and proportion with proteinuria (p < 0.05). The need for health measures to prevent cardiovascular disease in people with diabetes is greatest in deprived areas.

Adult↗
PubMed1996

Are body mass or insulin resistance independently associated with cardiovascular risk factors in non-diabetic elderly Nigerians?

The aim was to establish whether risk factors for cardiovascular disease (CVD) are positively and independently associated with fasting insulin and/or body mass and waist-hip ratio in healthy elderly Nigerian subjects. Fasting plasma glucose, insulin, total cholesterol, triglycerides, blood pressure, and basal insulin resistance (HOMA method) were measured in 500 healthy elderly (> or = 55 years) Nigerian volunteers (295 men, 205 women). Associations between blood pressure, triglycerides or cholesterol and fasting insulin, HOMA, body mass index (BMI) or waist-hip ratio were examined using linear regression. Age was controlled for in all analyses. In men, diastolic and systolic blood pressure were strongly associated with BMI, while there was no evidence of an independent relationship with fasting insulin or HOMA. Triglycerides were strongly associated with waist-hip ratio, with a weaker independent association with HOMA but not fasting insulin; fasting insulin and HOMA showed strong independent associations with total cholesterol. In women diastolic and systolic blood pressure were also strongly associated with BMI, but there was an independent relationship with fasting insulin for diastolic blood pressure and a less significant (p = 0.057) one for systolic blood pressure. Triglycerides were significantly associated with BMI but none of the other variables; there were no significant associations with cholesterol. There was no evidence of interaction between fasting insulin or HOMA and BMI or waist-hip ratio. The results suggest the hypotheses that in this population BMI or waist-hip ratio are stronger determinants of blood pressure and triglyceride levels than fasting insulin or HOMA, and that where insulin does play a role its effects are separate and additive.

Age Factors↗
PubMed1996

Diabetes mellitus as a cause of death in sub-Saharan Africa: results of a community-based study in Tanzania. The Adult Morbidity and Mortality Project.

The aim of this study was to determine the contribution of diabetes mellitus to all-cause mortality and diabetes mortality rates in adults 15 years and above living in one urban and two rural areas of Tanzania (Dar es Salaam, Hai and Morogoro Rural Districts). The three surveillance populations comprised 307,912 persons. Prospective monitoring of all deaths between 1 June 1992 and 31 May 1995 was carried out. Cause of death was determined by verbal 'autopsy' conducted with relatives of the deceased. In total, 4299 deaths were recorded in children (aged < 15 years) and 8054 in adults. In children there were no reported deaths associated with diabetes (due to or in children with diabetes). The adult male mortality rates associated with diabetes were 34, 30, and 15 per 100,000 per year in Dar es Salaam, Hai and Morogoro Rural Districts respectively. The figures in women were 21, 18, and 4 per 100,000 per year, respectively. The percentages of all adult male deaths associated with diabetes were 2.6%, 2.1% and 0.7% respectively. In women the percentages were 1.7%, 1.8%, and 0.2% respectively. Acute metabolic complications, infection, and stroke each accounted for approximately 30% of all diabetic deaths. Thus diabetes mortality rates varied between the three surveillance areas, being lowest in the poorest rural area. Rates were higher in men in all areas. While care is required in the comparison of mortality rates between countries, it was noteworthy that Tanzania, a country with a low diabetes prevalence, had diabetes mortality rates which were higher than or comparable to rates in Mauritius and the United States. Most patients died from preventable causes, indicating a need for improved case-management of diabetic emergencies as well as better detection and treatment of hypertension.

Adolescent↗
PubMed1996

Agreement between the Takeda UA-731 automatic blood pressure measuring device and the manual mercury sphygmomanometer: an assessment under field conditions in Newcastle upon Tyne, UK.

STUDY OBJECTIVE: To assess agreement between two Takeda UA-731 automatic blood pressure measuring devices (referred to as machines A and B) and two manual mercury sphygmomanometers. DESIGN: A 'Y' connector attached each Takeda UA-731 to a manual mercury sphygmomanometer. Simultaneous measurements were made on adult subjects. SETTING: A population based cardiovascular disease survey in Newcastle upon Tyne, UK. PARTICIPANTS: Measurements on machine A were compared in 71 individuals (all women), and on machine B in 75 individuals (9 men, 66 women). The age range of subjects was 28 to 76 years and median ages were 59 years for machine A and 50 years for machine B. MAIN RESULTS: Blood pressure (mmHg) ranged from 72 to 212 systolic and 44 to 102 diastolic. Both Takedas gave significantly lower readings than the manual devices for systolic and diastolic pressures: differences were mean (SD: 95% CI) 3.7 mmHg (6.5: 2.2, 5.2) for machine A systolic, 2.3 mmHg (4.5: 1.3, 3.4) machine A diastolic; 1.8 mmHg (6.2: 0.4, 3.3) machine B systolic, and 1.8 (4.4: 0.8, 2.8) machine B diastolic. On the British Hypertension Society criteria, machine A was graded C on systolic measurements and B on diastolic; machine B was graded B on both systolic and diastolic measurements. CONCLUSIONS: The performance of these machines compares favourably with the Dinamap 8100, recently adopted for survey work by the Department of Health. The Takeda UA-731 looks promising for epidemiological survey work but before it can be fully recommended further evaluations are needed.

Adult↗
PubMed1995

Acetylcholine receptor channel imaged in the open state.

The structure of the open-channel form of the acetylcholine receptor has been determined from electron images of Torpedo ray postsynaptic membranes activated by brief (< 5 ms) mixing with droplets containing acetylcholine. Comparison with the closed-channel form shows that acetylcholine initiates small rotations of the subunits in the extracellular domain, which trigger a change in configuration of alpha-helices lining the membrane-spanning pore. The open pore tapers towards the intracellular membrane face, where it is shaped by a 'barrel' of alpha-helices having a pronounced right-handed twist.

Acetylcholine↗
PubMed1995

Three-dimensional location of the main immunogenic region of the acetylcholine receptor.

About two-thirds of the antibodies to the nicotinic acetylcholine (ACh) receptor in patients with the autoimmune disease myasthenia gravis bind to the main immunogenic region (MIR). This is small, well-defined region on each of the two alpha subunits, containing residues 67-76 (alpha 67-76). By determining the structure of the ACh receptor complexed with two different fragments of an MIR-directed antibody, we have determined the three-dimensional location of the MIR (and therefore residues alpha 67-76) to be at the extreme synaptic end of each alpha subunit. The antibody fragments extend from the binding site away from the receptor axis and into the synaptic cleft, minimizing any steric interference neighboring ACh receptors might have with their binding.

Animals↗
PubMed1994

Images of purified Shaker potassium channels.

BACKGROUND: Voltage-gated K+ channels play an important role in the control of neuronal excitability and synaptic plasticity. Their low abundance and extraordinary heterogeneity have rendered their purification from natural sources difficult. We have previously cloned a voltage-gated K(+)-channel gene, Shaker, from Drosophila. The Shaker K(+)-channel polypeptide resembles one of the four internal repeats of a Na(+)- or Ca(2+)-channel alpha subunit, suggesting that this example of a K+ channel contains four identical or homologous subunits. Similar K(+)-channel polypeptides have been characterized from mammals, other vertebrate and invertebrate species, and from plants. Electrophysiological studies of K+ channels expressed in Xenopus oocytes suggest that they are indeed tetramers, and heteromultimeric K+ channels have been found in the mammalian brain. Until now, however, no K+ channel, nor any other member of the superfamily of voltage-gated ion channels, has been characterized by electron microscopy or other structural analysis. RESULTS: We have purified Shaker K+ channels, expressed in insect Sf9 cells, to apparent homogeneity, and imaged them using the electron microscope. The physical dimensions of these molecules, as well as their biochemical characteristics, are consistent with a tetrameric subunit composition. Moreover, the Shaker channel revealed by negative staining has the appearance of a four-fold symmetric tetramer, with a large, central vestibule that presumably constitutes part of the pathway for ions. CONCLUSION: These first clear images of a voltage-gated ion channel reveal a marked four-fold symmetry. The integrity of the purified tetrameric complex indicates that the purification scheme used in this study may be further developed for future structural analysis of voltage-gated K+ channels.

Animals↗