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Biomedical subjects

B Rasmussen

Publications and source records attributed to B Rasmussen.

At least 37 records · Page 2Linked to original sources
PubMed1997

Crystal structure analysis of the activation of histidine by Thermus thermophilus histidyl-tRNA synthetase.

The crystal structure at 2.7 A resolution of histidyl-tRNA synthetase (HisRS) from Thermus thermophilus in complex with its amino acid substrate histidine has been determined. In the crystal asymmetric unit there are two homodimers, each subunit containing 421 amino acid residues. Each monomer of the enzyme consists of three domains: (1) an N-terminal catalytic domain containing a six-stranded antiparallel beta-sheet and the three motifs common to all class II aminoacyl-tRNA synthetases, (2) a 90-residue C-terminal alpha/beta domain which is common to most class IIa synthetases and is probably involved in recognizing the anticodon stem-loop of tRNA(His), and (3) a HisRS-specific alpha-helical domain inserted into the catalytic domain, between motifs II and III. The position of the insertion domain above the catalytic site suggests that it could clamp onto the acceptor stem of the tRNA during aminoacylation. Two HisRS-specific peptides, 259-RGLDYY and 285-GGRYDG, are intimately involved in forming the binding site for the histidine, a molecule of which is found in the active site of each monomer. The structure of HisRS in complex with histidyl adenylate, produced enzymatically in the crystal, has been determined at 3.2 A resolution. This structure shows that the HisRS-specific Arg-259 interacts directly with the alpha-phosphate of the adenylate on the opposite side to the usual conserved motif 2 arginine. Arg-259 thus substitutes for the divalent cation observed in seryl-tRNA synthetase and plays a crucial catalytic role in the mechanism of histidine activation.

Amino Acid Sequence↗
PubMed1997

Preoperative metoprolol improves cardiovascular stability and reduces oxygen consumption after thoracotomy.

BACKGROUND: Increased sympathetic activity perioperatively and associated cardiovascular effects play a central role in cardiovascular complications. High thoracic epidural blockade attenuates the sympathetic response, but even with complete pain relief, haemodynamic and endocrine responses are still present. Beta-adrenoceptor blockade is effective in situations with increased sympathetic activity. This study was designed to evaluate the perioperative haemodynamic effect of preoperative beta-blockade and its influence on the haemodynamic aspects of the surgical stress response. METHODS: Thirty-six otherwise healthy patients undergoing elective thoracotomy for lung resection were randomised double-blinded to receive either 100 mg metoprolol or placebo preoperatively. Anaesthesia was combined high thoracic epidural block and general anaesthesia. The epidural analgesia was continued during recovery. Patients were monitored with ECG, pulse oximetry, invasive haemodynamic monitoring, arterial blood gases and electrolytes. RESULTS: After induction of anaesthesia the mean arterial pressure (MAP) decreased in both groups, and decreased further in the placebo group after initiation of the epidural block. The heart rate (HR) was slightly less throughout the observation period after metoprolol. Peroperatively, the only difference in measured haemodynamics was a marginally higher MAP after metoprolol. Postoperative cardiac index (CI) was lower with a lower variability and cardiac filling pressures were slightly higher in the metoprolol group. The oxygen consumption index was higher after placebo throughout the observation period, with no difference in the oxygen delivery. CONCLUSION: We found that preoperative beta-blockade during combined general anaesthesia and high thoracic epidural blockade stabilised perioperative HR and CI and decreased total oxygen consumption.

Adrenergic beta-Antagonists↗
PubMed1996

Intracellular signaling for inducible antigen receptor-mediated Fas resistance in B cells.

CD40 ligand-activated B cells are sensitive targets for CD4+ Th1 effector cells that kill in a Fas-dependent fashion. Susceptibility to apoptosis is counteracted by Ag receptor binding that produces a state of resistance to Fas engagement in otherwise sensitive targets. In the present study, protection from Th1-mediated apoptosis was found to be induced by protein kinase C and calcium signals, which in combination mimicked the level of Fas resistance produced by surface Ig engagement. Signaling for Fas resistance did not alter Fas expression. Furthermore, B cells that were protected against Th1-mediated apoptosis were also resistant to apoptosis mediated by soluble, rFas ligand. Taken together, these results indicate that signaling for protection against Fas-mediated apoptosis does not depend on alteration of the interaction between B cell target and Th1 effector populations. Instead, surface IgM-derived protein kinase C and calcium signals appear to produce an intracellular change in the Fas signaling pathway that develops over a period of hours and interferes with the apoptotic process through a mechanism that depends on protein synthesis.

Animals↗
PubMed1996

How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 A resolution.

BACKGROUND: The enzyme methylmalonyl-coenzyme A (CoA) mutase, an alphabeta heterodimer of 150 kDa, is a member of a class of enzymes that uses coenzyme B12 (adenosylcobalamin) as a cofactor. The enzyme induces the formation of an adenosyl radical from the cofactor. This radical then initiates a free-radical rearrangement of its substrate, succinyl-CoA, to methylmalonyl-CoA. RESULTS: Reported here is the crystal structure at 2 A resolution of methylmalonyl-CoA mutase from Propionibacterium shermanii in complex with coenzyme B12 and with the partial substrate desulpho-CoA (lacking the succinyl group and the sulphur atom of the substrate). The coenzyme is bound by a domain which shares a similar fold to those of flavodoxin and the B12-binding domain of methylcobalamin-dependent methionine synthase. The cobalt atom is coordinated, via a long bond, to a histidine from the protein. The partial substrate is bound along the axis of a (beta/alpha)8 TIM barrel domain. CONCLUSIONS: The histidine-cobalt distance is very long (2.5 A compared with 1.95-2.2 A in free cobalamins), suggesting that the enzyme positions the histidine in order to weaken the metal-carbon bond of the cofactor and favour the formation of the initial radical species. The active site is deeply buried, and the only access to it is through a narrow tunnel along the axis of the TIM barrel domain.

Binding Sites↗
PubMed1996

Mortality and worsening of prognostic profile during waiting time for valve replacement in aortic stenosis.

In a prospective study 99 consecutive patients with operative indication due to severe aortic stenosis (AS) were put on a surgical waiting list. The waiting-time to aortic valve replacement (AVR) averaged 6.3 months (0.5-19 months). There were 58 men and 41 women with a mean age of 61 years (21-82 years). The patients were divided into three groups: group I (n = 81) with an uneventful stay on the waiting list (including one patient who declined the AVR offer); group II (n = 11) with significant worsening of a prognostic index; and group III (n = 7) with patients who died during the waiting-time. The waiting-list death rate was 13.5 +/- 5.0% patient-year-1 compared with a post-AVR death rate of 4.9 +/- 0.9%. patient-year-1 (p < 0.05) with a mean post-AVR follow-up of 5.7 years. According to their prognostic index at inclusion, group II patients had a predicted (by a Cox model) 7-year post-AVR survival probability of 72%, but only of 61% according to their prognostic index immediately preoperatively; their observed 7-year post-AVR survival was 60%. Logistic regression analysis identified high age, short duration of symptoms, severe hypertrophy and strain in the ECG, female sex, and deranged left-ventricular diastolic function (related to severely increased left-ventricular muscle mass) as independent predictors of death on the waiting-list and prognosis worsening. From a clinical viewpoint, the predictive models did not allow sufficiently accurate identification of the patients at risk during the waiting-time. The consequences of a surgical waiting-time averaging 6 months are serious for AS patients. The death rate is high and a subgroup worsen their prognostic profile, with significantly reduced post-AVR long-term survival as the result.

Aortic Valve↗
PubMed1995

The crystal structure of cyclin A.

BACKGROUND: Eukaryotic cell cycle progression is regulated by cyclin dependent protein kinases (CDKs) whose activity is regulated by association with cyclins and by reversible phosphorylation. Cyclins also determine the subcellular location and substrate specificity of CDKs. Cyclins exhibit diverse sequences but all share homology over a region of approximately 100 amino acids, termed the cyclin box. From the determination of the structure of cyclin A, together with results from biochemical and genetic analyses, we can identify which parts of the cyclin molecular may contribute to cyclin A structure and function. RESULTS: We have solved the crystal structure, at 2.0 A resolution, of an active recombinant fragment of bovine cyclin A, cyclin A-3, corresponding to residues 171-432 of human cyclin A. The cyclin box has an alpha-helical fold comprising five alpha helices. This fold is repeated in the C-terminal region, although this region shares negligible sequence similarity with the cyclin box. CONCLUSIONS: Analysis of residues that are conserved throughout the A, B, and E cyclins identifies two exposed clusters of residues, one of which has recently been shown to be involved in the association with human CDK2. The second cluster may identify another site of cyclin A-protein interaction. Comparison of the structure of the unbound cyclin with the structure of cyclin A complexed with CDK2 reveals that cyclin A does not undergo any significant conformational changes on complex formation. Threading analysis shows that the cyclin-box fold is consistent with the sequences of the transcription factor TFIIB and other functionally related proteins. The structural results indicate a role for the cyclin-box fold both as a template for the cyclin family and as a generalised adaptor molecule in the regulation of transcription.

Algorithms↗
PubMed1995

[Contamination of a water system with sewage].

The purpose of the study was to examine the extent of illness caused by contamination of a waterworks with waste water due to overflow. Structured questionnaires were mailed to all 703 households (the main study group) and four day-care centers supplied by the waterworks as well as a group of 200 randomly chosen households in neighbouring communities with a different water supply. Fourteen hundred and fifty-five persons (88% of respondents in the main study group) reported that they had had symptoms of gastroenteritis, particularly diarrhoea (83%) and vomiting (55%). In the control group, 10% of respondents had had symptoms of gastroenteritis. Onset of diarrhoea correlated well with precipitation (Spearman's correlation coefficient: 0.75; p = 0.0002). No pathogens were found. It is important to be aware of the possibility of water contamination when an increased number of cases of gastroenteritis are observed in a local area and to report even a suspicion of waterborne diseases to the county public health office.

Acute Disease↗
PubMed1995

Structure of influenza virus haemagglutinin complexed with a neutralizing antibody.

Haemagglutinin (HA) is the influenza surface glycoprotein that interacts with infectivity-neutralizing antibodies. As a consequence of this immune pressure, it is the variable virus component, which is important in antigenic drift, that results in recurrent epidemics of influenza. We have determined the crystallographic structure of a complex formed between the antigen-binding fragment (Fab) of a neutralizing antibody and the membrane-distal domain ('HA top') of a HA subunit prepared from HA in its membrane-fusion-active conformation. A dramatic change is seen in the structure of the Fab-combining site on complex formation. Our results indicate that neutralization of infectivity by this antibody involves the inhibition of receptor binding, and demonstrate how influenza virus can maintain its conserved receptor-binding site despite the immune selective pressure for change in this region of the molecule; they also contribute to a complete description of the endosomal pH-induced fusion-active HA structure.

Antibodies, Viral↗
PubMed1995

The structural basis for seryl-adenylate and Ap4A synthesis by seryl-tRNA synthetase.

BACKGROUND: Seryl-tRNA synthetase is a homodimeric class II aminoacyl-tRNA synthetase that specifically charges cognate tRNAs with serine. In the first step of this two-step reaction, Mg.ATP and serine react to form the activated intermediate, seryl-adenylate. The serine is subsequently transferred to the 3'-end of the tRNA. In common with most other aminoacyl-tRNA synthetases, seryl-tRNA synthetase is capable of synthesizing diadenosine tetraphosphate (Ap4A) from the enzyme-bound adenylate intermediate and a second molecule of ATP. Understanding the structural basis for the substrate specificity and the catalytic mechanism of aminoacyl-tRNA synthetases is of considerable general interest because of the fundamental importance of these enzymes to protein biosynthesis in all living cells. RESULTS: Crystal structures of three complexes of seryl-tRNA synthetase from Thermus thermophilus are described. The first complex is of the enzyme with ATP and Mn2+. The ATP is found in an unusual bent conformation, stabilized by interactions with conserved arginines and three manganese ions. The second complex contains seryl-adenylate in the active site, enzymatically produced in the crystal after soaking with ATP, serine and Mn2+. The third complex is between the enzyme, Ap4A and Mn2+. All three structures exhibit a common Mn2+ site in which the cation is coordinated by two active-site residues in addition to the alpha-phosphate group from the bound ligands. CONCLUSIONS: Superposition of these structures allows a common reaction mechanism for seryl-adenylate and Ap4A formation to be proposed. The bent conformation of the ATP and the position of the serine are consistent with nucleophilic attack of the serine carboxyl group on the alpha-phosphate by an in-line displacement mechanism leading to the release of the inorganic pyrophosphate. A second ATP molecule can bind with its gamma-phosphate group in the same position as the beta-phosphate of the original ATP. This can attack the seryl-adenylate with the formation of Ap4A by an identical in-line mechanism in the reverse direction. The divalent cation is essential for both reactions and may be directly involved in stabilizing the transition state.

Adenosine Monophosphate↗
PubMed1995

The crystal structure of p13suc1, a p34cdc2-interacting cell cycle control protein.

p13suc1 binds to p34cdc2 kinase and is essential for cell cycle progression in eukaryotic cells. The crystal structure of S.pombe p13suc1 has been solved to 2.7 A resolution using data collected at the ESRF source, Grenoble, from both native crystals and crystals of a seleno-methionine derivative. The starting point for structure solution was the determination of the six selenium sites by direct methods. The structure is dominated by a four-stranded beta-sheet, with four further alpha-helical regions. p13suc1 crystallizes as a dimer in the asymmetric unit stabilized by the binding of two zinc ions. A third zinc site stabilizes the higher-order crystal packing. The sites are consistent with a requirement for zinc during crystal growth. A likely site for p13suc1-protein interaction is immediately evident on one face of the p13suc1 surface. This region comprises a group of conserved, exposed aromatic and hydrophobic residues below a flexible negatively charged loop. A conserved positively charged area would also present a notable surface feature in the monomer, but is buried at the dimer interface. p13suc1 is larger than its recently solved human homologue p9CKS2, with the extra polypeptide forming a helical N-terminal extension and a surface loop between alpha-helices 3 and 4. Notably, p13suc1 does not show the unusual beta-strand exchange that creates an intimate p9CKS2 dimer. p13suc1 cannot oligomerize to form a stable hexamer as has been proposed for p9CKS2.

Amino Acid Sequence↗
PubMed1994

Analogous inhibitors of elastase do not always bind analogously.

It has been assumed that the structure of a single inhibitor complex is sufficient to define the available subsites of an enzyme that has a unique binding site and a uniquely defined mode for ligand binding--the specificity for these subsites can thus be probed by kinetic experiments. Elastase is an enzyme for which these traditional assumptions, which underlie such structural and kinetic studies, do not hold. Three new crystal structures of elastase complexed to chemically similar inhibitors with similar binding affinities reveal a diversity of binding modes as well as two new subsites on elastase. The existence of multiple binding sites and different binding modes for such similar inhibitors indicates that researchers must proceed with caution when using kinetics to map out protein subsites.

Anilides↗
PubMed1994

Immediate and prolonged effects of pre- versus postoperative epidural analgesia with bupivacaine and morphine on pain at rest and during mobilisation after total knee arthroplasty.

Thirty-two patients scheduled for total knee arthroplasty were randomized to receive an identical epidural blockade initiated 30 min before surgical incision (N = 16), or at closure of the surgical wound (N = 16). Before induction of general anaesthesia the epidural catheter was tested with bupivacaine 7.5 mg.ml-1, 2 ml. General anaesthesia was induced with thiopentone, pancuronium or atracurium, and fentanyl 0.1-0.3 mg, and maintained with N2O/O2 and enflurane. The epidural regimen consisted of a bolus of 16 ml of bupivacaine 7.5 mg.ml-1 plus morphine 2 mg, and continuous infusion of bupivacaine 1.25 mg.ml-1 plus morphine 0.05 mg.ml-1, 4 ml.h-1 for the first 24 h, and bupivacaine 0.625 mg.ml-1 plus morphine 0.05 mg.ml-1, 4 ml.h-1, for the next 24 h after operation. Additional morphine 2.5-5 mg was administered i.v. or i.m. for the first 24 h postoperatively, and ketobemidone or morphine 5-10 mg orally or rectally from 24 h to 7 d postoperatively, on request. Paracetamol 1000 mg every 8 h was administered from 48 h to 7 days postoperatively. No significant differences were observed in request for additional opioids, or in pain scores at rest or during mobilisation of the operated limb, during or after cessation of the epidural regimen. These results do not suggest timing of analgesia with a conventional, continuous epidural regimen to be of major clinical importance in patients undergoing total knee arthroplasty.

Aged↗
PubMed1994

Gastroenteritis: a waterborne outbreak affecting 1600 people in a small Danish town.

STUDY OBJECTIVE: To examine (i) the extent of illness caused by contamination of a waterworks with waste water due to overflow, and its correlation with precipitation; (ii) the potential secondary spread; (iii) economic losses due to sick leave. DESIGN: A historical follow up study with structured postal questionnaires. SETTING: A small community on the outskirts of greater Copenhagen at the end of 1991 and the beginning of 1992. PARTICIPANTS: The main study group comprised all 703 households supplied by the waterworks (response rate: 89% of households). There was a control group of 200 randomly chosen households in neighbouring communities with a different water supply source (response rate: 64% of households). A day care group of all 149 children (response rate: 78%) and 30 teachers (response rate: 83%) who lived in central Copenhagen, but spent the day in four day care centres supplied by the waterworks, and members of their household was also studied. MEASUREMENTS AND MAIN RESULTS: Altogether 1455 people (88% of respondents in the main study group) reported having had symptoms of gastroenteritis, particularly diarrhoea (83%) and vomiting (55%). In the control group, 10% had had symptoms of gastroenteritis. The onset of episodes with diarrhoea correlated well with precipitation (Spearman's correlation coefficient: 0.75; p = 0.0002). The secondary attack rate in household contacts was 12%. No pathogens were found. Affected people stayed home from work for a total of 1658 days. The cost of loss of production because of sick leave amounted to 1,600,000 Danish kroner (180,000 pounds). CONCLUSIONS: The outbreak caused extensive illness correlated with precipitation, showed secondary spread, and was associated with major economic losses. Increased awareness among local physicians and waterworks personnel of the possibility of contamination of the water could have led to earlier intervention and reduced the extent of illness. Outbreaks are often caused by several factors, many of a technical nature, which in this case acted together. It is recommended that attention be paid to each factor.

Adult↗
PubMed1994

Knowledge and use of maternal and child health services by mothers in Papua New Guinea.

A survey was conducted in the coastal area of Morobe Province in Papua New Guinea between March to April 1992 in order to obtain and examine the current health knowledge and practices of mothers with children under two years of age. The purpose of the survey was to gather data for the detailed planning and implementation of a Child Survival Intervention Project funded by USAID. A total of 30 villages in the area were selected utilizing the WHO 30-cluster sampling technique. The results indicated that breastfeeding was a very common practice. However, because nutritional intake was not increased during pregnancy and lactation for many of the women, it is likely that their nutritional intake was insufficient. Although many mothers knew the importance of immunization, they were unclear about the importance of completing immunization series. The utilization of contraceptive methods was very low among women who did not want to have another child within the subsequent two years. The most common methods were injections and pills. The dissemination of health education to isolated rural villages is one of the most important interventions in reducing maternal and infant mortality. As there currently is no health education unit at the Morobe Provincial Department of Health. It is crucial to establish the unit and to emphasize the importance of health education as the tool for disease prevention and health promotion.

Adolescent↗