Real-time tracking of protein unfolding with time-resolved x-ray solution scattering

The correct folding of proteins is of paramount importance for their function, and protein misfolding is believed to be the primary cause of a wide range of diseases. Protein folding has been investigated with time-averaged methods and time-resolved spectroscopy, but observing the structural dynamics of the unfolding process in real-time is challenging. Here, we demonstrate an approach to directly reveal the structural changes in the unfolding reaction. We use nano- to millisecond time-resolved x-ray solution scattering to probe the unfolding of apomyoglobin. The unfolding reaction was triggered using a temperature jump, which was induced by a nanosecond laser pulse. We demonstrate a new strategy to interpret time-resolved x-ray solution scattering data, which evaluates ensembles of structures obtained from molecular dynamics simulations. We find that apomyoglobin passes three states when unfolding, which we characterize as native, molten globule, and unfolded. The molten globule dominates the population under the conditions investigated herein, whereas native and unfolded structures primarily contribute before the laser jump and 30 μs after it, respectively. The molten globule retains much of the native structure but shows a dynamic pattern of inter-residue contacts. Our study demonstrates a new strategy to directly observe structural changes over the cause of the unfolding reaction, providing time- and spatially resolved atomic details of the folding mechanism of globular proteins.

Measurement of Compton scattering from the deuteron and an improved extraction of the neutron electromagnetic polarizabilities

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical Δ(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn=[11.55±1.25(stat)±0.2(BSR)±0.8(th)]×10(-4)  fm(3) and βn=[3.65∓1.25(stat)±0.2(BSR)∓0.8(th)]×10(-4)  fm(3), with χ(2)=45.2 for 44 degrees of freedom.

Photoneutron yields from tungsten in the energy range of the giant dipole resonance

Photoneutron production on the nuclei of high-Z components of medical accelerator heads can lead to a significant secondary dose during a course of bremsstrahlung radiotherapy. However, a quantitative evaluation of secondary neutron dose requires improved data on the photoreaction yields. These have been measured as a function of photon energy, neutron energy and neutron angle for natW, using tagged photons at the MAX-Lab photonuclear facility in Sweden. This work presents neutron yields for natW(gamma, n) and compares these with the predictions of the Monte Carlo code MCNP-GN, developed specifically to simulate photoneutron production at medical accelerators.

Compton scattering from the deuteron and extracted neutron polarizabilities

Differential cross sections for Compton scattering from the deuteron were measured at MAX-Lab for incident photon energies of 55 and 66 MeV at nominal laboratory angles of 45 degrees, 125 degrees, and 135 degrees. Tagged photons were scattered from liquid deuterium and detected in three NaI spectrometers. By comparing the data with theoretical calculations in the framework of a one-boson-exchange potential model, the sum and the difference of the isospin-averaged nucleon polarizabilities, alpha(N)+beta(N)=17.4+/-3.7 and alpha(N)-beta(N)=6.4+/-2.4 (in units of 10(-4) fm(3)), have been determined. By combining the latter with the global-averaged value for alpha(p)-beta(p) and using the predictions of the Baldin sum rule for the sum of the nucleon polarizabilities, we have obtained values for the neutron electric and magnetic polarizabilities of alpha(n)=8.8+/-2.4(total)+/-3.0(model) and beta(n)=6.5-/+2.4(total)-/+3.0(model), respectively.

Prognostic factors for failure of primary patency within a year of bypass to the foot in patients with diabetes and critical ischaemia

OBJECTIVE

To find out whether we could identify prognostic factors for early failure of bypass to the foot in diabetic patients with critical ischaemia.

DESIGN

Retrospective series of consecutive patients.

SETTING

County hospital, Sweden.

PATIENTS

43 diabetic patients who had 48 reconstructions for critical ischaemia between 1988 and 1994.

INTERVENTIONS

48 elective vein bypass procedures to the feet.

MAIN OUTCOME MEASURES

Prognostic factors for primary patency.

RESULTS

Primary and secondary patency rates at one year were 72% (95% confidence interval (CI) 58 to 85) and 83% (95% CI 71 to 95), respectively. Limb salvage and survival rates at one year were 85% (95% CI 74 to 96) and 86% (95% CI 75 to 96), respectively. Vein graft of questionable quality, major wound healing problems, use of the reversed vein technique, and a narrow lumen (< 1.5 mm) of the recipient artery increased the hazard for failed primary patency by 17.3 (p = 0.003), 6.0 (p = 0.02), 4.7 (p = 0.03), and 3.9 (p = 0.05) times, respectively. Short vein bypass (p = 0.70), translocated or composite veins (p = 0.61), major postoperative oedema of the leg (p = 0.46), or questionable quality of the wall of the recipient artery (p = 0.29), however, had no significant independent effect on the primary patency rate.

CONCLUSION

Early primary patency after bypass to the foot in diabetic patients might improve if veins of questionable quality, major wound healing problems, thin reversed veins from the calf, and narrow recipient arteries can be avoided or handled more proficiently than in the present study.

Evaluation of dispatcher-assisted cardiopulmonary resuscitation

The outcome of out-of-hospital cardiac arrest (CA) following cardiopulmonary resuscitation (CPR) initiated by dispatcher-provided telephone instructions (T-CPR) in the area of Gothenburg, Sweden was studied. During a period of 27 months, 475 cases categorized by the dispatchers at the Emergency Co-ordination and Dispatch Centre as being suspected CA were offered T-CPR and were included in one of the following groups: (1) T-CPR completed (caller without previous CPR training); (2) T-CPR completed (caller with previous CPR training); (3) T-CPR started, but not completed; (4) T-CPR declined by caller due to previous CPR training; (5) T-CPR declined by caller due to other reasons; or, (6) T-CPR not offered. Of the patients, 473 could be followed up and of them 427 fulfilled the criteria for CA on ambulance arrival. Among the latter cases, 10% were hospitalized alive, 4% could be discharged from hospital, and the distribution among groups was: (1) 7%; (2) 18%; (3) 5%; (4) 11%; (5) 3%; and (6) 1%. The study concludes that although more attention should be paid to the detection of CA patients by the dispatchers, when the dispatchers suspected CA, their accuracy was high. Half of the witnesses accepted the offer of T-CPR and one-third completed T-CPR. More efforts and research are needed, however, to increase the percentages of callers completing CPR. The impact of T-CPR on survival might be limited. Indeed, the comparison of 'resuscitable' patients in whom T-CPR played an important role in supporting bystanders (i.e. groups 1 and 2) with 'resuscitable' patients in whom T-CPR was not performed (i.e. groups 3, 5 and 6) suggests an increase in survival from 6% (groups 3, 5 and 6) to 9% (groups 1 and 2).

Ambulance despatchers' estimation of intensity of pain and presence of associated symptoms in relation to outcome in patients who call for an ambulance because of acute chest pain

BACKGROUND

A large number of patients who call for an ambulance because of acute chest pain have an acute ischaemic event, but some do not. AIM. To relate the ambulance despatcher's estimated severity of pain and presence of associated symptoms, in patients who call for an ambulance because of acute chest pain, to whether they develop acute myocardial infarction (AMI) and to the risk of early death.

PATIENTS

All those with acute chest pain who contacted the despatch centre in Göteborg over a 2-month period.

RESULTS

In all, 503 patients fulfilled the inclusion criteria. Patients judged as having severe chest pain (68%) developed AMI during the first 3 days in hospital on 26% of occasions as compared with 13% among patients judged as having only vague chest pain (P = 0.0004). The difference was less marked among the elderly and women. The presence of any of the following associated symptoms, dyspnoea, nausea, vertigo, cold sweat or syncope, tended to be associated with a higher infarction rate (24%) than if none of these symptoms was present (17%, P = 0.06). Mortality during the pre-hospital and the hospital phase was not associated with the estimated severity of pain or the presence of associated symptoms.

CONCLUSIONS

The despatcher's estimation of the severity of pain and the presence of associated symptoms appears to be associated with the development of AMI but not with early mortality.

Outcome for patients who call for an ambulance for chest pain in relation to the dispatcher's initial suspicion of acute myocardial infarction

The very early handling of patients with suspected acute myocardial infarction (AMI) is of critical importance to the outcome. The aim of this study was to relate the dispatcher's initial suspicion of AMI, among patients who call for an ambulance due to chest pain, to the subsequent diagnosis and outcome. All patients who called for an ambulance in Gothenburg due to acute chest pain during a 2-month period were included in the study. In all, 503 patients fulfilled the inclusion criteria, and information on the dispatcher's initial suspicion of AMI was available in 484 patients. There was at least a strong suspicion of AMI in 36%, a moderate suspicion of AMI in 34% and only a vague or no suspicion in 30%. Among patients with at least a strong suspicion of AMI, 29% subsequently developed infarcation, compared with 18% among patients with a moderate suspicion of AMI and 15% among patients with only a vague or no suspicion (p < 0.001). However, the priority level was similar in patients with and without a life-threatening condition, and the mortality rate remained similar in patients with a strong suspicion and those without a strong suspicion of AMI. Thus, among patients who called for an ambulance due to acute chest pain there was a direct relationship between the dispatcher's suspicion of AMI and the subsequent diagnosis, but the mortality rate was similar in the different groups.

Vein bypass surgery to the foot in patients with diabetes and critical ischaemia

The feasibility of vein bypass surgery to the arteries of the foot was studied in a diabetic population with critical ischaemia; whether or not such reconstruction leads to an independent lifestyle was assessed 1 year later. Thirty-three reconstructions were performed on 32 limbs in 31 patients. The mortality and reoperation rates within 1 month were both 6 per cent. Primary and secondary patency, limb salvage and survival rates at 1 year were 76, 89, 89 and 82 per cent respectively. Good results in the form of combined survival, patency, limb salvage, walking ability, relief of pain and residence at home were achieved in 64 per cent of patients after 1 year. Reconstructive vascular surgery to the foot in diabetics is feasible and affords two-thirds of patients an independent lifestyle 1 year after surgery.

Mapping and complementation studies of the gene for release factor 1

In Escherichia coli the release factor 1 protein (RF1) recognizes and terminates translation at UAG and UAA codons. Using the technique of ColE1 plasmid integration in polA strains, we have mapped the cloned gene for RF1 to 27 min on the E. coli chromosome. This is the same location as that of the uar gene in which temperature-sensitive mutations increase the suppression of UAG and UAA alleles. In this study we proved that the uar mutation lies in the gene for RF1 by complementation of the uar phenotype with plasmids carrying the RF1 gene and by cloning the uar allele onto the RF1 plasmid by means of homologous recombination. In addition, complementation and P1 mapping data suggest that sueB is also a mutation in the same position as the RF1 gene. We propose that the gene for RF1 be named prfA after protein release factor.