Dramatic acceleration of protein folding by stabilization of a nonnative backbone conformation

Through a mutagenic investigation of Gly-48, a highly conserved position in the Src homology 3 domain, we have discovered a series of amino acid substitutions that are highly destabilizing, yet dramatically accelerate protein folding, some up to 10-fold compared with the wild-type rate. The unique folding properties of these mutants allowed for accurate measurement of their folding and unfolding rates in water with no denaturant by using an NMR spin relaxation dispersion technique. A strong correlation was found between beta-sheet propensity and the folding rates of the Gly-48 mutants, even though Gly-48 lies in an unusual non-beta-strand backbone conformation in the native state. This finding indicates that the accelerated folding rates of the Gly-48 mutants are the result of stabilization of a nonnative beta-strand conformation in the transition-state structure at this position, thus providing the first, to our knowledge, experimentally elucidated example of a mechanism by which folding can occur fastest through a nonnative conformation. We also demonstrate that residues that are most stabilizing in the transition-state structure are most destabilizing in the native state, and also cause the greatest reductions in in vitro functional activity. These data indicate that the unusual native conformation of the Gly-48 position is important for function, and that evolutionary selection for function can result in a domain that folds at a rate far below the maximum possible.     

Magnetic tests for magnetosome chains in Martian meteorite ALH84001

Transmission electron microscopy studies have been used to argue that magnetite crystals in carbonate from Martian meteorite ALH84001 have a composition and morphology indistinguishable from that of magnetotactic bacteria. It has even been claimed from scanning electron microscopy imaging that some ALH84001 magnetite crystals are aligned in chains. Alignment of magnetosomes in chains is perhaps the most distinctive of the six crystallographic properties thought to be collectively unique to magnetofossils. Here we use three rock magnetic techniques, low-temperature cycling, the Moskowitz test, and ferromagnetic resonance, to sense the bulk composition and crystallography of millions of ALH84001 magnetite crystals. The magnetic data demonstrate that although the magnetite is unusually pure and fine-grained in a manner similar to terrestrial magnetofossils, most or all of the crystals are not arranged in chains.     

p19Arf induces p53-dependent apoptosis during Abelson virus-mediated pre-B cell transformation

The Ink4a/Arf locus encodes p16^Ink4a and p19^Arf and is among the most frequently mutated tumor suppressor loci in human cancer. In mice, many of these effects appear to be mediated by interactions between p19^Arf and the p53 tumor-suppressor protein. Because Tp53 mutations are a common feature of the multistep pre-B cell transformation process mediated by Abelson murine leukemia virus (Ab-MLV), we examined the possibility that proteins encoded by the Ink4a/Arf locus also play a role in Abelson virus transformation. Analyses of primary transformants revealed that both p16^Ink4a and p19^Arf are expressed in many of the cells as they emerge from the apoptotic crisis that characterizes the transformation process. Analyses of primary transformants from Ink4a/Arf null mice revealed that these cells bypassed crisis. Because expression of p19^Arf but not p16 ^Ink4a induced apoptosis in Ab-MLV-transformed pre-B cells, p19^Arf appears to be responsible for these events. Consistent with the link between p19^Arf and p53, Ink4a/Arf expression correlates with or precedes the emergence of cells expressing mutant p53. These data demonstrate that p19^Arf is an important part of the cellular defense mounted against transforming signals from the Abl oncoprotein and provide direct evidence that the p19^Arf–p53 regulatory loop plays an important role in lymphoma induction.     

Prevention of Contrast and Radiation Injury During Coronary Angiography and Percutaneous Coronary Intervention

Purpose of review

In this review, we provide a summary of the recently published literature on various methods of preventing contrast-induced acute kidney injury (CI-AKI) and radiation-related injuries associated with cardiac catheterization and percutaneous coronary intervention (PCI).

Recent findings

The overall reported incidence of CI-AKI is declining, primarily due to adaptation of a standardized definition for CI-AKI as well as implementation of pre-procedural protocols to prevent or decrease the risk of CI-AKI. The implementation of increasing awareness and establishing radiation protection culture has been shown to be effective measures in reducing radiation exposure.

Summary

Coronary angiography and PCI are valuable diagnostic and therapeutic tools in cardiovascular medicine. Accurate imaging of the coronary arteries in cardiac catheterization is dependent on the use of intravascular injection of iodinated contrast media and fluoroscopic imaging. Patients undergoing diagnostic and interventional cardiac catheterization may be exposed to a substantial amount of contrast media and ionizing radiation. Administration of contrast media is correlated with increased risk of CI-AKI, and exposure to radiation is known to be associated with a spectrum of acute and chronic tissue injuries.

     

Optimal target temperature for slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia

Objective To define optimal target temperature for the slow pathway ablation.Materials and methods In this study, 268 patients with atrioventricular nodal reentrant tachycardia (190 females; mean age, 49 ± 14 years) who underwent slow pathway ablation using a combined electroanatomic approach were enrolled. The patients were categorized into Group 1 if target temperature was <55°C or into Group 2 if target temperature was ≥55°C. Group 2 was divided into three subgroups of 55°C (Sgp-1), 60°C (Sgp-2), and 65°C (Sgp-3).Results Acute success rate was similar in both groups (P = 0.83). The ablation time (26.2 ± 20 vs. 36.5 ± 28 min; P = 0.014), fluoroscopy time (11.6 ± 9.7 vs. 17.8 ± 16.6 min; P = 0.035), and number of applications (4.1 ± 3.2 vs. 9.1 ± 6.5; P = 0.02) were lower for Group 2 than Group 1 patients. The frequency of AV or VA block, impedance rise, and coagulum formation were comparable in two groups (all P > 0.05). During mean follow-up of 14 ± 3 months, recurrence of the arrhythmia was seen in higher proportion of Group 1 than Group 2 patients (P = 0.036). Among the Group 2 patients, there were no significant differences between the three subgroups in terms of acute success rate, fluoroscopy time, risks of AV and VA block, pericardial effusion, and recurrence (All P > 0.05). Number of applications and RF pulse duration were lower in Sgp-2 and 3 compared to Sgp-1 (All P > 0.05). Impedance rise and coagulum formation were slightly higher in Sgp-3 compared to Sgp-1 and 2 but this difference did not reach statistical significance (All P > 0.05).Conclusions Compared to less than 55°C, target temperatures ≥55°C during slow pathway ablation significantly reduces fluoroscopy time, RF pulse duration, number of RF applications, and recurrence of AVNRT without increase in risk of AV or VA block or coagulum formation.     

Rituximab (anti-CD20 monoclonal antibody) as single first-line therapy for patients with follicular lymphoma with a low tumor burden: clinical and molecular evaluation

The clinical activity of rituximab, a chimeric monoclonal antibodywhich binds to the CD20 antigen, was evaluated as a single first-linetherapy for patients with follicular non-Hodgkin lymphoma (NHL). Fiftypatients with follicular CD20⁺ NHL and a low tumor burdenwere analyzed for clinical and molecular responses. They received 4 weekly infusions of rituximab at a dose of 375 mg/m². Theresponse rate a month after treatment (day 50) was 36 of 49 (73%),with 10 patients in complete remission, 3 patients in completeremission/unconfirmed, and 23 patients in partial remission. Tenpatients had stable disease, and the disease progressed in 3 patients. One of 13 (8%) patients in complete remission, 9 of 23 (39%) patients in partial remission, and 5 of 10 (50%) patients withstable disease exhibited disease progression during the first year.Within the study population, 32 patients were initially informative forpolymerase chain reaction (PCR) data on bcl-2-J_H rearrangement. On day 50, 17 of 30 patients (57%) were negative forbcl-2-J_H rearrangement in peripheral blood, and 9 of 29 (31%) were negative in bone marrow; a significant association wasobserved between molecular and clinical responses(P < .0001). At month 12, 16 of 26 patients (62%) werePCR negative in peripheral blood. These results indicate that earlymolecular responses can be sustained for up to 12 months and that thisresponse is highly correlated with progression-free survival. Rituximabhas a high clinical activity and a low toxicity and induces a highcomplete molecular response rate in patients with follicular lymphomaand a low tumor burden.     

Discrete Choice Experiment to Estimate Breast Cancer Patients’ Preferences and Willingness to Pay for Prophylactic Granulocyte Colony-Stimulating Factors

ObjectivesRising out-of-pocket costs for cancer patients have increased shared decision making. Clinical guidelines recommend prophylactic granulocyte colony-stimulating factor (G-CSF) for patients receiving chemotherapy with a 20% or greater risk of febrile neutropenia. A discrete choice experiment was conducted to explore breast cancer patients’ preferences and willingness to pay (WTP) for prophylactic G-CSF to decrease the risk of chemotherapy-induced febrile neutropenia.MethodsAn online discrete choice experiment questionnaire survey of a national US convenience sample of self-reported breast cancer patients with prior chemotherapy treatment was conducted. Sixteen paired G-CSF treatment scenarios, each with four attributes (risk of disruption to chemotherapy schedule due to low white blood cell counts, risk of developing an infection requiring hospitalization, frequency of administration, and total out-of-pocket cost) were presented with a follow-up “no treatment” option. Participant preferences and WTP out of pocket were estimated by logistic regression.ResultsParticipants (n = 296) preferred G-CSF regimens with lower out-of-pocket costs, lower risk of chemotherapy disruption, lower risk of infection, and greater convenience (one G-CSF injection per chemotherapy cycle). Participants’ WTP was $1076 out of pocket per cycle to reduce the risk (high to low) of disrupting their chemotherapy schedule, $884 per cycle to reduce the risk (24% [high] to 7% [low]) of infection, and $851 per cycle to decrease the number of G-CSF injections (11 to 1) per cycle.ConclusionsParticipants highly valued specific features of prophylactic G-CSF treatment including maintaining their chemotherapy schedule, lowering their risk of infection, and reducing the number of injections. Physicians should consider patient preferences to inform the best treatment choices for individual patients.     

One year after twin earthquakes in Northwest Iran

Every year in most earthquakes more than thousands of lives are lost, mainly in middle- and low-income countries. Disability and rehabilitation in third world countries could cause disastrous negative effect in living expense of families. So many preventable disabilities are result of these earthquakes and we hope reminding it will make a difference.     

Septic Coronary Artery Embolism Treated with Aspiration Thrombectomy: Case Report and Review of Literature

Coronary embolization is a potentially fatal sequela of endocarditis. We report a case of Candida endocarditis with septic embolism to the left anterior descending coronary artery. This embolism was successfully treated with aspiration thrombectomy followed by balloon angioplasty. The treatment of acute coronary syndrome in the presence of septic embolism is controversial. Aspiration thrombectomy has been performed in this situation before, and it appears to be safer and more feasible than is thrombolysis or percutaneous transluminal angioplasty.