Structure and dynamics of a compact state of a multidomain protein, the mercuric ion reductase

The functional efficacy of colocalized, linked protein domains is dependent on linker flexibility and system compaction. However, the detailed characterization of these properties in aqueous solution presents an enduring challenge. Here, we employ a novel, to our knowledge, combination of complementary techniques, including small-angle neutron scattering, neutron spin-echo spectroscopy, and all-atom molecular dynamics and coarse-grained simulation, to identify and characterize in detail the structure and dynamics of a compact form of mercuric ion reductase (MerA), an enzyme central to bacterial mercury resistance. MerA possesses metallochaperone-like N-terminal domains (NmerA) tethered to its catalytic core domain by linkers. The NmerA domains are found to interact principally through electrostatic interactions with the core, leashed by the linkers so as to subdiffuse on the surface over an area close to the core C-terminal Hg(II)-binding cysteines. How this compact, dynamical arrangement may facilitate delivery of Hg(II) from NmerA to the core domain is discussed.

X-ray structure of a Hg2+ complex of mercuric reductase (MerA) and quantum mechanical/molecular mechanical study of Hg2+ transfer between the C-terminal and buried catalytic site cysteine pairs

Mercuric reductase, MerA, is a key enzyme in bacterial mercury resistance. This homodimeric enzyme captures and reduces toxic Hg²⁺ to Hg⁰, which is relatively unreactive and can exit the cell passively. Prior to reduction, the Hg²⁺ is transferred from a pair of cysteines (C558′ and C559′ using Tn501 numbering) at the C-terminus of one monomer to another pair of cysteines (C136 and C141) in the catalytic site of the other monomer. Here, we present the X-ray structure of the C-terminal Hg²⁺ complex of the C136A/C141A double mutant of the Tn501 MerA catalytic core and explore the molecular mechanism of this Hg transfer with quantum mechanical/molecular mechanical (QM/MM) calculations. The transfer is found to be nearly thermoneutral and to pass through a stable tricoordinated intermediate that is marginally less stable than the two end states. For the overall process, Hg²⁺ is always paired with at least two thiolates and thus is present at both the C-terminal and catalytic binding sites as a neutral complex. Prior to Hg²⁺ transfer, C141 is negatively charged. As Hg²⁺ is transferred into the catalytic site, a proton is transferred from C136 to C559′ while C558′ becomes negatively charged, resulting in the net transfer of a negative charge over a distance of ∼7.5 Å. Thus, the transport of this soft divalent cation is made energetically feasible by pairing a competition between multiple Cys thiols and/or thiolates for Hg²⁺ with a competition between the Hg²⁺ and protons for the thiolates.

Evaluation of microsatellite markers for populations studies and forensic identification of African lions (Panthera leo)

The South African lion (Panthera leo) population is highly fragmented. One-third of its wild lions occur in small (<1000 km(2)) reserves. These lions were reintroduced from other areas of the species' historical range. Management practices on these reserves have not prioritized genetic provenance or heterozygosity. These trends potentially constrain the conservation value of these lions. To ensure the best management and long-term survival of these subpopulations as a viable collective population, the provenance and current genetic diversity must be described. Concurrently, poaching of lions to supply a growing market for lion bones in Asia may become a serious conservation challenge in the future. Having a standardized, validated method for matching confiscated lion parts with carcasses will be a key tool in investigating these crimes. We evaluated 28 microsatellites in the African lion using samples from 18 small reserves and 1 captive facility in South Africa, two conservancies in Zimbabwe, and Kruger National and Kgalagadi Transfrontier Parks to determine the loci most suited for population management and forensic genetic applications. Twelve microsatellite loci with a match probability of 1.1×10(-5) between siblings were identified for forensics. A further 10 could be added for population genetics studies.

Attitudinal barriers to participation in oncology clinical trials: factor analysis and correlates of barriers

Patient participation in cancer clinical trials is low. Little is known about attitudinal barriers to participation, particularly among patients who may be offered a trial during an imminent initial oncology consult. The aims of the present study were to confirm the presence of proposed subscales of a recently developed cancer clinical trial attitudinal barriers measure, describe the most common cancer clinical trials attitudinal barriers, and evaluate socio-demographic, medical and financial factors associated with attitudinal barriers. A total of 1256 patients completed a survey assessing demographic factors, perceived financial burden, prior trial participation and attitudinal barriers to clinical trials participation. Results of a factor analysis did not confirm the presence of the proposed four attitudinal barriers subscale/factors. Rather, a single factor represented the best fit to the data. The most highly-rated barriers were fear of side-effects, worry about health insurance and efficacy concerns. Results suggested that less educated patients, patients with non-metastatic disease, patients with no previous oncology clinical trial participation, and patients reporting greater perceived financial burden from cancer care were associated with higher barriers. These patients may need extra attention in terms of decisional support. Overall, patients with fewer personal resources (education, financial issues) report more attitudinal barriers and should be targeted for additional decisional support.

Effects of troponin T cardiomyopathy mutations on the calcium sensitivity of the regulated thin filament and the actomyosin cross-bridge kinetics of human β-cardiac myosin

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) lead to significant cardiovascular morbidity and mortality worldwide. Mutations in the genes encoding the sarcomere, the force-generating unit in the cardiomyocyte, cause familial forms of both HCM and DCM. This study examines two HCM-causing (I79N, E163K) and two DCM-causing (R141W, R173W) mutations in the troponin T subunit of the troponin complex using human β-cardiac myosin. Unlike earlier reports using various myosin constructs, we found that none of these mutations affect the maximal sliding velocities or maximal Ca²⁺-activated ADP release rates involving the thin filament human β-cardiac myosin complex. Changes in Ca²⁺ sensitivity using the human myosin isoform do, however, mimic changes seen previously with non-human myosin isoforms. Transient kinetic measurements show that these mutations alter the kinetics of Ca²⁺ induced conformational changes in the regulatory thin filament proteins. These changes in calcium sensitivity are independent of active, cycling human β-cardiac myosin.

Abstract P6-09-05: Women's perceptions of lymphedema risk management: Psychological factors do matter

Introduction: Lymphedema arising from breast cancer surgery and treatment is characterized by arm impairment, physical disfigurement, emotional distress and diminished quality of life. Given no specific lymphedema cure, early detection and risk management strategies are recommended. The American Cancer Society (ACS) identifies simple behavioral strategies to minimize lymphedema risk; however, little is known about women's adherence to these recommendations over time. Even less is known about how women perceive lymphedema risk and the psychological factors that promote long-term adherence. Guided by the Cognitive-Social Health Information Processing model we assessed adherence to risk management strategies and identified psychological factors associated with adherence.

Methods: Women (N = 103) diagnosed with primary breast cancer and scheduled for breast surgery initially completed the baseline questionnaire prior to surgery, and then received the ACS publication “Lymphedema: What Every Woman With Breast Cancer Should Know” as part of usual care. Follow-up questionnaires were completed by participants 6- and 12-months later. Baseline data collected included demographic and medical history variables, lymphedema-related knowledge and cognitive and affective factors (perceived risk, beliefs and expectancies, self-regulatory competencies, negative affect), and adherence to risk management strategies. Adherence was also assessed at 6- and 12-months. A mixed-model maximum-likelihood logistic regression was employed in data analyses.

Results: Adherence to risk minimization strategies increased over time (p &lt; .001) and varied with the specific strategy (p &lt; .001). Risk minimization strategies fell into three broad groupings: 1) High levels of consistent adherence across time - wearing loose clothing, avoiding tight jewelry, avoiding blood pressure readings and avoiding trauma to the arm; 2) Moderate levels of adherence and greater variability across time - avoiding cutting cuticles, extreme sun exposure, carrying heavy bags, and temperature extremes, and consulting with a doctor when symptoms appear; 3) Low level of adherence - wearing protective gloves and using an electric razor. Baseline knowledge was associated with adherence to all strategies. In addition, increased self-efficacy to enact the strategies (OR = 1.82, p = 0.0001), greater beliefs in one's self-regulatory ability to manage distress (OR = 1.25, p = 0.0017), and decreased risk-related negative affect (OR = 0.96, p = 0.03) were associated with increased adherence to the recommendations.

Conclusions: During the 12 months following breast cancer diagnosis, women demonstrated increased awareness of lymphedema risk management and adherence to the recommended strategies, although adherence to individual strategies varied. Psychological factors were associated with adherence to recommendations. Specifically, women with greater knowledge, self-efficacy to enact recommended strategies and ability to self-regulate negative emotions, and lower negative affect were more likely to be adherent. These findings suggest that for lymphedema education approaches to be maximally effective, they should incorporate psychological interventions designed to enhance self-efficacy and coping in women at risk to ensure long-term adherence.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-09-05.

The relationships among knowledge, self-efficacy, preparedness, decisional conflict, and decisions to participate in a cancer clinical trial

BACKGROUND

Cancer clinical trials (CCTs) are important tools in the development of improved cancer therapies; yet, participation is low. Key psychosocial barriers exist that appear to impact a patient's decision to participate. Little is known about the relationship among knowledge, self-efficacy, preparation, decisional conflict, and patient decisions to take part in CCTs.

OBJECTIVE

The purpose of this study was to determine if preparation for consideration of a CCT as a treatment option mediates the relationship between knowledge, self-efficacy, and decisional conflict. We also explored whether lower levels of decisional conflict are associated with greater likelihood of CCT enrollment.

METHOD

In a pre-post test intervention study, cancer patients (N = 105) were recruited before their initial consultation with a medical oncologist. A brief educational intervention was provided for all patients. Patient self-report survey responses assessed knowledge, self-efficacy, preparation for clinical trial participation, decisional conflict, and clinical trial participation.

RESULTS

Preparation was found to mediate the relationship between self-efficacy and decisional conflict (p = 0.003 for a test of the indirect mediational pathway for the decisional conflict total score). Preparation had a more limited role in mediating the effect of knowledge on decisional conflict. Further, preliminary evidence indicated that reduced decisional conflict was associated with increased clinical trial enrollment (p = 0.049).

CONCLUSIONS

When patients feel greater CCT self-efficacy and have more knowledge, they feel more prepared to make a CCT decision. Reduced decisional conflict, in turn, is associated with the decision to enroll in a clinical trial. Our results suggest that preparation for decision-making should be a target of future interventions to improve participation in CCTs.

Discovering mercury protein modifications in whole proteomes using natural isotope distributions observed in liquid chromatography-tandem mass spectrometry

The identification of peptides that result from post-translational modifications is critical for understanding normal pathways of cellular regulation as well as identifying damage from, or exposures to xenobiotics, i.e. the exposome. However, because of their low abundance in proteomes, effective detection of modified peptides by mass spectrometry (MS) typically requires enrichment to eliminate false identifications. We present a new method for confidently identifying peptides with mercury (Hg)-containing adducts that is based on the influence of mercury's seven stable isotopes on peptide isotope distributions detected by high-resolution MS. Using a pure protein and E. coli cultures exposed to phenyl mercuric acetate, we show the pattern of peak heights in isotope distributions from primary MS single scans efficiently identified Hg adducts in data from chromatographic separation coupled with tandem mass spectrometry with sensitivity and specificity greater than 90%. Isotope distributions are independent of peptide identifications based on peptide fragmentation (e.g. by SEQUEST), so both methods can be combined to eliminate false positives. Summing peptide isotope distributions across multiple scans improved specificity to 99.4% and sensitivity above 95%, affording identification of an unexpected Hg modification. We also illustrate the theoretical applicability of the method for detection of several less common elements including the essential element, selenium, as selenocysteine in peptides.

High-flow nasal cannula and extubation success in the premature infant: a comparison of two modalities

OBJECTIVE

To compare the effectiveness of Fisher and Paykel (FP) and Vapotherm (VT) high-flow nasal cannula (HFNC) in preventing reintubation either within 72 h or <7 days after extubation of premature infants. The primary outcome was the rate of extubation failure defined as reintubation within 72 h. Secondary outcomes included reintubation after ≤7 days.

STUDY DESIGN

This was a prospective, randomized pilot study comparing the extubation success of 40 infants born between 26 and 29 weeks of gestation.

RESULT

The rate of extubation failure at 72 h was 18% for FP and 9% for VT. The failure rate ≤7 days after extubation was 30% for FP and 27% for VT. None of these differences were statistically significant.

CONCLUSION

There was no difference between FP and VT in the extubation success of infants born between 26 and 29 weeks.

Direct measurement of mercury(II) removal from organomercurial lyase (MerB) by tryptophan fluorescence: NmerA domain of coevolved γ-proteobacterial mercuric ion reductase (MerA) is more efficient than MerA catalytic core or glutathione

Aerobic and facultative bacteria and archaea harboring mer loci exhibit resistance to the toxic effects of Hg(II) and organomercurials [RHg(I)]. In broad spectrum resistance, RHg(I) is converted to less toxic Hg(0) in the cytosol by the sequential action of organomercurial lyase (MerB: RHg(I) → RH + Hg(II)) and mercuric ion reductase (MerA: Hg(II) → Hg(0)) enzymes, requiring transfer of Hg(II) from MerB to MerA. Although previous studies with γ-proteobacterial versions of MerA and a nonphysiological Hg(II)-DTT-MerB complex qualitatively support a pathway for direct transfer between proteins, assessment of the relative efficiencies of Hg(II) transfer to the two different dicysteine motifs in γ-proteobacterial MerA and to competing cellular thiol is lacking. Here we show the intrinsic tryptophan fluorescence of γ-proteobacterial MerB is sensitive to Hg(II) binding and use this to probe the kinetics of Hg(II) removal from MerB by the N-terminal domain (NmerA) and catalytic core C-terminal cysteine pairs of its coevolved MerA and by glutathione (GSH), the major competing cellular thiol in γ-proteobacteria. At physiologically relevant concentrations, reaction with a 10-fold excess of NmerA over HgMerB removes ≥92% Hg(II), while similar extents of reaction require more than 1000-fold excess of GSH. Kinetically, the apparent second-order rate constant for Hg(II) transfer from MerB to NmerA, at (2.3 ± 0.1) × 10(4) M(-1) s(-1), is ∼100-fold greater than that for GSH ((1.2 ± 0.2) × 10(2) M(-1) s(-1)) or the MerA catalytic core (1.2 × 10(2) M(-1) s(-1)), establishing transfer to the metallochaperone-like NmerA domain as the kinetically favored pathway in this coevolved system.

Chromosomes from testicular preparations of lepidoptera

Typical elongate, beaded chromosomes have been observed in squash preparations of testicular tissue of the butterfly Speyeria aphrodite (Fabricius), the first demonstration of relatively uncondensed chromosomes in the Lepidoptera.

Structure and conformational dynamics of the metalloregulator MerR upon binding of Hg(II)

The bacterial metalloregulator MerR is the index case of an eponymous family of regulatory proteins, which controls the transcription of a set of genes (the mer operon) conferring mercury resistance in many bacteria. Homodimeric MerR represses transcription in the absence of mercury and activates transcription upon Hg(II) binding. Here, the average structures of the apo and Hg(II)-bound forms of MerR in aqueous solution are examined using small-angle X-ray scattering, indicating an extended conformation of the metal-bound protein and revealing the existence of a novel compact conformation in the absence of Hg(II). Molecular dynamics (MD) simulations are performed to characterize the conformational dynamics of the Hg(II)-bound form. In both small-angle X-ray scattering and MD, the average torsional angle between DNA-binding domains is approximately 65 degrees. Furthermore, in MD, interdomain motions on a timescale of approximately 10 ns involving large-amplitude (approximately 20 A) domain opening-and-closing, coupled to approximately 40 degrees variations of interdomain torsional angle, are revealed. This correlated domain motion may propagate allosteric changes from the metal-binding site to the DNA-binding site while maintaining DNA contacts required to initiate DNA underwinding.

Literacy assessment of family health history tools for public health prevention

OBJECTIVES

This study aimed to systematically identify and evaluate the readability and document complexity of currently available family history tools for the general public.

METHODS

Three steps were undertaken to identify family history tools for evaluation: (a) Internet searches, (b) expert consultation, and (c) literature searches. Tools identified were assessed for readability using the Simple Measure of Gobbledygook (SMOG) readability formula. The complexity of documents (i.e., forms collecting family history information) was assessed using the PMOSE/IKIRSCH document readability formula.

RESULTS

A total of 78 tools were identified, 47 of which met the criteria for inclusion. SMOG reading grade levels for multimedia-based tools ranged from 10.1 to 18.3, with an average score of 13.6. For print-based tools, SMOG ranged from 8.7 to 14.1, with an average score of 12.0. Document complexity ranged from very low complexity (level 1 proficiency) to high complexity (level 4 proficiency).

CONCLUSION

The majority of tools are written at a reading grade level that is beyond the 8th grade average reading level in the United States. The lack of family history tools that are easy to read or use may compromise their potential effectiveness in identifying individuals at increased risk for chronic diseases in the general population.