The nucleotide-free state of the multidrug resistance ABC transporter LmrA: Sulfhydryl cross-linking supports a constant contact, head-to-tail configuration of the nucleotide-binding domains

© 2015 Jones, George. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABC transporters are integral membrane pumps that are responsible for the import or export of a diverse range of molecules across cell membranes. ABC transporters have been implicated in many phenomena of medical importance, including cystic fibrosis and multidrug resistance in humans. The molecular architecture of ABC transporters comprises two transmembrane domains and two ATP-binding cassettes, or nucleotide-binding domains (NBDs), which are highly conserved and contain motifs that are crucial to ATP binding and hydrolysis. Despite the improved clarity of recent structural, biophysical, and biochemical data, the seemingly simple process of ATP binding and hydrolysis remains controversial, with a major unresolved issue being whether the NBD protomers separate during the catalytic cycle. Here chemical cross-linking data is presented for the bacterial ABC multidrug resistance (MDR) transporter LmrA. These indicate that in the absence of nucleotide or substrate, the NBDs come into contact to a significant extent, even at 4°C, where ATPase activity is abrogated. The data are clearly not in accord with an inward-closed conformation akin to that observed in a crystal structure of V. cholerae MsbA. Rather, they suggest a head-to-tail configuration 'sandwich' dimer similar to that observed in crystal structures of nucleotide-bound ABC NBDs. We argue the data are more readily reconciled with the notion that the NBDs are in proximity while undergoing intra-domain motions, than with an NBD 'Switch' mechanism in which the NBD monomers separate in between ATP hydrolysis cycles

An Asymmetric Post-Hydrolysis State of the ABC Transporter ATPase Dimer

ABC transporters are a superfamily of enzyme pumps that hydrolyse ATP in exchange for translocation of substrates across cellular membranes. Architecturally, ABC transporters are a dimer of transmembrane domains coupled to a dimer of nucleotide binding domains (NBDs): the NBD dimer contains two ATP-binding sites at the intersubunit interface. A current controversy is whether the protomers of the NBD dimer separate during ATP hydrolysis cycling, or remain in constant contact. In order to investigate the ABC ATPase catalytic mechanism, MD simulations using the recent structure of the ADP+Pi-bound MJ0796 isolated NBD dimer were performed. In three independent simulations of the ADP+Pi/apo state, comprising a total of >0.5 μs, significant opening of the apo (empty) active site was observed; occurring by way of intrasubunit rotations between the core and helical subdomains within both NBD monomers. In contrast, in three equivalent simulations of the ATP/apo state, the NBD dimer remained close to the crystal structure, and no opening of either active site occurred. The results thus showed allosteric coupling between the active sites, mediated by intrasubunit conformational changes. Opening of the apo site is exquisitely tuned to the nature of the ligand, and thus to the stage of the reaction cycle, in the opposite site. In addition to this, in also showing how one active site can open, sufficient to bind nucleotide, while the opposite site remains occluded and bound to the hydrolysis products ADP+Pi, the results are consistent with a Constant Contact Model. Conversely, they show how there may be no requirement for the NBD protomers to separate to complete the catalytic cycle. © 2013 Jones, George

Computational analysis of the MCoTI-II plant defence knottin reveals a novel intermediate conformation that facilitates trypsin binding

MCoTI-I and II are plant defence proteins, potent trypsin inhibitors from the bitter gourd Momordica cochinchinensis. They are members of the Knottin Family, which display exceptional stability due to unique topology comprising three interlocked disulfide bridges. Knottins show promise as scaffolds for new drug development. A crystal structure of trypsin-bound MCoTI-II suggested that loop 1, which engages the trypsin active site, would show decreased dynamics in the bound state, an inference at odds with an NMR analysis of MCoTI-I, which revealed increased dynamics of loop 1 in the presence of trypsin. To investigate this question, we performed unrestrained MD simulations of trypsin-bound and free MCoTI-II. This analysis found that loop 1 of MCoTI-II is not more dynamic in the trypsin-bound state than in the free state. However, it revealed an intermediate conformation, transitional between the free and bound MCoTI-II states. The data suggest that MCoTI-II binding involves a process in which initial interaction with trypsin induces transitions between the free and intermediate conformations, and fluctuations between these states account for the increase in dynamics of loop 1 observed for trypsin-bound MCoTI-I. The MD analysis thus revealed new aspects of the inhibitors dynamics that may be of utility in drug design

Comparing paediatric- and adult-onset linear morphoea in a large tertiary-referral scleroderma centre

Background: Linear morphoea is a severe morphoea subtype associated with extracutaneous manifestations, potentially permanent disfigurement and functional impairment. Linear morphoea is more prevalent in paediatric patients, and knowledge of disease in adults is limited. The objective of this study was to compare paediatric- and adult-onset linear morphoea, in an exclusively adult population. / Methodology: This was a retrospective cohort study of adult patients with linear morphoea seen over a 3-year period at a single-site adult tertiary-referral Connective Tissue Disease centre. Clinical markers of disease severity and course, including anatomical distribution, extracutaneous manifestations, cutaneous symptoms, associated autoimmunity, inflammatory blood parameters, Dermatology Life Quality Index scores, treatment requirements and modified Localised Scleroderma Activity Tool were assessed and compared in paediatric- and adult-onset linear morphoea. / Results: Of 298 patients with morphoea seen during the study period, 135 had linear morphoea and 133 were included in the study. Most were female (78.9%), the mean age was 36.5 years and almost half (43.6%) had adult-onset disease. Disease was similarly severe between groups with regard to anatomical distribution, cutaneous symptoms (n = 89, 66.9%), extracutaneous manifestations (n = 76, 57.1%), antinuclear antibody–positivity (n = 40, 40.4%), raised erythrocyte sedimentation rate (n = 27, 25.0%) and associated autoimmune diagnoses (n = 15, 11.3%). Prescribed treatments were similar between groups; 73.7% receiving methotrexate and almost one-third (32.3%) requiring more than one steroid-sparing agent. Those with paediatric-onset had more disease-related damage, with a mean modified Localised Scleroderma Skin Damage Index score of 19.5 (95% confidence interval: 17.0–22.0) versus 8.1 (95% confidence interval: 4.4–11.8; p < 0.001). Significantly more patients with adult-onset linear morphoea had quiescent disease (p = 0.0332), and even after correcting for disease duration, paediatric-onset patients still had 2.6 times greater odds of active disease (odds ratio = 2.59, 95% confidence interval: 0.9–7.6; p = 0.083). / Conclusion: Linear morphoea in adults can be a severe disease with extracutaneous, autoimmune and systemic features. Adults with paediatric-onset disease appear to have more severe cumulative damage, greater functional impairment and ongoing disease activity. This patient subgroup may require particularly close monitoring and more aggressive therapy

In Silico Investigation of the Binding of MCoTI-II Plant Defense Knottin to the γ-NGF Serine Protease of the 7S Nerve Growth Factor Complex and Biological Activity of Its NGF Mimetic Properties

Copyright © 2019 American Chemical Society. Nerve growth factor (NGF) is an endogenously produced polypeptide that promotes the differentiation, survival, and repair of neurons in the central and peripheral nervous systems. While trophic proteins hold promise for the treatment of neuronal injury and disease, use of NGF is limited by its large molecular weight, lack of permeability through the blood-brain barrier, and peripheral side effects. Previously, we found that an extract of the Momordica cochinchinensis seed stimulated PC-12 neurite outgrowth. Bioactivity-guided fractioning of the seed extract suggested that the NGF mimetic agent was one of few defined proteins from this plant: one group being the defense Knottins and the other group of the lowest mass is the potent trypsin inhibitor MCoTI-II. Here, the NGF mimetic potential of this latter protein was investigated using two concurrent but different approaches. A biological study used recombinant purified MCoTI-II, which when tested in rat PC-12 cells grown on collagen, failed to initiate outgrowth relative to the positive control 7S NGF. In a separate computational study, the possibility was investigated such that MCoTI-II could exert an effect through binding to the serine protease γ-NGF subunit of the 7S NGF complex, analogous to its binding to its native receptor trypsin. Molecular dynamics simulations showed that MCoTI-II can bind stably to γ-NGF for >350 ns. Modeling indicated that this interaction could sterically inhibit 7S NGF complex formation, potentially altering the equilibrium between inactive complexed and free active NFG protein. In conclusion, the biological study now excludes the MCoTI-II protein as the NGF mimetic factor in the Momordica extract, an important and required step to identify the active component in this seed. On the other hand, the theoretical study has revealed a novel observation that may be of use in the development of strategies to affect NGF activity

Examination of the Relationship between In-Store Environmental Factors and Fruit and Vegetable Purchasing among Hispanics.

Retail food environments have received attention for their influence on dietary behaviors and for their nutrition intervention potential. To improve diet-related behaviors, such as fruit and vegetable (FV) purchasing, it is important to examine its relationship with in-store environmental characteristics. This study used baseline data from the "El Valor de Nuestra Salud" study to examine how in-store environmental characteristics, such as product availability, placement and promotion, were associated with FV purchasing among Hispanic customers in San Diego County. Mixed linear regression models indicated that greater availability of fresh FVs was associated with a $0.36 increase in FV purchasing (p = 0.01). Placement variables, specifically each additional square foot of display space dedicated to FVs (p = 0.01) and each additional fresh FV display (p = 0.01), were associated with a$0.02 increase and $0.29 decrease, respectively, in FV purchasing. Introducing FV promotions in the final model was not related to FV purchasing. Exploratory analyses indicated that men reported spending$3.69 fewer dollars on FVs compared to women, controlling for covariates (p = 0.02). These results can help inform interventions targeting in-store environmental characteristics to encourage FV purchasing among Hispanics

A computational investigation of kinetoplastid trans-splicing

Trans-splicing is an unusual process in which two separate RNA strands are spliced together to yield a mature mRNA. We present a novel computational approach which has an overall accuracy of 82% and can predict 92% of known trans-splicing sites. We have applied our method to chromosomes 1 and 3 of Leishmania major, with high-confidence predictions for 85% and 88% of annotated genes respectively. We suggest some extensions of our method to other systems

Diversity antenna for a wrist telephone

A radiotelephone wrist device includes a case having a transceiver and a strap attached to the case for fastening the device to a user's wrist. The strap has a top layer and a bottom layer. The top layer is attached to the bottom layer by a pivot mechanism which facilitates rotating at least a portion of the top layer with respect to the bottom layer. A microphone is located on the strap and electrically connected to the transceiver. A speaker is located at an end of the top layer of the strap and electrically connected to the transceiver. A first antenna is located in the bottom layer of the strap. A second antenna is located in the rotatable portion of the top layer of the strap.Published versio

Purpose in the for-profit firm: a review and framework for management research

Purpose is a concept often used in managerial communities to signal and define a firm’s benevolent and pluralistic approach to its stakeholders beyond its focus on shareholders. While some evidence has linked purpose to positive organizational outcomes such as growth, employee satisfaction, innovation, and superior stock market performance, the definition and application of purpose in management research has been varied and frequently ambiguous. We review literature streams that invoke purpose in the for-profit firm and propose a unifying definition. Next, we develop a framework to study purpose that decouples its framing and formalization within firms from its realization, thus helping to avoid conflation of the presence of purpose with positive organizational outcomes. The framework also highlights internal and external drivers that shape the framing of purpose as well as the influence of the institutional context on its adoption and effectiveness. Finally, we provide a rich agenda for future research on purpose