The High-Resolution Structures of the Neutral and the Low pH Crystals of Aminopeptidase from \u3cem\u3eAeromonas proteolytica\u3c/em\u3e

The aminopeptidase from Aeromonas proteolytica (AAP) contains two zinc ions in the active site and catalyzes the degradation of peptides. Herein we report the crystal structures of AAP at 0.95-Å resolution at neutral pH and at 1.24-Å resolution at low pH. The combination of these structures allowed the precise modeling of atomic positions, the identification of the metal bridging oxygen species, and insight into the physical properties of the metal ions. On the basis of these structures, a new putative catalytic mechanism is proposed for AAP that is likely relevant to all binuclear metalloproteases

Giant Magnetic Moments of Nitrogen Stabilized Mn Clusters and Their Relevance to Ferromagnetism in Mn Doped GaN

Using first principles calculations based on density functional theory, we show that the stability and magnetic properties of small Mn clusters can be fundamentally altered by the presence of nitrogen. Not only are their binding energies substantially enhanced, but also the coupling between the magnetic moments at Mn sites remains ferromagnetic irrespective of their size or shape. In addition, these nitrogen stabilized Mn clusters carry giant magnetic moments ranging from 4 Bohr magnetons in MnN to 22 Bohr magnetons in Mn_5N. It is suggested that the giant magnetic moments of Mn_xN clusters may play a key role in the ferromagnetism of Mn doped GaN which exhibit a wide range (10K - 940K) of Curie temperatures

Scholar-activists in an expanding European food sovereignty movement

This article analyzes the roles, relations, and positions of scholar-activists in the European food sovereignty movement. In doing so, we document, make visible and question the political dimensions of researchers' participation in the movement. We argue that scholar-activists are part of the movement, but are distinct from the affected constituencies, put in place to ensure adequate representation of key movement actors. This is because scholar-activists lack a collective identity, have no processes to formulate collective demands, and no mechanisms for inter-researcher and researchers-movement communication. We reflect on whether and how scholar-activists could organize, and discuss possible pathways for a more cohesive and stronger researcher engagement in the movement.</p

Apoptosis and failure of checkpoint kinase 1 activation in human induced pluripotent stem cells under replication stress

Background: Human induced pluripotent stem (hiPS) cells have the ability to undergo self-renewal and differentiation similarly to human embryonic stem (hES) cells. We have recently shown that hES cells under replication stress fail to activate checkpoint kinase 1 (CHK1). They instead commit to apoptosis, which appears to be a primary defense mechanism against genomic instability. It is not known whether the failure of CHK1 activation and activation of apoptosis under replication stress is solely a feature of hES cells, or if it is a feature that can be extended to hiPS cells. Methods: Here we generated integration-free hiPS cell lines by mRNA transfection, and characterised the cell lines. To investigate the mechanism of S phase checkpoint activation, we have induced replication stress by adding excess thymidine to the cell culture medium, and performed DNA content analysis, apoptosis assays and immunoblottings. Results: We are showing that hiPS cells similarly to hES cells, fail to activate CHK1 when exposed to DNA replication inhibitors and commit to apoptosis instead. Our findings also suggest the Ataxia Telangiectasia Mutated pathway might be responding to DNA replication stress, resulting in apoptosis. Conclusion: Together, these data suggest that the apoptotic response was properly restored during reprogramming with mRNA, and that apoptosis is an important mechanism shared by hiPS and hES cells to maintain their genomic integrity when a replication stress occurs

Investigating the structure and meaning of public service motivation across populations: Developing an international instrument and addressing issues of measurement invariance

The growth in international research on public service motivation (PSM) raises a number of important questions about the degree to which the theory and research developed in one country can contribute to our understanding of PSM in other counties. To help address this issue, this study revisits the conceptual and operational definitions of PSM to address weaknesses previously noted in the literature. Although some important steps have been taken to both improve and internationalize the PSM scale, this work has been done incrementally. In contrast, this study takes a more systematic and comprehensive approach by combining the efforts of international PSM scholars to develop and then test a revised measurement instrument for PSM in 12 countries. Although the resulting four dimensional 16-item measure of PSM reported here provides a better theoretical and empirical foundation for the measurement of PSM, our results suggest that the exact meaning and scaling of PSM dimensions are likely to differ across cultures and languages. These results raise serious concerns regarding the ability to develop a single universal scale of PSM, or making direct comparisons of PSM across countries. © 2012 The Author

Dynamic assessment of word learning skills of preschool children with primary language impairment

Dynamic assessment has been shown to have considerable theoretical and clinical significance in the assessment of socially disadvantaged and culturally and linguistically diverse children. In this study it is used to enhance assessment of pre-school children with primary language impairment. The purpose of the study was to determine whether a dynamic assessment (DA) has the potential to enhance the predictive capacity of a static measure of receptive vocabulary in pre-school children. Forty pre-school children were assessed using the static British Picture Vocabulary Scale (BPVS), a DA of word learning potential and an assessment of non-verbal cognitive ability. Thirty-seven children were followed up 6 months later and re-assessed using the BPVS. Although the predictive capacity of the static measure was found to be substantial, the DA increased this significantly especially for children with static scores below the 25th centile. The DA of children's word learning has the potential to add value to the static assessment of the child with low language skills, to predict subsequent receptive vocabulary skills and to increase the chance of correctly identifying children in need of ongoing support

Reform, Justice, and Sovereignty: A Food Systems Agenda for Environmental Communication

Food ecologies and economies are vital to the survival of communities, non-human species, and our planet. While environmental communication scholars have legitimated food as a topic of inquiry, the entangled ecological, cultural, economic, racial, colonial, and alimentary relations that sustain food systems demand greater attention. In this essay, we review literature within and beyond environmental communication, charting the landscape of critical food work in our field. We then illustrate how environmental justice commitments can invigorate interdisciplinary food systems-focused communication scholarship articulating issues of, and critical responses to, injustice and inequity across the food chain. We stake an agenda for food systems communication by mapping three orientations—food system reform, justice, and sovereignty—that can assist in our critical engagements with and interventions into the food system. Ultimately, we entreat environmental communication scholars to attend to the bends, textures, and confluences of these orientations so that we may deepen our future food-related inquiries

Martian Chlorobenzene Identified by Curiosity in Yellowknife Bay: Evidence for the Preservation of Organics in a Mudstone on Mars

The Sample Analysis at Mars (SAM) instrument on the Curiosity rover is designed to determine the inventory of organic and inorganic volatiles thermally evolved from solid samples using a combination of evolved gas analysis (EGA), gas chromatography mass spectrometry (GCMS), and tunable laser spectroscopy. The first sample analyzed by SAM at the Rocknest (RN) aeolian deposit revealed chlorohydrocarbons derived primarily from reactions between a martian oxychlorine phase (e.g. perchlorate) and terrestrial carbon from N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) vapor present in the SAM instrument background. No conclusive evidence for martian chlorohydrocarbons in the RN sand was found. After RN, Curiosity traveled to Yellowknife Bay and drilled two holes separated by 2.75 m designated John Klein (JK) and Cumberland (CB). Analyses of JK and CB by both SAM and the CheMin x-ray diffraction instrument revealed a mudstone (called Sheepbed) consisting of approx.20 wt% smectite clays, which on Earth are known to aid the concentration and preservation of organic matter. Last year at LPSC we reported elevated abundances of chlorobenzene (CBZ) and a more diverse suite of chlorinated hydrocarbons including dichloroalkanes in CB compared to RN, suggesting that martian or meteoritic organic compounds may be preserved in the mudstone. Here we present SAM data from additional analyses of the CB sample and of Confidence Hills (CH), another drill sample collected at the base of Mt. Sharp. This new SAM data along with supporting laboratory analog experiments indicate that most of the chlorobenzene detected in CB is derived from martian organic matter preserved in the mudstone