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Orange, CA, United States

Chapman University is a private, non-profit university located in Orange, California, affiliated with the Christian Church . Chapman University encompasses seven schools and colleges: Lawrence and Kristina Dodge College of Film and Media Arts, Wilkinson College of Humanities and Social science, George L. Argyros School of Business and Economics, Schmid College of Science & Technology, College of Performing Arts, Dale E. Fowler School of Law and College of Educational Studies. For the 2010–11 academic year, Chapman University enrolled 6,398 students. Wikipedia.

Allosteric interactions of the molecular chaperone Hsp90 with a large cohort of cochaperones and client proteins allow for molecular communication and event coupling in signal transduction networks. The integration of cochaperones into the Hsp90 system is driven by the regulatory mechanisms that modulate the progression of the ATPase cycle and control the recruitment of the Hsp90 clientele. In this work, we report the results of computational modeling of allosteric regulation in the Hsp90 complexes with the cochaperones p23 and Aha1. By integrating protein docking, biophysical simulations, modeling of allosteric communications, protein structure network analysis and the energy landscape theory we have investigated dynamics and stability of the Hsp90-p23 and Hsp90-Aha1 interactions in direct comparison with the extensive body of structural and functional experiments. The results have revealed that functional dynamics and allosteric interactions of Hsp90 can be selectively modulated by these cochaperones via specific targeting of the regulatory hinge regions that could restrict collective motions and stabilize specific chaperone conformations. The protein structure network parameters have quantified the effects of cochaperones on conformational stability of the Hsp90 complexes and identified dynamically stable communities of residues that can contribute to the strengthening of allosteric interactions. According to our results, p23-mediated changes in the Hsp90 interactions may provide "molecular brakes" that could slow down an efficient transmission of the inter-domain allosteric signals, consistent with the functional role of p23 in partially inhibiting the ATPase cycle. Unlike p23, Aha1-mediated acceleration of the Hsp90-ATPase cycle may be achieved via modulation of the equilibrium motions that facilitate allosteric changes favoring a closed dimerized form of Hsp90. The results of our study have shown that Aha1 and p23 can modulate the Hsp90-ATPase activity and direct the chaperone cycle by exerting the precise control over structural stability, global movements and allosteric communications in Hsp90. Source

Sanchez R.,CSIC - Institute of Materials Science | Sothmann B.,University of Geneva | Jordan A.N.,University of Rochester | Jordan A.N.,Chapman University
Physical Review Letters | Year: 2015

The thermoelectric properties of a three-terminal quantum Hall conductor are investigated. We identify a contribution to the thermoelectric response that relies on the chirality of the carrier motion rather than on spatial asymmetries. The Onsager matrix becomes maximally asymmetric with configurations where either the Seebeck or the Peltier coefficients are zero while the other one remains finite. Reversing the magnetic field direction exchanges these effects, which originate from the chiral nature of the quantum Hall edge states. The possibility to generate spin-polarized currents in quantum spin Hall samples is discussed. © 2015 American Physical Society. Source

Bridgham S.D.,University of Oregon | Cadillo-Quiroz H.,Arizona State University | Keller J.K.,Chapman University | Zhuang Q.,Purdue University
Global Change Biology | Year: 2013

Understanding the dynamics of methane (CH4) emissions is of paramount importance because CH4 has 25 times the global warming potential of carbon dioxide (CO2) and is currently the second most important anthropogenic greenhouse gas. Wetlands are the single largest natural CH4 source with median emissions from published studies of 164 Tg yr-1, which is about a third of total global emissions. We provide a perspective on important new frontiers in obtaining a better understanding of CH4 dynamics in natural systems, with a focus on wetlands. One of the most exciting recent developments in this field is the attempt to integrate the different methodologies and spatial scales of biogeochemistry, molecular microbiology, and modeling, and thus this is a major focus of this review. Our specific objectives are to provide an up-to-date synthesis of estimates of global CH4 emissions from wetlands and other freshwater aquatic ecosystems, briefly summarize major biogeophysical controls over CH4 emissions from wetlands, suggest new frontiers in CH4 biogeochemistry, examine relationships between methanogen community structure and CH4 dynamics in situ, and to review the current generation of CH4 models. We highlight throughout some of the most pressing issues concerning global change and feedbacks on CH4 emissions from natural ecosystems. Major uncertainties in estimating current and future CH4 emissions from natural ecosystems include the following: (i) A number of important controls over CH4 production, consumption, and transport have not been, or are inadequately, incorporated into existing CH4 biogeochemistry models. (ii) Significant errors in regional and global emission estimates are derived from large spatial-scale extrapolations from highly heterogeneous and often poorly mapped wetland complexes. (iii) The limited number of observations of CH4 fluxes and their associated environmental variables loosely constrains the parameterization of process-based biogeochemistry models. © 2012 Blackwell Publishing Ltd. Source

Vickers C.P.,Chapman University
Aphasiology | Year: 2010

Background: Social networks are the context for communication and life participation and are associated with adults' health, well-being, and longevity. Compared to other populations, persons with aphasia have not been included in social network research in the US. Aims: The study aimed to measure and compare 40 participants' social networks and frequency of contact within networks before and after aphasia. It also examined self-ratings of communication/social participation as well as perceived social isolation versus perceived social support. A further aim was to explore the impact of weekly aphasia group attendance on all variables by comparing two groups within the sample: 28 persons attending a weekly aphasia group, and 12 persons not attending an aphasia group. Methods & Procedures: Social network interviews for social network analysis and questionnaire surveys measured the perceptions and experiences of a non-random sample of 40 persons with aphasia in the US. Measures included Social Networks Inventory (Blackstone & Hunt-Berg, 2003), The Friendship Scale (Hawthorne, 2006), and a pilot tool, The Survey of Communication and Social Participation (Vickers & Threats, 2007). Both descriptive and inferential statistics were used to explore the data and compare the aphasia group attendees (N = 28) with non-attendees (N = 12). Outcomes & Results: Results indicated shrinkage of social networks and reduced frequency of contact with partners after onset of aphasia for the entire group. Independent samples t tests revealed significantly higher levels of social participation, and significantly less perceived social isolation and greater social connection for the 28 individuals attending a weekly aphasia group. Conclusions: A major contribution of this study is its direct inclusion of 40 individuals with aphasia in a project in the US that provided quantitative data about social networks before and after aphasia. Results confirm that clinicians should be concerned about potential reduction of social networks and social isolation after aphasia. Data also support the notion of significantly increased social participation and sense of social connectedness for those who attend aphasia groups. The findings point to the need to directly assess aphasic individuals' social networks as the context for life participation through social network analysis. It also suggests that intervention efforts in aphasia therapy would be enhanced by assessing how persons with aphasia perceive their level of social connection as well as their participation in the social environment. © 2010 Psychology Press. Source

Funk J.L.,Chapman University | Cornwell W.K.,VU University Amsterdam
Ecology | Year: 2013

The leaf economics spectrum (LES) has revolutionized the way many ecologists think about quantifying plant ecological trade-offs. In particular, the LES has connected a clear functional trade-off (long-lived leaves with slow carbon capture vs. short-lived leaves with fast carbon capture) to a handful of easily measured leaf traits. Building on this work, community ecologists are now able to quickly assess species carbon-capture strategies, which may have implications for community-level patterns such as competition or succession. However, there are a number of steps in this logic that require careful examination, and a potential danger arises when interpreting leaf-trait variation among species within communities where trait relationships are weak. Using data from 22 diverse communities, we show that relationships among three common functional traits (photosynthetic rate, leaf nitrogen concentration per mass, leaf mass per area) are weak in communities with low variation in leaf life span (LLS), especially communities dominated by herbaceous or deciduous woody species. However, globally there are few LLS data sets for communities dominated by herbaceous or deciduous species, and more data are needed to confirm this pattern. The context-dependent nature of trait relationships at the community level suggests that leaf-trait variation within communities, especially those dominated by herbaceous and deciduous woody species, should be interpreted with caution. © 2013 by the Ecological Society of America. Source

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