Marco Colombini - US grants

9701591 Palmer Stream environments are difficult to fully understand because food and living space tend to be distributed in an uneven way, and animals move extensively within the environment. These are factors which have lately received much attention separately, but not together. In particular, many theoretical studies assume either that animals move at random, or that they have perfect knowledge of their environment, and thus can determine the best location to move to. However, many animals do not fit these simplified ideas-they can control their movements to some extent but do not have extensive information about their environment. The investigators will use computer models, with varying levels of biological realism, to determine how animals move within the uneven stream environment, and how their movement affects population sizes and stability. They will also perform experiments in an artificial stream to determine how much control small stream invertebrates can exert over their movement in the face of flow. The movement patterns and population levels of small stream invertebrates have important consequences for the stream environment, because they form the base of the stream food web and are involved in the microbial processes web as well.

9817348
Kaufman
This grant provides partial support for the purchase of a gas source stable isotope mass spectrometer with automated preparation systems for the Isotope Geochemistry Laboratory at the University of Maryland. The Principle Investigators include: A.Jay Kaufman, a recent addition to the Department of Geology faculty after seven years as a post-doctoral fellow and research scientist in stable isotope geochemistry at Harvard University; Karen Prestegaard, a physical and chemical hydrologist in the Department of Geology; and Margaret Palmer, an ecologist in the Department of Zoology. In addition, Christina Gallup, a geochronologist and coral researcher in the Department of Geology, and Russ Dickerson, an atmospheric chemist in the Department of Meteorology will use the new instrumentation in their studies.

The establishment of a gas source stable isotope mass spectrometer at the University of Maryland represents the first academic facility of its kind in the Washington D.C. area. As such, this facility will allow additional collaborative studies by local researchers, in particular at George Washington University and the Smithsonian Institution. The gas source instrument will be housed in a newly-renovated laboratory adjacent to the existing stable isotope preparation laboratory in the Chemistry building. This facility, funded by the university and the Earth Sciences Instrumentation and Facilities Program (EAR/IF), will support research initiatives in chemical stratigraphy, carbonate geochemistry, global climatic and environmental change, coral research, hydrology, atmospheric and environmental sciences.
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Transmembrane channels are involved in many cellular processes, such as transport of metabolites, proteins and transcription factors through biological membranes. It is evident that the ability of large channels to permeate small ions does not necessarily reflect their ability to allow larger ions or macromolecules to cross the membrane. However, the same basic electrophysiological techniques, initially developed for studies of ion-selective channels, are routinely applied to all groups of channels. A new approach was developed that opens the possibility to monitor channel permeability for virtually any molecule. The method allows measurement, at the single channel level, of the transport of relatively high molecular weight molecules such as metabolites and macromolecules in the presence of small permeant ions. This is potentially a very general method and should be applicable to measuring the permeation of a wide-range of physiologically important solutes through a variety of different channels. By using the mitochondrial channel, called VDAC, it is intended to show that while the channels with large pores are poorly selective for small ions, they may show high selectivity for the larger molecules they evolved to transport. The new approach will be used to measure the partitioning of metabolites into the channel and their mobility within the channel. This is achieved by analyzing the change in average current and current noise produced when these metabolites now through a single channel and thus obstruct the passage of the smaller ions. Preliminary evidence demonstrates that VDAC selects among metabolites based on their 3-dimensional structure, not merely size and charge. ATP permeates the pore, but a glutamate tetrapeptide with similar size and charge does not. The nature of this selectivity will be examined by using other molecules whose physical properties resemble those of ATP. In addition, the importance of charge distribution within the pore that favors ATP permeation over other molecules will be verified. A panel of site-directed mutants will be used. To explore the possibility that this selectivity is a conserved property, VDAC channels isolated from very different species will be analyzed. Different VDAC isoforms within the same organism will be examined to determine whether they exhibit different selectivity patterns reflecting their specialized functions. Furthermore, apocytochrome c permeation will be studied in order to determine whether small proteins might be able to go through VDAC. If successful, this work will gain needed insight into the transport characteristics of large channels to develop ideas about their metabolite selectivity.

The ability of living organisms and individual cells to compartmentalize is critical to life. This compartmentation allows each region to maintain an environment especially tuned to the function it serves. Proteins called channels aid in this compartmentation by allowing selected molecules and ions to cross the barriers between the compartments, the membranes. This project explores the hypothesis that channels that allow the passage of large molecules do so in a highly selective way. This differs from the current presumption that these larger pathways are nonselective. The research can be pursued thanks to the development of a new method to both detect and quantitate the passage of larger molecules through the pathways formed by channels. The interference of the flow of small ions by the larger molecules is measured. If successful, this research will change the way we think about the role of large channels in the lives of cells.

In many ecosystems, the dominant habitat patches frequently change in terms of their overall quality or their resource levels. Periodically, habitat patches may be physically disrupted or destroyed. In such highly dynamic systems it often is assumed that mobile fauna will be unresponsive to the arrangement of habitat patches or to other landscape attributes. The underlying logic is that faunal responses to landscape attributes will be masked by the spatial and temporal variability of such systems. In this proposal, we argue that mobile fauna in highly dynamic systems are, in fact, responsive to landscape attributes - especially patch arrangement. Population persistence and species interactions following the disruption of patches or changes in resources may be influenced greatly by the quality and arrangement of patches. In prior NSF-funded research, we found that stream-dwelling chironomids and copepods respond to the quality and distribution of habitat (leaf) patches in laboratory and field experiments, but we did not consider how patch stability, patch resource (leaf species) composition, or predator-prey interactions influence faunal dynamics. Here, we hypothesize that invertebrate abundance in streambeds is better explained at the scale of multiple patches (the "landscape") than at the scale of individual patches; is directly linked to the interactive effects of patch arrangement, patch stability, and patch quality; and, that invertebrate response to these three factors is modified by the presence of fish predators.

We propose three field experiments to test the following specific hypotheses: (1) in stable landscapes (no patch movement), the abundance of stream invertebrates depends on patch arrangement and patch quality (leaf species composition); (2) when patches are not stable, the abundance of invertebrates depends on the interactive effects of patch arrangement and the level of patch stability; and (3) the response of stream invertebrates to patch arrangement, quality, & stability is influenced by the presence of predatory fish. To test the first two hypotheses, we will manipulate patch arrangement and patch stability or leaf quality using repeated measures factorial designs. For the third hypothesis, we will manipulate predator abundance and one landscape attribute at a time (patch arrangement, patch stability, or leaf quality). We will follow changes over time in the abundance of invertebrates at the level of landscapes, although we also will be able to assess variability within and among the individual patches that constitute each landscape.

This work has important implications because we are asking if and how changes in landscapes --in terms of patch types and their arrangement and their resource levels -- influence biotic assemblages. Much of the current understanding of biotic responses to spatial landscape features is based primarily on theoretical and empirical work on systems in which the landscape features are fairly stable. Since many systems are highly dynamic -- patches move and patch quality varies temporally -- the type of research proposed here is greatly needed. As in our past grant, this research will be conducted as a collaborative effort between P. Silver at Penn State Erie, an undergraduate institution, and M.A. Palmer at University of Maryland College Park, a large research institution. The PI's, undergraduates, graduate students and a post doctoral associate will collaborate in all phases of the work, thereby providing maximum opportunity for students to participate in high quality research in an atmosphere of intense teamwork and collaboration with workers at a large research campus and a small primarily teaching campus.

Intellectual merit. Membranes compartmentalize the cell interior and separate each cell from its environment. The general dogma is that proteins form the transport pathways by which specific molecules are translocated across these membranes. However, a naturally-occurring lipid, ceramide, has also been shown to form large channels capable of translocating proteins across membranes. This coincides with ability of ceramide to initiate a form of programmed cell death called apoptosis. A key step in this process is the release of proteins from mitochondria, likely through ceramide channels. Proteins known to regulate the protein release (members of the Bcl-2 family) also regulate ceramide channels. The proposed research is to understand how proteins control ceramide channels. Since much evidence suggests that ceramide channels are rigid structures, highly cross-linked by hydrogen bonding, a working hypothesis is that proteins bind to the channel causing a structural change that ripples through the entire structure to form the channel. This and other hypotheses will be tested using both kinetic and thermodynamics approaches and microfluidics. In addition, the interactions between the proteins and ceramide channels will be probed by mutations in the protein and the use of chemical analogs of ceramide. These complementary experiments will yield insights into the novel regulation of lipid macrostructures by proteins and will link biophysical and mechanistic understanding of cell biological function. This research will also add to our understanding of the extremely important cellular process of apoptosis.

Broader impacts: The work has and will continue to involve the training of students at the high school, undergraduate, graduate, and post-doctoral levels. Typically five to seven undergraduates (majoring in engineering, chemistry or biology) and one summer student from a local high school will work closely with the principal investigator. The research has also greatly influenced the teaching of the investigator. His growing recognition of the importance of understanding the underlying physics of biology has led him to advocate for a radical change in the teaching of physics to undergraduate life science majors. As a pilot project, the PI will continue to teach an honors course entitled 'Physics of Living Systems' as part of a new physics curriculum, which will be expanded during the project period.