Biomolecular Materials: Structure, Phase Behavior, & Interactions

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ID: MPS/DMR/BMAT(7623) 1101900 PI: Safinya, Cyrus ORG: UC Santa BarbaraTitle: Biomolecular Materials: Structure, Phase Behavior, and InteractionsINTELLECTUAL MERIT: The aim of this proposal is to develop a fundamental understanding of the intermolecular forces and resulting structures in assemblies of filamentous proteins (in particular, neurofilaments and microtubules) derived from the cytoskeleton of neuronal dendrites and axons (the extensions used by neurons to receive and send signals to neighboring neurons). The proposal combines state-of-the-art synchrotron x-ray-scattering, x-ray-osmotic pressure, and optical and electron microscopy techniques used by the PI, and in parallel, closely related modern modeling by the co-PI. Experiments are proposed to study forces between microtubules mediated by microtubule-associated-protein (MAP) tau, an abundant unstructured biological polymer containing anionic and cationic amino acid residues, which binds to (via electrostatic interactions) and stabilizes microtubules in axons. While the precise role of MAP-tau in modulating interactions between microtubules is unclear, it is well established that aberrant interactions between tau and microtubules (e.g., due to tau mutations or over-phosphorylation) invariably lead to collapse of the cytoskeleton and neurodegeneration. Experiments are proposed to understand the structures and inter-filamentous interactions, mediated by charged neurofilament-sidearms and MAP-tau, in systems which closely mimic the distinct local environments of axons and dendrites (i.e., with different composition of the three neurofilament-sidearms and the presence or absence of MAP-tau). The specific aims of this proposal are (1) to elucidate the role of biological and synthetic multivalent counter-ions in suppressing the repulsive barrier, which prevents MAP-tau-mediated short-range attractions between microtubules, (2) to unravel the structure-function properties of MAP-tau by discovering how domain deletions (via truncated tau constructs) alter tau-mediated microtubule assembly, (3) to study the intermolecular interactions and resulting structures between neuronal cytoskeletal filaments in co-assembling mixtures of microtubules and neurofilaments, and (4) to develop quantitative models of forces between two opposing polyampholyte brushes (mimicking the structures of neurofilaments and microtubules) to closely capture the biophysics of interactions between microtubules mediated by MAP-tau, between different neurofilament-sidearms, and between neurofilament-sidearms and MAP-tau. Aside from enhancing our knowledge of the nerve cell cytoskeleton, the proposed research will further our understanding of charged-polymeric systems, a very important field of soft and biological matter, where much remains to be understood.BROADER IMPACTS: The proposed studies will lead to a comprehensive understanding of how nature makes use of competing intermolecular forces (e.g., attractions at short distances and repulsions at longer distances) to assemble distinct filamentous structures within the long extensions of nerve cells to impart critical functionalities such as mechanical stability and facilitated transport of materials. The understanding gleaned from the studies (e.g., about the specific chemical moieties responsible for inter-filament interactions) will enable the broader scientific community to employ a rational approach in the design of synthetic building-block mimics for constructing hierarchical structures arising from the built-in functionality at the molecular level that control intermolecular interactions. The biomimetic structures, in turn, are expected to have important technological applications, for example, as templates for miniaturized materials with applications in nano-biotechnology. The biomaterials research effort of the PIs is multidisciplinary and educates and trains undergraduate and graduate students and postdoctoral researchers in modern methodologies required to address important problems at the interface between physics, chemistry, engineering, and biology. The acquired interdisciplinary skills prepare the trainees for careers in academe, national laboratories, and industry. The principal investigators actively participate in UCSB Outreach Programs with the community colleges and with colleges and universities outside of Santa Barbara. The programs include the Internships in Nanosystems Science and Engineering Technology, California Alliance for Minority Participation, Research Internship in Science and Engineering, Cooperative International Science and Engineering Internships, and the Research Experience for Teachers. This activity allows the PIs to train a broad spectrum of students and teachers in multidisciplinary methods of science and engineering.