9604860 Schaefer The goal of the work is the characterization by solid-state NMR of proteins and DNA that are part of a supramolecular structure or assembly. These include cross-linked proteins in insect cuticle, marine organisms and plant cell walls, as well as proteins encapsulated in stabilizing lyoprotectant matrices, and DNA compacted by dendrimer-like macromolecules. Dipolar couplings between stable-isotope labels will be measured directly in these complicated biomacromolecular assemblies by REDOR (Rotational-echo double resonance) and REDOR-like NMR recoupling experiments. In the work on insect, mussel, and plant proteins, specific chemical questions will be answered as to how these structures are cross-linked and stabilized. A search will be made for new ways to stabilize fragile protein complexes in a buffered sugar glass. These matrices will then be used to examine the natural-substrate reaction intermediates of enolpyruvylshikimate 3-phosphate synthase which have been trapped in the glass. Finally, a dopant will be created for dynamic nuclear polariation experiments by burying a stable free radical in the core of an amphiphilic particle that complexes proteins and compacts DNA. REDOR will be used to characterize the local structure and the resulting distances will be used as constraints in molecular dynamics simulations designed to visualize the overall shapes of the complexes. Many biochemical and biophysical processes are carried out by or in molecular superstructures. These superstructures are macromolecular complexes or aggregates for which there is no atomic-level structural information because they are not soluble (no solution NMR) and don't crystalize (no x-ray crystallography). This work will provide specific insights into important practical problems (insect pest management, barnacle fouling of ship hulls, enzyme reaction pathways, DNA compaction) and generate a new kind of biophysical structural tool with atomic-level resolution (solid-state NMR) that is applic able to otherwise intractable systems.
