We propose new solid-state NMR experiments to determine the structure and dynamics of noncrystallizeable proteins which have been immobilized in or on cell-wall surfaces. The versatile REDOR and TEDOR analytical methods that we have developed in the last five years for the accurate determination of internuclear distances (and hence geometry and structure) of freeze-quenched lyophilized protein complexes, and proposed new combined TEDOR-REDOR and TEDOR-TEDOR experiments, are heteronuclear techniques that are directly applicable to cell-wall protein problems. The sensitivity of solid-state NMR for this kind of work already has been established in practical applications on big proteins. We now routinely perform long-range distance measurements on one micromole of a 50-kD labeled protein complex. We propose specific new REDOR/TEDOR solid-state experiments to characterize: (l) magainin peptide antibiotics in multilamellar lipid dispersions; (2) peptidoglycan bridges in intact cell walls of S. aureus; (3) protein-oligosaccharide complexes at cell-cell interfaces; (4) the interfacial site of phospholipase A2 complexes in a hydrated bilayer; and (5) the lipid-binding region of D-lactate dehydrogenase. Structural results from the protein-oligosaccharide experiments will be complemented by direct imaging of the complexes using non-contact atomic force microscopy. All of these practical applications could lead both to new science and new biotechnology, the latter including the use of solid-state NMR to assist in the biorational design of drugs and antibiotics.
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