The aim of the proposed research is to determine the three-dimensional structure (by x-ray diffraction of single crystals) of a number of peptides (10-30 residues) that perform a variety of functions such as ion transport, analgesia, toxic, antitoxic and antibiotic by means of single crystal x-ray diffraction analysis. These crystals are composed of molecules containing light atoms only, C, N, O and H. The method of solution will be direct phase determination using the tangent formula and a variety of auxiliary formulas. Linear peptides mediating ion transport through cell membranes, particularly those in the class of peptaibophol antibiotics, are being emphasized currently. They are characterized by their length (up to 20 residues), a number of Aib residues (alpha aminoisobutyric acid) and one or more Pro residues that interfere with alpha-helix formation. The immediate goal is to establish the conformation of neighboring peptide molecules in the crystal. Structures of Leu-zervamicin in three separate crystal forms have been determined to 0.9 A resolution that give very suggestive information concerning ion channels and gating. Structure analysis has begun on antiamoebin, a related ionophore. Crystallizations are in progress for zervamicin IIB (the major component of the zervamicin family). The ultimate goal is to establish the shape and function of ion channels on an atomic scale and gating mechanisms to correlate them with measured electrical conductances. This knowledge should be very useful in the whole field of physiological ion transport through voltage dependent membranes. Further goals are to continue to establish characteristics of peptide helices, such as helix aggregation, water insertion into hydrophobic helices, facile transitions between 3(l0) and alpha-helices, bends in helices, polar surfaces on largely or completely apolar helices, all of which provide supporting information for ion transport processes. X-ray quality single crystals are on hand.
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