Crystal structures of vancomycin-related glycopeptide antibiotics

C-257 most of the amino acids in gramicidin A show a statistical preference for~ confom1ation, that preference in tyrosine is highest and significantly greater than that of tryptophan.Apparently as a result of the tight coiling, the \jf,¢ values of the L residues in the structures are in a sparsely populated region of the Ramachandran plot, while the D-residues are in the most densely populated region corresponding to ~-sheet geometry.The properties of the gramicidin heterodimer may relate to analogous properties of p!ion.The enigmatic behavior of prions, the protein responsible for diseases such as scrapie in animals and kuru and Creutzfeldt-Jakob disease in humans, has been attributed to the presence of trace amounts of mutants that induce heterodimer fmmation or another type of aggregation.