SOLUTION STRUCTURE OF ALPHA-T-ALPHA, A HELICAL HAIRPIN PEPTIDE OF DE-NOVO DESIGN

alpha t alpha is a 38-residue peptide designed to adopt a helical hair pin conformation in solution (Fezoui Y, Weaver DL, Osterhout JJ, 1995, Protein Sci 4:286-295). A previous study of the carboxylate form of a lpha t alpha by CD and two-dimensional NMR indicated that the peptide was highly helical and that the helices associated in approximately th e intended orientation (Fezoui Y, Weaver DL, Osterhout JJ, 1994, Proc Natl Acad Sci USA 91:3675-3679). Here, the solution structure of alpha t alpha as determined by two-dimensional NMR is reported. A total of 266 experimentally derived distance restraints and 20 dihedral angle r estraints derived from J-couplings were used. One-hundred initial stru ctures were generated by distance geometry and refined by dynamical si mulated annealing. Twenty-three of the lowest-energy structures consis tent with the experimental restraints were analyzed. The results prese nted here show that alpha t alpha is comprised of two associating heli ces connected by a turn region.