Alpha-helix structure of parathyroid hormone fragment (1-34) predicted by Monte Carlo simulated annealing.

Tertiary structure of parathyroid hormone fragment (1-34) is predicted by the Monte Carlo simulated annealing method. Among the 20 structures obtained after completely unbiased calculations, the lowest-energy conformation exhibits two alpha-helices around residues 2-10 and 18-22. This structure agrees with the models, especially with the location of helices, deduced from experiments. In addition, the simulation supports empirical implications in the following two points. (1) The helix near the N-terminus is more stable than the C-terminal one. (2) The rest of the peptide segments are flexible and do not tend to have any definite structure. Our calculation correctly predicts only an alpha-helix, whereas previous analyses by the Chou-Fasman method leave an ambiguity between an alpha-helix and a beta-strand.