I. Usón and G.M. Sheldrick
Institut für Anorganische Chemie, Universität Göttingen, Tammannstr. 4, 37077 Göttingen, Germany
Keywords: direct methods, ab initio, stucture solution, real/reciprocal space iteration
Ab initio structure solution based on real/reciprocal space iteration with the 'half-baked' method[1,2] (inspired by Shake & Bake[3], but different in detail) will be illustrated by the solution of previously unknown structures which were not amenable to conventional methods despite exhaustive solution attempts. Ways to improve the starting random phases using general chemical knowledge that lead to an improved success rate of the method will be discussed.
Hirustasin, a 55 amino acid serine protease inhibitor containing 5 disulphide bridges can be solved with either 1.2 A low temperature data, or with 1.4 A room temperature data. Crystals belong to the space group P43212. (Data collected by Peer Mittl and Stefania di Marco)
A cycloamilose composed of 26 glucose residues, with two molecules in the P1 cell, containing a total of 572 carbohydrate atoms plus 147 solvent sites, could be solved with data to 1.1 A (collected by Katrin Gessler).
[1] Sheldrick G.M.: SHELX applications to
macromolecules, in "Direct methods for solving
macromolecular structures. Proceedings of the NATO advanced study
institute on direct methods for solving macromolecular structure.
Kluwer Academic Publishers. Ed. Suzanne Fortier 401-411 (1998).
[2] Sheldrick G.M., Gould R.O.: Structure Solution by iterative
peaklist optimization and tangent expansion in space group P1, Acta
Cryst. B51:423-431 (1995).
[3] Miller R., DeTitta, G.T., Jones, R., Langs, D.A., Weeks, C.M.
& Hauptman, H.A.: On the application of the minimal principle
to solve unknown structures. Science. 259:1430-1433
(1993).