Molecular close-packing method and its application to crystal structure determination of deshexapeptide (B25-B30) insulin.

Based on the molecule-packing theory, we defined a molecule-packing function expressing the compatibility of packing among the symmetry-related molecules in a unit cell. A computer program imitating the close-packing of molecules in the objective crystal lattice and giving the function value of each rotation and translation of the molecule in the unit cell was performed, and it therefore made the close-packing of molecules express quantitatively. This method not only could judge a correct solution from several peaks of the rotation or translation function but it may also independently, quantitatively and quickly solve some specific problems of rotation and translation. Using known structure of despentapeptide (B26-B30) insulin as an example, the effectiveness of this method and its program was inspected, and this method was successfully applied to solving the translation problem of the unknown structure of deshexapeptide (B25-B30) insulin. The molecular close-packing method proved by the results of R-search and electron density maps is relatively independent of the molecular replacement method, though an effective complement of it.