GEOM: a new tool for molecular modelling based on distance geometry calculations with NMR data.

GEOM is a new graphics tool which allows the use of distance geometry to compute linear and cyclic structures typically arising in drug design situations. Modified amino acids or monomeric organic entities can be easily constructed in an interactive way and deposited in the library of the distance geometry program together with geometric information required for structure calculation in dihedral angle space. In addition, GEOM is able to produce all files needed to calculate a structure based on NMR data (NOE and J-coupling constraints) and it permits the graphic analysis and comparison of computed structures. The application of GEOM is demonstrated in three examples: modelling of cyclosporin A structures with and without a limited set of H-bond constraints and modelling of a cyclic hexapeptide with a full NMR data set.