MASSHA - a graphics system for rigid-body modelling of macromolecular complexes against solution scattering data

A program, MASSHA, for three-dimensional rendering and rigid-body refinemen t is presented. The program allows display and manipulation of high-resolut ion atomic structures and low-resolution models represented as smooth envel opes or ensembles of beads. MASSHA is coupled with a computational module t o align structural models of different nature and resolution automatically. The main feature is the possibility for rigid-body refinement of the quate rnary structure of macromolecular complexes. If high- or low-resolution mod els of individual subunits are available, the complex can be constructed on the computer display and refined to rt the experimental solution scatterin g data. MASSHA provides both interactive and automated refinement modes to position subunits in a heterodimeric complex (general case) and in a homodi meric complex with a twofold symmetry axis. Examples of application of the program (running on IBM PC compatible machines under Windows 9x/NT/ 2000) a re given.