Low-resolution real-space envelopes: the application of the condensing-protocol approach to the ab initio macromolecular phase problem of a variety of examples

A recently reported method - the improved condensing protocol [Subbiah (1991). Science, 252, 128-133; (1993). Acta Cryst. D49, 108-119] - for obtaining low-resolution macromolecular envelopes is applied to five varied test cases. These examples were chosen to illustrate the general applicability of the method to the wide range that typical macromolecular crystals adopt. The cases include small and large asymmetric unit volumes (4.7 × 10⁴ to 1.17 × 10⁶ Å³), low and high symmetry (2 to 12 symmetry elements), small and large proteins (1570 to 12 216 non-H atoms), orthogonal and non-orthogonal unit cells, a wide variety of space groups (P2₁ to P6₃22), small and large solvent contents (33-80%), and a case of non-crystallographic symmetry (threefold). In all five cases the inherent ambiguity of the condensing protocol in differentiating between bulk matter and bulk solvent is then resolved by use of the recently reported sign-fixing method (Subbiah, 1993).