Extending Ab Initio Phasing up to 2.2 Å Resolution: New Superposition Techniques

Patterson superposition techniques are a historical method for solving the structures of small molecules ab initio, provided they contain heavy atoms in the unit cell. In the 1990s, they werecombined with effective EDM procedures and succeeded in the crystal structure solution of macromolecular structures with resolution data up to 1.6-1.9 Å. In this paper we enlarge the concept of Patterson superposition by replacing it with the vector superposition concept. We show, indeed, that besides Patterson other Fourier syntheses may also be used for the superposition of the interatomic vectors. Five Fourier syntheses are described and used in the practical applications. We show that even macromolecular structures with 2.2 Å data resolution may be solved via the new approach.