High Resolution Macromolecular Crystallography

摘要

Atomic resolution is achieved when diffraction data extend beyond 1.2 A. Structure refinement at this resolution allows anisotropic ADPs, reliable interpretation of static disorder, solvent structure and H atoms. Stereochemical restraints can be relaxed or removed, providing unbiased high-quality information about macromolecular stereochemistry, which in turn can be used to define improved conformation-dependent libraries. The surplus of data allows estimating least-squares uncertainties in the derived parameters, analogously to small-molecule standards. Atomic resolution data provide the most reliable information about macromolecular structure, especially important for validating new discoveries or resolving subtle issues of molecular mechanisms. At ultrahigh resolution it is possible to study charge density distribution by multipolar refinement of electrons in non-spherical orbitals. The current limit for macromolecular crystal X-ray diffraction is 0.55 A for nucleic acids (Z-DNA) and 0.48 A for proteins (crambin).