The present invention provides crystalline forms of a human IgG Fc variant comprising one or more amino acid residues that provides for enhanced effector function, methods of obtaining such crystals and high-resolution X-ray diffraction structures and atomic structure coordinates. The present invention also provides machine readable media embedded with the three-dimensional atomic structure coordinates of the human IgG Fc variant and methods of using them. The present invention also provides human IgG Gc variants with reduced binding to at least one Fc?R.
