Single-Crystal X-ray Diffraction Study of a Magnetically Oriented Microcrystal Array of Lysozyme

Single-crystal X-ray diffraction analysis was performed on a magnetically oriented microcrystal array (MOMA; composite in which microcrystals are oriented three-dimensionally in a polymer matrix) to demonstrate its potential to determine protein structure from a powder sample. Recrystallized hen egg-white lysozyme was pulverized to prepare a microcrystalline powder as a model system from which a MOMA was prepared. The microcrystalline powder was suspended in an ultraviolet (UV)-curable monomer and rotated nonuniformly in a static magnetic field (8 T), and then, the crystalline alignment was consolidated by UV light irradiation. The obtained sample was subjected to conventional single-crystal X-ray diffraction measurement. The structure determined for the MOMA was found to belong to the space group P2(1)2(1)2(1) with unit-cell dimensions a = 51.26, b = 59.79, and c = 29.95 angstrom, in agreement with the structure of the single crystal from which the MOMA was prepared. The protein structure was refined at the highest resolution of 3.0 angstrom, which agreed with that determined with an independently grown single crystal under comparable conditions. The fabrication method presented here provides a powerful means of determining the structure of proteins that do not crystallize to sizes suitable for conventional single-crystal X-ray analyses.