Improving the diffraction quality of MTCP-1 crystals by post-crystallization soaking

Significant improvement in the resolution and quality of the X-ray diffraction of crystals of MTCP-1 protein was observed on post-crystallization soaking. The MTCP-1 crystals grown from 1.5 M ammonium sulfate diffracted to only 3.0 Angstrom resolution with some disorder in the diffraction. After post-crystallization soaking in a solution containing 2.0 M ammonium sulfate, the disorder was eliminated and diffraction extended to better than 2.0 Angstrom resolution. Both native and selenomethionine-enriched crystals demonstrated better diffraction after soaking for several months. This simple technique may be useful to improve the diffraction quality of protein crystals generally.