Fine-needle capillary mounting for protein microcrystals

Protein microcrystals of less than 10 µm in size are now applicable to X-ray studies by synchrotron microbeam technology. However, because of their small size, they are difficult to handle and mount. In addition, the deterioration of data quality by scattering from the mounting apparatus and crystallization solvent is not negligible. To address these issues, a simple mounting method is proposed using a fine-needle capillary similar to that used for microinjection in cell biology. In this method, microcrystals are pulled up by capillary action or pipetting, and are held at the tip together with a small amount of cryoprotectant. The quality of the diffraction data using this method is comparable to that of data from conventional cryoloops. This solid apparatus is hopefully suitable for automation of microcrystal handling coupled with optical tweezers.