Masahiko Hiraki

Applying long wavelength X-ray （ca. longer than 2 Å） in macromolecular crystallography has been limited due to the lack of dedicated measurement environment. Photon Factory BL-1A, as an MX beamline optimized for diffraction experiment using the wavelength from 2.7 to 3.3 Å, offers the opportunity to routinely perform data collection for Native SAD phasing or light atoms identification with much sophisticated manner. Sample optimization is another key for successful experiment at the wavelength where severe absorption is inevitable. We describe how the difficulties in use of long wavelength X-ray were overcome at the beamline and the auxiliary facility, as well as the current results of Native SAD phasing.

A direct outcome of the exponential growth of macromolecular crystallography is the continuously increasing demand for synchrotron beam time, both from academic and industrial users. As more and more projects entail screening a profusion of sample crystals, fully automated procedures at every level of the experiments are being implemented at all synchrotron facilities. One of the major obstacles to achieving such automation lies in the sample recognition and centring in the X-ray beam. The capacity of UV light to specifically react with aromatic residues present in proteins or with DNA base pairs is at the basis of UV-assisted crystal centring. Although very efficient, a well known side effect of illuminating biological samples with strong UV sources is the damage induced on the irradiated samples. In the present study the effectiveness of a softer UV light for crystal centring by taking advantage of low-power light-emitting diode (LED) sources has been investigated. The use of UV LEDs represents a low-cost solution for crystal centring with high specificity.

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