Acerbo Alvin Samuel, Cook Michael J, Gillilan Richard Edward
Macromolecular Diffraction Facility of the Cornell High Energy Synchrotron Source (MacCHESS), Cornell University, 161 Synchrotron Drive, Ithaca, NY 14853, USA.
J Synchrotron Radiat. 2015 Jan;22(1):180-6. doi: 10.1107/S1600577514020360. Epub 2015 Jan 1.
X-ray scattering of biological macromolecules in solution is an increasingly popular tool for structural biology and benefits greatly from modern high-brightness synchrotron sources. The upgraded MacCHESS BioSAXS station is now located at the 49-pole wiggler beamline G1. The 20-fold improved flux over the previous beamline F2 provides higher sample throughput and autonomous X-ray scattering data collection using a unique SAXS/WAXS dual detectors configuration. This setup achieves a combined q-range from 0.007 to 0.7 Å(-1), enabling better characterization of smaller molecules, while opening opportunities for emerging wide-angle scattering methods. In addition, a facility upgrade of the positron storage ring to continuous top-up mode has improved beam stability and eliminated beam drift over the course of typical BioSAXS experiments. Single exposure times have been reduced to 2 s for 3.560 mg ml(-1) lysozyme with an average quality factor I/σ of 20 in the Guinier region. A novel disposable plastic sample cell design that incorporates lower background X-ray window material provides users with a more pristine sample environment than previously available. Systematic comparisons of common X-ray window materials bonded to the cell have also been extended to the wide-angle regime, offering new insight into best choices for various q-space ranges. In addition, a quantitative assessment of signal-to-noise levels has been performed on the station to allow users to estimate necessary exposure times for obtaining usable signals in the Guinier regime. Users also have access to a new BioSAXS sample preparation laboratory which houses essential wet-chemistry equipment and biophysical instrumentation. User experiments at the upgraded BioSAXS station have been on-going since commissioning of the beamline in Summer 2013. A planned upgrade of the G1 insertion device to an undulator for the Winter 2014 cycle is expected to further improve flux by an order of magnitude.
溶液中生物大分子的X射线散射是结构生物学中越来越受欢迎的工具，并且从现代高亮度同步辐射源中受益匪浅。升级后的麦克斯生物小角X射线散射站现位于49极摆动器光束线G1处。与之前的光束线F2相比，通量提高了20倍，使用独特的小角/广角X射线散射双探测器配置，可实现更高的样品通量和自主X射线散射数据采集。这种设置实现了从0.007到0.7 Å(-1)的组合q范围，能够更好地表征较小的分子，同时为新兴的广角散射方法提供了机会。此外，正电子储存环升级为连续注入模式，提高了光束稳定性，并消除了典型生物小角X射线散射实验过程中的光束漂移。对于浓度为3.560 mg/ml的溶菌酶，单次曝光时间已缩短至2 s，在吉尼埃区域的平均品质因数I/σ为20。一种采用低背景X射线窗口材料的新型一次性塑料样品池设计，为用户提供了比以前更纯净的样品环境。与样品池结合的常见X射线窗口材料的系统比较也已扩展到广角范围，为不同q空间范围的最佳选择提供了新的见解。此外，该站还对信噪比水平进行了定量评估，以便用户估计在吉尼埃区域获得可用信号所需的曝光时间。用户还可以使用一个新的生物小角X射线散射样品制备实验室，该实验室配备了基本的湿化学设备和生物物理仪器。自2013年夏季光束线调试以来，用户一直在升级后的生物小角X射线散射站进行实验。计划在2014年冬季将G1插入装置升级为波荡器，预计通量将进一步提高一个数量级。
