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Synchrotron microcrystal native-SAD phasing at a low energy

机译：低能量的同步加速器微晶原生SAD定相

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De novo structural evaluation of native biomolecules from single-wavelength anomalous diffraction (SAD) is a challenge because of the weakness of the anomalous scattering. The anomalous scattering from relevant native elements – primarily sulfur in proteins and phospho­rus in nucleic acids – increases as the X-ray energy decreases toward their K-edge transitions. Thus, measurements at a lowered X-ray energy are promising for making native SAD routine and robust. For microcrystals with sizes less than 10 µm, native-SAD phasing at synchrotron microdiffraction beamlines is even more challenging because of difficulties in sample manipulation, diffraction data collection and data analysis. Native-SAD analysis from microcrystals by using X-ray free-electron lasers has been demonstrated but has required use of thousands of thousands of microcrystals to achieve the necessary accuracy. Here it is shown that by exploitation of anomalous microdiffraction signals obtained at 5 keV, by the use of polyimide wellmounts, and by an iterative crystal and frame-rejection method, microcrystal native-SAD phasing is possible from as few as about 1 200 crystals. Our results show the utility of low-energy native-SAD phasing with microcrystals at synchrotron microdiffraction beamlines.
机译：由于异常散射的弱点，从单波长异常衍射（SAD）对天然生物分子进行从头进行结构评估是一个挑战。随着X射线能量朝其K边缘跃迁减少，来自相关天然元素（主要是蛋白质中的硫和核酸中的磷）的异常散射增加。因此，以较低的X射线能量进行测量有望使常规SAD变得常规且稳定。对于尺寸小于10μm的微晶，由于样品处理，衍射数据收集和数据分析的困难，在同步加速器微衍射光束线上进行自然SAD相控更具挑战性。已经证明了通过使用X射线自由电子激光器对微晶进行本机SAD分析，但是需要使用成千上万的微晶才能达到必要的精度。在这里表明，通过利用在5 keV处获得的异常微衍射信号，通过使用聚酰亚胺阱，以及通过迭代的晶体和镜框抑制方法，可以从大约1 200个晶体中进行微晶本机SAD定相。我们的结果表明，在同步加速器微衍射光束线处，微晶体的低能本机SAD相控的实用性。

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