ブックタイトル日本結晶学会誌Vol60No5-6

概要

日本結晶学会誌Vol60No5-6

日本結晶学会誌60，233-239（2018）世界の放射光施設を使ってみよう（1）The Long-wavelength MacromolecularCrystallography I23 at Diamond LightSource＊Diamond Light Source, Harwell Science and Innovation Campus＊＊Research Complex at Harwell, Harwell Science and Innovation CampusArmin WAGNER＊,＊＊, Ramona DUMAN＊,＊＊,Kamel el OMARI＊,＊＊, Vinay GRAMA＊andVitaliy MYKHAYLYKH＊Long-wavelength macromolecular crystallography（MX）has beenproposed for a long time as a tool for phasing novel macromolecularcrystal structures without additional heavy atom labelling. Making useof anomalous diffraction from atoms natively present in the crystal,such as sulphur and phosphorus, has become increasingly popular overthe past years. Nevertheless, the full potential of this technique, has notbeen fully exploited due to lack of dedicated experimental setups ableto easily access wavelengths longer than 2 A. Since the wavelengths forthe?absorption?edges?of?sulphur?and?phosphorus?are?significantly?longer,?standard beamline setups are not suitable to provide high-quality, highresolutiondata, as the experiments are limited by the increasing absorptioneffects and the diffraction angles for longer wavelengths. Currently onlytwo synchrotron beamlines offer access to optimised sample environmentsusing wavelengths longer than 2.7 A：BL1A at Photon Factory, Japan andI23 at Diamond Light Source, UK. Here, we describe the challenges andsolutions implemented at the in-vacuum long-wavelength MX beamlineI23?and?present?first?results.1．IntroductionMacromolecular crystallography is the most successfultechnique in structural biology, contributing to date morethan 130,000 structures to the total 145,000 structures in theprotein data bank. The success of this technique is owed tothe significant investment in automation of all aspects ofthe structure determination pipelines, from cloning, proteinexpression and purification, crystallisation, automatedsample changing and data collections, all the way through toautomated processing and phasing. Recently, Grimes et al. 1）reviewed these developments at Diamond Light Source withan outlook towards the future of MX.The majority of MX experiments are nowadays performedat synchrotron beamlines, typically at wavelengths around1 A. The wavelength is an important parameter to selectin an MX experiment and synchrotron beamlines typicallycover a range from 0.7 to 2.0 A. For crystal screening and日本結晶学会誌第60巻第5･6号（2018）high resolution data collections,λ＝1 A is a good comprisebetween diffraction and detector efficiency of Si based pixelarraydetectors. Tuning the wavelength also allows exploitinganomalous dispersion, a resonance effect observed close tothe characteristic absorption edges from elements present inthe crystal structure. Three main applications exist to exploitthe anomalous contrast in MX when tuning the wavelengthclose and across absorption edges: element identification,location of sulphur positions to assist model building andexperimental phasing.To identify particular anomalously scattering elementsin the electron density, typically two data sets are needed,one above the absorption edge（higher energy or shorterwavelength side）and a second one below（lower energyor longer-wavelength side）. Atoms from the element underinvestigation will show peaks in anomalous differenceFourier maps calculated from the data above the absorptionedge, which are not present below the edge（or significantly233