The Diamond long-wavelength macromolecular crystallography beamline I23 is a unique facility for solving the crystallographic phase problem, using the small anomalous signals from sulphur which are present in native protein. This is of increased importance for projects where protein labelling to introduce anomalous scatterers is proven difficult and/or expensive. A typical example is when proteins are expressed in eukaryotic cells. A nice illustration of this type of work can be seen in Rudolf AF et al, 2020 where the protein was solved by S-SAD since the seleno-methionine derivative did not express and heavy metal soaks failed.
A second benefit of the I23 long-wavelength beamline is the identification and location of lighter atoms of biological relevance such as Cl, K and Ca in crystal structures. The latter experiment is done by calculating anomalous difference Fourier maps. Practically, two datasets are collected, one below and one above the scatterer’s X-ray absorption edge, and the difference permits the anomalous scatterer identification and location. This technique was key in determining the potassium binding mode in the NaK transporter (Langan PS et al, 2018) or the location of potassium in the prokaryotic ribosome (Rozov A et al, 1019). Alternatively, this method can also be used to help model building if the starting phases are poor, i.e. a poor molecular replacement solution or partial model from experimental phases. Sulphur anomalous difference Fourier maps can be calculated to assign the methionine and cysteine side-chains and help assigning the protein sequence.
In addition to beamline access, I23 can also offers its staff expertise in data collection for anomalous phasing, structure solution and crystal structure building and refinement. We have collaborated with numerous users on difficult phasing projects providing different level of expertise depending on the user requirement.
The morphogen Sonic hedgehog inhibits its receptor Patched by a pincer grasp mechanism.
Rudolf AF, Kinnebrew M, Kowatsch C, Ansell TB, El Omari K, Bishop B, Pardon E, Schwab RA, Malinauskas T, Qian M, Duman R, Covey DF, Steyaert J, Wagner A, Sansom MSP, Rohatgi R, Siebold C. Nat Chem Biol. 2019 Oct;15(10):975-982. doi: 10.1038/s41589-019-0370-y. Epub 2019 Sep 23. PMID: 31548691
Anomalous X-ray diffraction studies of ion transport in K+ channels.
Langan PS, Vandavasi VG, Weiss KL, Afonine PV, El Omari K, Duman R, Wagner A, Coates L. Nat Commun. 2018 Oct 31;9(1):4540. doi: 10.1038/s41467-018-06957-w. PMID: 30382100
Importance of potassium ions for ribosome structure and function revealed by long-wavelength X-ray diffraction.
Rozov A, Khusainov I, El Omari K, Duman R, Mykhaylyk V, Yusupov M, Westhof E, Wagner A, Yusupova G. Nat Commun. 2019 Jun 7;10(1):2519. doi: 10.1038/s41467-019-10409-4. PMID: 31175275
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