Laboratory of Molecular Biophysics Laboratory Journal 2006 X-Ray Facilities

X-ray Facilities

Ed Lowe and Elspeth Garman

Our new X-ray user facility, consisting of a 2.7 kW Bruker MicroStar X-ray generator with Montel optics on both sides, a Mar345 Imaging plate detector on the right hand side and a Bruker SMART 6000 CCD detector with 4-circle kappa goniometer on the left hand side (Figure 1), has run well this year.

Figure 1. Bruker SMART 6000 detector with 4-circle KAPPA goniometer mounted on the MicroStar generator. Also visible is the newly installed Cobra cryostat. (Click on figure for larger image).

The radiation safety requirements required to run the two sides of the new generator as independent user facilities with separate failsafe circuits were fulfilled and successfully inspected on 29 September 2005.

A Cobra liquid nitrogen-less cryostat prototype was installed on 26 October 2005 and has been operating with few problems since, including running for a period of eight weeks without interruption between August and October 2006. We have tested various nitrogen generators for Oxford Cryosystems and the system is currently being provided with nitrogen by a Parker NitroFlow generator.

A sliding base for the Mar 345 image plate in T3 was installed in November 2005. This makes access to the MicroStar anode chamber for maintenance considerably easier and the generator can now be returned to normal operation following maintenance far more quickly.

The Microstar system in T3 has run well for most of the year with few technical difficulties. The two major technical problems we have faced (an anode cooling problem [Aug 06] and a detector control fault [Oct 06]) have both been attended to swiftly by Bruker engineers.

The Microstar system is increasingly heavily used and has been used to determine a number of new structures this year. The system is increasingly being utilised to experimentally phase structures using SAD methods. Dr. Michael McDonough (Chemistry) solved the structure of the prolyl hydroxylase PHD2 one using the anomalous signal from 1 Fe, 1 I and 6 S atoms. Veronique Suavé, working with Dr. Ben Berks and Dr. Susan Lea, has solved the structure of the sulphur-oxidizing protein SoxB using the anomalous signal from a bound Mn. Structures solved by molecular replacement include the structure of CD59 by Dr. Susan Lea's group and the CH domain of actopaxin by Prof. Martin Noble's group. The system is now routinely being used to collect data for experiments such as ligand soaks and mutants of known structures. Work also continues on the use of the Microstar system for sulphur-SAD phasing. Undergraduate project students Andrew Reader (University of Oxford) and Verane Achard (University of Grenoble), working with Dr. Elspeth Garman and Dr. Ed Lowe, have proceeded to solve structures of increasing difficulty using only the anomalous signal from endogenous sulphur to provide phase information. This has culminated in the solution of the structure of glucose isomerase by S-SAD using the signal from 8 S atoms to phase this 388 residue protein (Figure 2). The manganese normally bound to GI was removed prior to crystallisation.

Figure 2. Experimentally S-SAD phased structure of glucose isomerase shown as a backbone trace with an anomalous Fourier map countoured at 9. The sulphur sites used for phasing can be clearly seen.

The T5 RU200H generator ('Myrtle', ˜134,000 hours on the clock) with a Mar345 imaging plate detector and Osmic Optics again ran very smoothly this year. The anode annual rebuild was carried out by us on September 5th. Experiments carried out on it included numerous measurements on the effects of radiation damage on protein crystals, both at room temperature and 100K by Dr. Elspeth Garman's group.

This generator was, as last year, used to inflict radiation damage for various doses on organic superconductors. The results of a collaboration between Dr. James Analytis and Dr. Arzhang Ardavan of the Correlated Electron Systems Group from the Clarendon Laboratory with Robin Owen and Elspeth Garman to investigate the effects of this damage on a copper containing organic superconductor [-(ET)₂ Cu (SCN)₂] were published in Physical Review Letters in May 2006.