Radiation damage in X-ray crystallography and elemental analysis of proteins
Co-workers: Dr. Areej Abuhammad, Mr. Oliver Zeldin, Mr. Markus Gerstel,
Ms. Youngah Choi, Mr. John Bremridge
Our research focuses on developing improved methods for macromolecular crystallography (MX) to enable problems not previously accessible to structure solution to be tackled. This work currently includes studies on 100K and room temperature (RT) radiation damage and optimising strategies for in-house Sulphur and Phosphorus-SAD phase determinations.
Radiation damage (Fig 1) to the sample is an inherent problem when utilising ionising X-radiation in MX, even during cryocrystallographic (100K) data collections. We seek to understand the physical and chemical basis of the damage, and to find mitigation strategies in order to optimise our data collections and thus maximise the biological information obtained
Following our measurement of 30 MGy for the experimental dose limit for crystals held at 100K, we have investigated the RT dose limit. Surprisingly, the dose tolerated by a RT crystal is dependent on the dose rate according to a positive linear relationship. The addition of scavengers changes the RT intensity loss dependence from first to zeroth order (Fig 2) in dose.
Our method for accurately determining the concentration of trace elements bound in liquid or crystalline protein samples by proton induced X-ray emission (PIXE) is finding ongoing applications (Fig 3), and is being extended to measurements on whole cells.
- Room temperature scavengers for MX: increased lifetimes and modified dose dependence of the intensity decay. Adam I. Barker, Robert J. Southworth-Davies, Karthik S. Paithankar, Ian Carmichael and Elspeth F. Garman. J.Synchr. Radiat. (2009) 16, 205-216
- Robert J. Southworth-Davies, Melissa A. Medina, Ian Carmichael, and Elspeth F. Garman (2007) Observation of decreased radiation damage at higher dose rates in room temperature protein crystallography. Structure 15, 1341-1351
- Radiation Damage in Macromolecular CryoCrystallography Raimond B.G. Ravelli and Elspeth F. Garman Current Opinion of Structural Biology (2006) 16, 624-629
- Robin Leslie Owen, Enrique Rudiño-Piñera, Elspeth F. Garman (2006) Experimental determination of the radiation dose limit for cryocooled protein crystals. Proc. Nat. Acad. Sci (2006) 103, 4912-4917
Elspeth Garman and Geoff Grime (2005) Elemental analysis of proteins by microPIXE. Progress in Biophysics and Molecular Biology 89/2, 173-205
Figure 1: Radiation damage to an N9 neuraminidase from avian influenza, following 100K data collection at the ESRF from 3 locations on the crystal.
Figure 2: Room temperature change in form of the intensity loss dependence with dose on addition of the scavenger 1,4 benzoquinone to crystals of hen egg white lysozyme. Addition of the scavenger increases the dose tolerance by a factor of 9
Figure 3: Elemental areal concentration microPIXE maps (500µm x 500µm) obtained by scanning a 1 µm diameter proton beam in x and y across a holoferritin crystal showing: sulphur (left), iron (centre) and cadmium (right) distributions. The iron is localised in the protein crystal, while due to the presence of ammonium sulphate in the solvent, the sulphur is more spread out.