Frontiers in Bio-Metals: Probing Metal Ions in Biology with X-ray Absorption Spectroscopy Royal University Hospital, Mall Lecture Theatre University of Saskatchewan, Saskatoon, Saskatchewan, Canada May 11, 2005

Background

The Canadian Light Source or "Synchrotron" is Canada's biggest science project in more than three decades. The research capabilities enabled by this state-of-the-art facility are expected to positively impact almost all fields of scientific research in Canada. X-ray absorption spectroscopy is one of the most important tools available through the Canadian Light Source. To find out how the availability of this technique might benefit your research or research in your field, come to the workshop at the University of Saskatchewan on May 11, 2005. The workshop will be focused on Bio-Metals, but the information reviewed will be applicable to a wide range of scientific disciplines.

1. Metals in Intact Tissues

Biomedical and biological applications of X-ray absorption spectroscopy (XAS) to intact tissues are still relatively new and few in number. The technique has previously lacked the sensitivity to answer most questions in this area, but recent developments in synchrotron light technology mean that physiologically relevant levels are now feasible in many cases. Significant  progress in biomedical/biological XAS is expected in the near future, and with the new facilities at the Canadian Light Source, Canada has the potential to be at the forefront of this emerging field.

XAS can probe intact tissues, in principle non-destructively, and obtain biochemical information about a target element wherever it occurs within complex systems. Examples of samples which might be studied include cell cultures, tissue fragments, or even intact (small) organisms.

Two fundamentally different types of measurement can be made - bulk XAS where a relatively large X-ray beam interrogates the whole sample, and XAS imaging where a microscopic beam is used to build up images or maps of the different chemical species of a particular element. Bulk XAS has the best sensitivity, but XAS imaging has obvious advantages in developing a biochemical understanding of biometals in whole tissues.

2. Metals in Biological Molecules

The use of Extended X-ray Absorption Fine Structure (EXAFS) to obtain detailed structural information about metals in purified biological molecules was one of the very first applications of X-ray absorption spectroscopy. Today EXAFS is a well-developed technique and continues to provide valuable detail about metals in proteins. EXAFS targets a specific element within the molecule (e.g. Fe, Cu, Zn or Mo) and yields radial structural information. This includes the number of ligands coordinating the metal, information on the type of ligands, and in particular a very accurate measure of the interatomic distances (better than ±0.02Å). EXAFS of metalloproteins provides complementary information to that obtained from protein crystallography and NMR spectroscopy, and can be used on solutions without special treatment or crystallization procedures.

New experimental directions for EXAFS of metalloproteins include the following:

High-resolution (in interatomic distances): Although EXAFS has excellent accuracy for bond-length determination, the resolution is less impressive. If a central atom has two ligands at slightly different interatomic distances, the limit in resolution of these distances depends on how far in energy the EXAFS extends. Recent advances in stability of beamlines have allowed workers to scan to unprecedented energy ranges, yielding much improved resolution. This allows a more detailed determination of the active site structure and enables important insights into structure-function relationships.

Low concentrations: Until recently, 1 mM was the accepted lower concentration limit for good quality EXAFS. Modern high-flux beamlines, combined with state of the art detectors, are now facilitating measurements at much lower concentrations. 

The Canadian Light Source will provide the first facilities for X-ray absorption spectroscopy in Canada, with state-of-the-art detectors, helium cryostats, and facilities for XAS imaging. Come to the workshop "Frontiers in Bio-Metals: Probing Metal Ions in Biology with X-ray Absorption Spectroscopy" on May 11 at the University of Saskatchewan, Saskatoon, Canada and find out how your science could be impacted by exciting new developments in this field.

Support for this workshop is provided by the Canadian Light Source and by the Saskatchewan Health Research Foundation.

Last modified: 2012-01-31 16:01:17