New X-ray sources speed protein crystallography

Thirty years ago the determination of a protein structure required years of effort and typically was sufficient for a Ph.D. thesis. Today, due to advances in synchrotron X-ray sources and detectors, protein crystal structures can be calculated in just hours, “enabling many types of studies that were previously inconceivable,” according to a leading researcher at Cornell University, Ithaca, N.Y.

Sol Gruner, a Cornell physics professor and an expert in designing and building fast, large-area X-ray imaging detectors, says that high-powered synchrotron X-ray sources and advanced detectors have been largely responsible for the progress in calculating protein structures. “The biotechnological revolution of the last two decades is built upon the twin pillars of protein structure determination and genetic engineering,” he says.

Indeed, says Gruner, “Synchrotron X-radiation has become an enormously powerful tool throughout science and technology.”

Gruner presented an overview of these advances today (Feb. 16) in a talk, “Future X-ray Sources and Detector Technologies,” at the annual meeting of the American Association for the Advancement of Science in Seattle. His talk was part of a symposium, “Synchrotron Radiation as a Frontier Multidisciplinary Scientific Tool,” organized by Ernest Fontes, assistant director of the Cornell High Energy Synchrotron Source (CHESS), Doon Gibbs of Brookhaven National Laboratory and Keith Hodgson of Stanford University/Stanford Linear Accelerator Center (SLAC).

Synchrotron radiation is emitted when highly energetic electrons are deflected by magnetic fields. All existing synchrotron X-ray facilities are based on an accelerator physics technology called the storage ring. In such a ring, bunches of electrons are kept in a roughly circular orbit by magnetic deflecting and focusing structures. At Cornell, the National Science Foundation (NSF)-supported Cornell Electron Storage Ring (CESR) is the X-ray source for CHESS. Usage of synchrotron radiation has grown steadily over the past three decades as synchrotron source, X-ray optics and detector technology have steadily advanced. Gruner, who is director of CHESS, explained how novel technologies now being developed will couple with developing semiconductor X-ray detectors to open new avenues of scientific exploration.

One such new technology, which promises to remove many of the present limitations of existing storage ring X-ray sources, is based on the use of a superconducting linear accelerator (or linac) to continuously accelerate and recover the energy from an electron beam. This device, called an Energy Recovery Linac (ERL), will be able to produce X-ray beams of unprecedented brilliance and small size. Gruner is the principal investigator on a proposal to the NSF to build an ERL prototype, based on collaborative designs between Cornell and the Thomas Jefferson National Accelerator Facility, Newport News, Va.

Another future source technology, also based on linacs, is the X-ray Free Electron Laser, or XFEL. An XFEL is slated for construction at SLAC. ERL and XFEL sources, when combined with evolving solid-state X-ray detectors, Gruner said, will allow scientists to examine the structure of matter in ways previously impossible.

“This is a historically opportune time to acknowledge and celebrate the multidisciplinary nature of synchrotron radiation and discuss, in open forum, our collective views and needs for future outstanding X-ray facilities,” Gruner noted.