New techniques in fast time-resolved structure determination.

New techniques in fast time-resolved X-ray crystallography provide a different approach to understanding the structural basis of protein function. Two biological systems have been studied as part of the refinement of these techniques, and have actually spurred new ideas in time-resolved structural studies. The dissociation of carbon monoxide from carbon-monoxy myoglobin has earlier been investigated over a time range spanning 18 orders of magnitude (femtoseconds to hours) using spectroscopic methods. Rapid time-resolved determination of the entire myoglobin structure made it possible to determine both the position of the CO after photodissociation and the entire globin structure, over a time range from nanoseconds to milliseconds, during which the heme and globin relax and the carbon monoxide rebinds. Photoactive yellow protein, a relative newcomer to biophysical research, has a fully-reversible photocycle containing several spectrally distinct intermediates. Identifying and solving the structures of each intermediate is the initial goal in time-resolved studies on this protein and will contribute to a greater understanding of the biological process of light driven signal transduction.