A method of characterization of growing of protein crystals involves the utilization of an optical imaging technique known as spatial phase imaging. The methods used heretofore have been, variously, invasive (e.g., adding a dye that is absorbed by the protein of interest), destructive (e.g., crushing protein/salt-crystal mixtures and observing differences between the crushing of salt and protein), or time-consuming (x-ray crystallography). In contrast, the present method is noninvasive, nondestructive, and rapid.
Spatial phase imaging involves the use of proprietary filters. In the present method, one uses a single camera to acquire a series of spatial phase images of a specimen [which could include one or more protein crystal(s) mixed with one or more salt crystal(s)]. One then digitally processes the image data by use of algorithms that extract information on the three-dimensional properties of the protein crystal of interest, including its volume and some aspects of its crystalline structure. This information can be processed further to extract information about the symmetry of the crystal and to detect flaws.
It is possible, in the processing of the image data, to discriminate against salt crystals or remove images of them from the scene, leaving only the protein-crystal images for analysis. To take advantage of this capability, one uses a different set of spatial phase components in algorithms developed specially for this purpose.
This method is not expected to eliminate the need for x-ray crystallography at the later stages of research on a given protein. However, as a means of identification and preliminary analysis of protein crystals, it could eliminate or greatly reduce the need for x-ray crystallography as a screening technique in the early stages. In addition to being noninvasive and nondestructive, the present method yields results so rapidly that it is suitable for real-time monitoring and, hence, for providing feedback for process control. Hence, this method is expected to accelerate the search for conditions to optimize the growth of proteins and to be a means of automation of the growth of high-quality protein crystals.
This work was done by Blair A. Barbour and Stephen Benson of Photon-X, Inc., for Marshall Space Flight Center. For further information, contact the company at (256) 740-3416.