Investigation of differences in the tertiary structures of food proteins by small-angle X-ray scattering

Summary With current emphasis in bioengineering on developing new and better structure-function relationships for proteins (e.g., the need for predictability of expected properties prior to cloning), practical and reliable methodology for providing characterization of appropriate features has become of increasing importance. The most potent and detailed technique, X-ray crystallography, has severe limitations: it is so demanding and time-consuming that X-ray coordinates are frequently unavailable for materials of interest; its data relate to static and essentially unhydrated structures, whereas proteins exhibit a variety of dynamic features and function in an aqueous environment; and many proteins of technological importance may never be crystallized. Small-angle X-ray scattering, however, is particularly suitable as a methodology that can provide a substantial number of significant geometric parameters consistent with crystallographic results, that can readily show tertiary structural changes occurring under varying conditions, and that can deal with solutions and gels. Results are presented here from small-angle X-ray scattering investigations of the apo and holo forms of chicken egg-white riboflavin-binding protein, chicken egg-white lysozyme, bovine milk-whey -lactalbumin and -lactoglobulin, and bovine ribonuclease. We utilize these observations to compare tertiary structures of these proteins as well as conformational changes in these structures, and to provide a basis for discussion of their physical and biological significance.Agricultural Research Service, U.S. Department of Agriculture. Reference to brand or firm name does not constitute endorsement by the U.S. Department of Agriculture over others of a similar nature not mentioned.