[Conformational state of oncoprecipitin cyprein and its immunologic activity]. / Konformatsionnoe sostoianie onkopretsipitina tsipreina i ego immunologicheskaia aktivnost'.

The effect of solution ionic strength, calcium ion concentration, and temperature on spatial structure of cyprein was examined by CD, UV, and fluorescence spectroscopy. The secondary structure of the cyprein molecule was calculated from CD spectra, and the prevalence of the beta-structure (85%) was shown. An irreversible conformational transition in the range 55-60 degrees C was found, which reduces the binding activity of cyprein in interaction with carcinoembryonic antigen (CEA) and anti-cyprein antibodies. In the latter case, the binding activity was reversibly restored. Cyprein was shown to be a calcium-binding protein. Binding of calcium by cyprein and increasing the ionic strength of solution affect only tertiary structure of the protein. At an ionic strength of solution close to physiological conditions, calcium-bound cyprein shows maximum binding to CEA and anti-cyprein antibodies. It was shown by difference UV spectroscopy that cyprein does not interact specifically with the monosaccharides of the carbohydrate chains of CEA: fucose, mannose, galactose, and N-acetylglucosamine.

[Conformational stability and immunochemical properties of yersinin--a basic protein of the outer membrane of the Pseudotuberculosis microbe]. / Konformatsionnaia stabil'nost' i immunokhimicheskie svoistva iersinina--osnovnogo belka vneshnei membrany psevotuberkuleznogo mikroba.

Using spectroscopic methods (circular dichroism and intrinsic protein fluorescence) and immunoenzyme assay, changes in the spatial and antigenic structure of yersinin, porin from outer membrane of Yersinia pseudotuberculosis, were studied in solutions of ionic and non-ionic detergents at various temperatures and low pH values. Yersinin was shown to retain its secondary structure under various denaturation conditions, the content of regular structural patterns depending on specific action of the denaturation agent. Process of yersinin denaturation similarly to other membrane proteins appears to occur via two structural transitions: dissociation of oligomers and denaturation of monomers. At the first stage changes of quaternary structure accompanied by the loss of so called conformational determinants were observed. Temperature-dependent changes of monomers' tertiary structure affect antigenic activity of yersinin in a smaller degree.

[Interrelation of conformational changes of crustacin and its capacity to bind specifically with carcino-embryonic antigen]. / Vzaimosviaz' konformatsionnykh izmenenii krustatsina i ego sposobnosti spetsificheski sviazyvat'sia s rakovo-émbrional'nym antigenom.

Temperature-, ionic strength-, calcium ion- and pH-dependence of spatial structure of crustacin have been studied using CD and fluorescent spectroscopy. Secondary structure of crustacin was estimated by CD spectra. An irreversible conformational transition of crustacin's protein moiety connected with the loss of CEA-binding activity has been found at ca. 50 degrees C. Crustacin is shown to be calcium-binding protein, stability of the native crustacin conformation being markedly enhanced by calcium ions (1 mM Ca2+ shifted up the transition temperature by approximately 10 degrees C). Calcium binding and ionic strength increase led to alteration of both secondary and tertiary structures of crustacin. The highest CEA-binding activity was observed for the calcium-bond form of crustacin. A lack of specific interaction of crustacin with some saccharides was shown. Interrelation between conformation and immunochemical activity of crustacin is discussed.