The effect of solution ionic strength, calcium ion concentration, and
temperature on spatial structure of cyprein was examined by CD, UV, an
d fluorescence spectroscopy. The secondary structure of the cyprein mo
lecule was calculated from CD spectra, and the prevalence of the beta-
structure (85%) was shown. An irreversible conformational transition i
n the range 55-60 degrees C was found, which reduces the binding activ
ity 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 s
olution affect only tertiary structure of the protein. At an ionic str
ength of solution close to physiological conditions, calcium-bound cyp
rein shows maximum binding to CEA and anti-cyprein antibodies. It was
shown by difference UV spectroscopy that cyprein does not interact spe
cifically with the monosaccharides of the carbohydrate chains of CEA:
fucose, mannose, galactose, and N-acetylglucosamine.