SMALL-ANGLE X-RAY-SCATTERING STUDY ON CEL-III, A HEMOLYTIC LECTIN FROM HOLOTHUROIDEA CUCUMARIA-ECHINATA, AND ITS OLIGOMER INDUCED BY THE BINDING OF SPECIFIC CARBOHYDRATE

Hemolytic lectin GEL-III from a marine invertebrate Cucumaria echinata forms an oligomer upon binding of specific carbohydrate such as lacto se at high pH values and in the presence of high concentrations of sal t. In this study, using small-angle X-ray scattering, we characterized CEL-III and its oligomer induced by the binding of lactose, The molec ular mass of the oligomer was determined as 1019 kDa from its forward scattering value, compared with 47 490 Da for the monomer, This oligom er size is much larger than that estimated using SDS-polyacrylamide ge l electrophoresis (SDS-PAGE, 270 kDa), The monomer has a 24.6 Angstrom radius of gyration and can be approximated by a rod which has a 20 An gstrom radius and a height of 75 Angstrom, while the oligomer has a 10 1.4 Angstrom radius of gyration. Together with the comparison of the r adii of gyration and the forward scattering of the cross-section of th e monomer and oligomer, it is suggested that in aqueous solution the o ligomer comprises three or four molecules of a smaller unit which was observed by SDS-PAGE (270 kDa), held by a relatively weak interaction, The scattering profile also suggests that the oligomer has a hole in its central axis which might be associated with the formation of ion-p ermeable pores in the erythrocyte membrane by CEL-III during the hemol ytic process. (C) 1997 Federation of European Biochemical Societies.