CRYSTALS OF FAB+hCG COMPLEX AND FABS
M.A. Dingwall and N. W. Isaacs
Department of Chemistry, Joseph Black Building, University of Glasgow, G12 8QQ, U.K.
hCG, MW ~40kDa, is a member of the family of Glycoprotein Hormones which includes; Luteinizing Hormone, Follicle Stimulating Hormone, and Thyroid Stimulating Hormone. All are glycosylated, and are also members of the cystine knot growth factors. The holo-hormone consists of an a and b subunit. Within a species the a -subunit is identical with 92 amino acids, but the b-subunit varies according to which hormone it belongs. The b-subunit defines biological specificity. The holo-hormone is required for a productive interaction with its receptor. hCG is the only placental member of the Glycoprotein Hormone family, and is essential for the early maintainence of pregnancy.Monoclonal antibodies(mabs), MW ~150kDa, against hCG are used in; the early detection of pregnancy, design of antifertility vaccines, in the detection of certain cancers, and investigations of receptor binding. Fragment antibodies (Fab) have been prepared by papain digestion of whole antibody.
Crystals of hCG+FabB111 and hCG+A113 complexes show weak diffraction. FabB111 and FabINN-hCG-53 (Fab53) crystals have been grown.
Antibody B111 is directed against the C-terminal region of the b-subunit. Diffraction data has been collected to 2.8 Å for the FabB111 on the MAC Science 2020 Image Plate at room temperature. The structure has been solved by molecular replacement using AMoRe [1], and refinement is in progress.Antibody INN-hCG-53 is directed against c1/c2 epitope that involves residues from both subunits of the hormone. A crystal of Fab53 has shown diffraction to 2.8 Å at the synchrotron radiation source, Station 9.6, Daresbury, at room temperature.