Studies on structure-function relationships of human choriogonadotropins with C-terminally shortened alpha-subunits....

Recombination products composed of the native beta-subunit and an alpha-subunit with an enzymatically shortened C-terminal region showed a diminished (less than 5 amino acids removed) or - in the case of des-(88-92)-alpha/native beta - a completely abolished ability to bind to testicular LH/hCG receptors of the rat. An antigenic determinant which is present in native hCG but not in the isolated subunits was not or incompletely expressed in the modified hormone species. Antigenic determinants which are characteristic for the isolated alpha-subunit, however, were not affected by removal of the C-terminal residues 88-92. The immunologic experiments indicate that hCG containing an alpha-subunit with a shortened C-terminal region differs from native hCG in its conformation. These conformational changes are probably responsible for the loss in receptor-binding ability.