Mapping of assembled epitopic regions of human chorionic gonadotropin reveals proximity of CTPα to the determinant loop ß93-100.

Three overlapping assembled epitopes of ßhCG have been mapped using MAb probes and a single step solid phase radioimmunoassay. These epitopes have been shown to be at receptor binding region comprising of the loop region ß Cys93-Cys100. Importance of disulphide bonds in maintaining integrity of these epitopes is assessed. Two MAbs (INN 58 and INN 22) interact with the ß region as well as the α C-terminal peptide, while the other MAb INN 24 interacts with only the ß region. Cross-reactivity pattern with ßhCG and hLH as well as the reported crystal structure of hCG substantiates the epitope identification. The results demonstrate utility of MAbs as probes in investigations on three-dimensional structure of gonadotropins.