THE PRESENCE OF A HUMAN CHORIONIC GONADOTROPIN-LIKE PROTEIN AND ITS BINDING-SITE IN SACCHAROMYCES-CEREVISIAE

In this study, we characterize from Saccharomyces cerevisiae: 1) a pro tein that has immunological similarities to human chorionic gonadotrop in (hCG), and 2) a binding site for this hCG-like protein which also b inds hCG and human luteinizing hormone (hLH). Saccharomyces cerevisiae chorionic gonadotropin-like protein (ScCGLP) was purified in several steps. This protein when analyzed by SDS-PAGE, under nondenaturing con ditions, produced two bands, one at 110-kDa, and another at 57.5-kDa. Under denaturing conditions, only the 57.5-kDa band appeared, This 57. 5-kDa band also reacted in a western blot, using a polyclonal antibody directed against hCG. Purified ScCGLP reacted in the following hCG im munoassays: 1) polyclonal rabbit anti-hCG equilibrium assay, 2) carbox yl-tail hCG equilibrium assay, 3) two equilibrium assays using monoclo nal antibodies, and 4) free alpha-chain subunit equilibrium assay usin g a monoclonal antibody. Characterization of hCG/hLH binding sites in Saccharomyces cerevisiae was performed, and the ability of the ScCGLP to displace I-125-hCG was also shown. Human CG and hLH were able to co mpete for I-125-hCG binding to Saccharomyces cerevisiae blastospores ( Kds of approximately 10(-8) M), while ScCGLP competed with higher affi nity (Kd 9.41 x 10(-10) M). The hCG-like immunoactivity was also prese nt in saccharomyces growth media, as well as in all brands of commerci al beer studied.