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 protein that has immunological similarities to human chorionic gonadotropin (hCG), and 2) a binding site for this hCG-like protein which also binds 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 conditions, 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 immunoassays: 1) polyclonal rabbit anti-hCG equilibrium assay, 2) carboxyl-tail hCG equilibrium assay, 3) two equilibrium assays using monoclonal antibodies, and 4) free alpha-chain subunit equilibrium assay using a monoclonal antibody. Characterization of hCG/hLH binding sites in Saccharomyces cerevisiae was performed, and the ability of the ScCGLP to displace I125-hCG was also shown. Human CG and hLH were able to compete for I125-hCG binding to Saccharomyces cerevisiae blastospores (Kds of approximately 10(-8) M), while ScCGLP competed with higher affinity (Kd = 9.41 x 10(-10) M). The hCG-like immunoactivity was also present in Saccharomyces growth media, as well as in all brands of commercial beer studied.
Caticha
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O
Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City.
Grover
S
S
Yu
W
W
Odell
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WD
D001665:Binding Sites; D001667:Binding, Competitive; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D006063:Chorionic Gonadotropin / Q000302:isolation & purification* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000302:isolation & purification* / Q000378:metabolism; D007457:Iodine Radioisotopes; D011863:Radioimmunoassay; D012441:Saccharomyces cerevisiae / Q000737:chemistry*
D002352:Carrier Proteins; D006063:Chorionic Gonadotropin; D005656:Fungal Proteins; D007457:Iodine Radioisotopes