A hybrid protein containing the toxic subunit of ricin and the cell-specific subunit of human chorionic gonadotropin. I. Synthesis and characterization.

In order to study the mechanisms involved in the interaction of cell-surface components and effector proteins, we synthesized a double-labeled dimeric hybrid molecule consisting of the toxic A subunit of the lectin ricin and the cell-specific beta subunit of human chorionic gonadotropin (hCGbeta). Utilizing methyl-5-bromovalerimidate, a disulfide cross-linked conjugate of hCGbeta and toxin subunit A was prepared in 30% yield relative to hCGbeta input. The dimeric protein, purified by gel filtration and ion exchange chromatography, was characterized by: (a) sodium dodecyl sulfate-containing polyacrylamide gel electrophoresis in the presence and absence of 2-mercaptoethanol, (b) analysis by gel filtration chromatography in the presence and absence of 2-mercaptoethanol, and (c) precipitation with antibodies specific for hCG and subunit A.