The beta subunits of glycoprotein hormones. Formation of three-dimensional structure during cell-free biosynthesis of lutropin-beta.

Abstract

The folding of the hormone-specific (beta) subunit of the glycoprotein hormone bovine lutropin was studied after the translation and processing of bovine pituitary mRNA in a system derived from Krebs ascites tumor cells. Of the three forms of beta subunit recognized in this system, only the subunit which had both its prepeptide removed and an oligosaccharide moiety attached formed a tertiary structure which could be immunoprecipitated by an antiserum specific to isolated (folded) lutropin-beta. This glycosylated subunit also combined with added alpha subunit to form the dimeric alpha-beta complex. The results of the translation and processing experiments parallel those of previous experiments in which alpha subunit folding was examined. In contrast to alpha subunit, however, the difficulty of demonstrating correct refolding of beta subunit after reduction and reoxidation of its disulfide bonds strongly suggests that the formation of its correct tertiary structure not only requires carbohydrate attached to the peptide chain but also must occur during formation of the nascent beta chain.