Expression of biologically active beta subunit of bovine follicle-stimulating hormone in the methylotrophic yeast Pichia pastoris.

Follicle-stimulating hormone (FSH), a pituitary gonadotropin, is a heterodimer composed of an alpha subunit, which is common to all the glycoprotein hormones, noncovalently associated with the hormone-specific beta subunit. The objective of the present study is to develop a recombinant DNA expression system for the beta subunit of FSH that can be applied to study structure-function relationships while producing large quantities of the hormone subunit for immuno-contraceptive, clinical, and veterinary purposes. We report here the expression of biologically active bovine FSH beta (bFSH beta) in the methylotrophic yeast Pichia pastoris. The Pichia-expressed FSH beta (pFSH beta) was secreted into the culture medium and was found to be immunologically very similar to pituitary-derived ovine FSH beta. Replacement of cognate signal peptide with the yeast alpha mating factor signal peptide increased the level of expression from 230 ng/ml (cognate signal peptide) to 4 micrograms/ml (alpha mating factor signal peptide) of the culture supernatant. pFSH beta His.tag (pFSH beta with six histidine residues at the C terminus) was purified to apparent homogeneity using one-step nickel affinity chromatography. The molecular weight of purified pFSH beta His.tag was approximately 22,000, which was slightly higher than that of the pituitary-derived ovine FSH beta. pFSH beta His.tag could assemble with the alpha subunit to yield a heterodimer capable of binding to the FSH receptors and also elicit biological response. These data show that pFSH beta His.tag is properly folded and biologically active.