Deglycosylation of a bifunctional lutropin-follitropin agonist reduced its follitropin activity more than its lutropin activity.
OBJECTIVE: To design a drug that blocks the gonadal actions of lutropins and follitropins.
DESIGN: Controlled in vitro study.
SETTING: Academic laboratory.
PATIENT(S): None.
INTERVENTION(S): We removed three glycosylation signals from an hCG-hFSH chimera known to have high affinity for LH and FSH receptors, expecting this would create a bifunctional antagonist (dgCFC). To offset the inhibition of subunit combination caused by deglycosylation of alpha-subunit loop 2, we prepared dgCFC as a single-chain fusion protein containing the alpha-subunit downstream of the chimeric beta-subunit.
MAIN OUTCOME MEASURE(S): Receptor binding, cyclic adenosine monophosphate accumulation.
RESULT(S): dgCFC bound LH or FSH receptors similar to hCG or hFSH. It was a partial agonist and had one tenth the efficacy of hFSH and two thirds the efficacy of hCG.
CONCLUSION(S): The surprising high residual lutropin activity of dgCFC indicated that its FSH residues offset the effects of deglycosylation, suggesting this approach to preparing a bifunctional antagonist is unlikely to lead to a useful drug. The increased lutropin efficacy of dgCFC relative to deglycosylated hCG supports the idea that oligosaccharides modulate glycoprotein hormone efficacy through an influence on hormone conformation.