Synthetic hFSH peptide constructs in the evaluation of previous studies on the hFSH receptor interaction

The human follicle-stimulating hormone (hFSH) belongs to a family of glycoprotein hormones which contains two non-identical subunits. This paper describes the design and synthesis of a series of synthetic hFSH constructs as putative ligands for the receptor. The design of these constructs is based on the crystal structure of hCG and molecular modelling using the program package Insight II/Discover. The designed constructs contain peptides ranging from 7 to 48 amino acid residues, disulphide bridges and glycan residues. All the synthetic peptides were synthesized by the stepwise solid-phase method using Fmoc chemistry. Two of the synthetic peptides contain the glycosylated amino acid. Asn(GlcNAc-GlcNAc) and both were prepared using fully protected glycosylated building blocks in the solid-phase peptide synthesis. The disulphide bridges were formed from acetamidomethyl-protected glycopeptides and peptides by a direct deprotection/oxidation method using thallium(III) trifluoroacetate. Mass spectroscopy and amino acid analysis were used for characterization of the synthetic hFSH glycopeptides and peptides. The synthetic hFSH constructs were tested for binding activity on FSH receptor assays but none showed improved binding properties compared with the naturally occurring hormone. It was finally demonstrated that non-related peptides showed non-specific binding at the same level as reported for specific peptides.