A synthetic oligopeptide derived from human thyrotropin receptor sequence binds to Graves' immunoglobulin and inhibits thyroid stimulating antibody activity but lacks interactions with TSH.

An 11-residue oligopeptide, P-195, was synthesized to match human thyrotropin (TSH) receptor structure from No. 333 to 343 of amino acid sequence. Preincubation of 5 Graves' IgGs with P-195 up to 10 micrograms resulted in dose-dependent reductions of thyroid stimulating antibody (TSAb) activity. [125I] labeled P-195 was found to bind Graves' IgG. The bound radioactivity correlated significantly with their TSAb activity (N = 25, r = 0.587, p less than 0.01). A peptide having a completely reverse sequence as P-195 did not show such biological activity. The peptide did not affect TSH and thyrotropin binding inhibitor immunoglobulin (TBII) on their receptor binding nor biological activities. P-195 was concluded to have a part of TSAb binding sites.