Mapping of an assembled epitope of human follicle-stimulating hormone-beta utilizing monoclonal antibodies, synthetic peptides, and hormone-receptor inhibition.
Monoclonal antibodies (mabs) to human (h) FSH were utilized to probe epitopes of the beta-subunit of hFSH (hFSH beta). These mabs had an average approximate affinity constant (Ka) of 10(8) M-1 for hFSH beta and 10(7) M-1 for heterodimeric hFSH. Hormone specificity of mabs for hFSH beta was demonstrated by a lack of cross-reactivity with hCG alpha, FSH alpha, or LH alpha. Epitope specificity of each mab was initially assessed by determining whether solid phase mab could bind to [125I]hFSH already bound to mabs in liquid phase. In addition, it was determined whether [125I]mab could bind to hFSH already bound to solid-phase mabs. Both epitope cross-matching protocols indicated that all mabs bound to the same epitopes on hFSH beta. Next, synthetic peptides corresponding to the sequence of hFSH beta were used in an enzyme-linked immunosorbent assay to map this epitope. All mabs bound to peptides 7-19, 1-20, 33-53 and 66-85 but did not bind or bound weakly to peptides 81-100, 95-103, and 103-110. Titration experiments were performed using different concentrations of peptide (0.3-41 nmol) and one mab 3G3 (500 ng-25 ng) in the enzyme-linked immunosorbent assay. The product of the lowest mass of both peptide and antibody which gave a positive result was used to rank the peptides for their binding with mab 3G3. Peptides were ranked in the following descending order of potency: 33-53, 49-67, 66-85 much greater than 16-36, 1-20, 95-103, 52-65, 81-100, and 103-110. Ability of the mabs to inhibit binding of [125I]hFSH to bovine testis membrane receptor (Rec) was also studied. When [125I]hFSH was preincubated with increments of each mab for 2 h at 25 C before adding Rec with further incubation for 16 h, all mabs inhibited [125I]hFSH binding to Rec. The data suggest that most of the hFSH beta molecule has a conformation enabling all antibody recognizable regions to be in close proximity to each other. The present study provides evidence for an assembled epitope comprising in part, amino acids 33-53, which has been previously shown to be involved in receptor binding. Peptide sequences 49-67 and 66-85 are neighboring sequences in this assembled epitope which contains the determinants for receptor binding.
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
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Vakharia
J A
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Dias
A N
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Thakur
T T
TT
Andersen
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A
O'Shea
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D000939:Epitopes / Q000032:analysis*; D005640:Follicle Stimulating Hormone / Q000138:chemical synthesis / Q000276:immunology*; D037201:Follicle Stimulating Hormone, beta Subunit; D006801:Humans; D007136:Immunoglobulins; D010455:Peptides / Q000138:chemical synthesis* / Q000276:immunology; D011487:Protein Conformation; D011863:Radioimmunoassay; D012984:Software
D000911:Antibodies, Monoclonal; D000939:Epitopes; D037201:Follicle Stimulating Hormone, beta Subunit; D007136:Immunoglobulins; D010455:Peptides; D005640:Follicle Stimulating Hormone