Tumor Biology

, Volume 31, Issue 5, pp 495–502 | Cite as

Synthesis and structural characterization of the peptide epitope of the ovarian cancer biomarker CA125 (MUC16)

  • Zach T. Berman
  • Lee J. Moore
  • Kathleen E. Knudson
  • Rebecca J. Whelan
Research Article


A highly conserved region of 21 amino acids flanked by cysteine residues, contained within a larger repeated domain, has been proposed to be the antibody-binding site in the ovarian cancer biomarker CA125 (MUC16). In this study solid-phase peptide synthesis with Fmoc protection chemistry was used to assemble a 21-mer peptide corresponding to the most frequently occurring antibody binding sequence in CA125. Potentially significant sequence variants were also synthesized. Peptide secondary structure was investigated using Fourier transform infrared spectroscopy, revealing the consensus sequence peptide to be largely unstructured at physiological pH whether the cysteine residues were reduced or were oxidized to form an intramolecular disulfide bond. Substitution of serine for proline at position 8 (P8S) results in β-sheet formation in peptides involved in intramolecular disulfide bonds. This β-sheet structure does not persist in peptides incapable of intramolecular disulfide bonding because of sequence nor in peptides treated with the reducing agent dithiothreitol. In CA125, P8S is predicted to occur in ∼25% of repeat domains, suggesting that this structural motif is a non-negligible contributor to overall structure and function. These findings suggest that future structural characterization efforts of CA125 should be especially mindful of the amino acid sequence and oxidation state of the protein.


CA125 MUC16 Ovarian cancer Biomarker Synthetic peptide Repeat domain Epitope Infrared spectroscopy FTIR 



The authors thank Manish Mehta, Sean Decatur, and Kalani Seu for material and technical assistance. Funding was received from the Camille and Henry Dreyfus Foundation, the Oberlin-Michigan-Kalamazoo (OKUM) faculty exchange grant and Oberlin College.


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Copyright information

© International Society of Oncology and BioMarkers (ISOBM) 2010

Authors and Affiliations

  • Zach T. Berman
    • 1
  • Lee J. Moore
    • 1
  • Kathleen E. Knudson
    • 1
  • Rebecca J. Whelan
    • 1
  1. 1.Department of Chemistry and BiochemistryOberlin CollegeOberlinUSA

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