Journal
PROTEINS-STRUCTURE FUNCTION AND BIOINFORMATICS
Volume 90, Issue 5, Pages 1210-1218Publisher
WILEY
DOI: 10.1002/prot.26303
Keywords
CA125; mucin; ovarian cancer; pancreatic cancer; unknown function
Categories
Funding
- National Cancer Institute of the National Institutes of Health [R15CA242349]
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MUC16 is a membrane bound glycoprotein involved in the progression and metastasis of pancreatic and ovarian cancer. The structure of its SEA domain was determined, revealing a canonical ferredoxin-like fold and a conserved disulfide bond. The study confirmed that the CA125 epitope, used for monitoring ovarian cancer treatment, is localized to the SEA domain. These findings provide insights into the functional role of MUC16 SEA domains and the antibody recognition of the CA125 epitope.
MUC16 is a membrane bound glycoprotein involved in the progression and metastasis of pancreatic and ovarian cancer. The protein is shed into the serum and the resulting cancer antigen 125 (CA125) can be detected by immunoassays. The CA125 epitope is used for monitoring ovarian cancer treatment progression, and has emerged as a potential target for antibody mediated immunotherapy. The extracellular tandem repeat domain of the protein is composed of repeating segments of heavily glycosylated sequence intermixed with homologous SEA (Sperm protein, Enterokinase and Agrin) domains. Here we report the purification and the first X-ray structure of a human MUC16 SEA domain. The structure was solved by molecular replacement using a Rosetta generated structure as a search model. The SEA domain reacted with three different MUC16 therapeutic antibodies, confirming that the CA125 epitope is localized to the SEA domain. The structure revealed a canonical ferredoxin-like fold, and contained a conserved disulfide bond. Analysis of the relative solvent accessibility of side chains within the SEA domain clarified the assignment of N-linked and O-linked glycosylation sites within the domain. A model of the glycosylated SEA domain revealed two major accessible faces, which likely represent the binding sites of CA125 specific antibodies. The results presented here will serve to accelerate future work to understand the functional role of MUC16 SEA domains and antibody recognition of the CA125 epitope.
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