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A Mucin-Specific Protease Enables Molecular and Functional Analysis of Human Cancer-Associated Mucins

preprint
submitted on 12.11.2018 and posted on 13.11.2018 by Stacy Malaker, Kayvon Pedram, Michael J. Ferracane, Elliot C. Woods, Jessica Kramer, Oliver Dorigo, Carolyn Bertozzi

Mucins are a class of highly O-glycosylated proteins that are ubiquitously expressed on cellular surfaces and are important for human health, especially in the context of carcinomas. However, the molecular mechanisms by which aberrant mucin structures lead to tumor progression and immune evasion have been slow to come to light, in part because methods for selective mucin degradation are lacking. Here we employ high resolution mass spectrometry, polymer synthesis, and computational peptide docking to demonstrate that a bacterial protease, called StcE, cleaves mucin domains by recognizing a discrete peptide-, glycan-, and secondary structure- based motif. We exploited StcE’s unique properties to map glycosylation sites and structures of purified and recombinant human mucins by mass spectrometry. As well, we found that StcE will digest cancer-associated mucins from cultured cells and from ovarian cancer patient-derived ascites fluid. Finally, using StcE we discovered that Siglec-7, a glyco-immune checkpoint receptor, specifically binds sialomucins as biological ligands, whereas the related Siglec-9 receptor does not. Mucin-specific proteolysis, as exemplified by StcE, is therefore a powerful tool for the study of glycoprotein structure and function and for deorphanizing mucin-binding receptors.

Funding

Chemical Cell Surface Engineering

National Institute of General Medical Sciences

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History

Email Address of Submitting Author

bertozzi@stanford.edu

Institution

Stanford University

Country

USA

ORCID For Submitting Author

0000-0003-4482-2754

Declaration of Conflict of Interest

The authors declare no competing financial interests.

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