We previously demonstrated that an inactive point mutant of mucinase StcE, called StcEE447D, is an effective enrichment tool to probe the mucinome from complex samples including cancer cell lines, human serum, and crude ovarian cancer patient ascites fluid.61,22 Here, we performed a protein-level mucin enrichment on HeLa lysate with StcEE447D and digested the enriched mucins with SmE and PNGaseF (Figure 4A, orange). This evidence concerns the gene MUC5AC and cancer.