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Glycomic mapping of pseudomucinous human ovarian cyst glycoproteins: Identification of Lewis and sialyl Lewis glycotopes

Expression of sialyl Lewis x (sLex) and sialyl Lewis a (sLea) on cell‐surface glycoproteins endows cells with the ability to adhere to E‐, P‐, and L‐selectins present on endothelia, platelets, or leukocytes. Special arrangements of these glycotopes in cancers are thought to play a key role in metastasis. Previous studies have mostly described membrane‐bound sLex and sLea activities. In this report, the major O‐glycans of the secreted human ovarian cyst sialoglycoproteins from a Le(a+) nonsecretor individual (human ovarian cyst sample 350) were characterized by MS/MS analyses and immuno‐/lectin‐chemical assays. The results showed that HOC 350 carries a large number of epitopes for sLex, sLea, and Lea reactive antibodies. Advanced MS/MS sequencing coupled with mild periodate oxidation and exoglycosidase digestions further revealed that the O‐glycans from HOC 350 are mostly of core 1 and 2 structures, extended and branched on the 3‐arm with both type I and type II chains, complete with variable degrees of terminal sialylation and/or fucosylation to yield the sLex or sLea epitopes. Thus, the underlying core and peripheral backbone structures are similar to that of a previously proposed composite structural model for nonsialylated human ovarian cysts O‐glycans, but with some notable distinguishing structural features in addition to sialylation.