Glycomic mapping of O- and N-linked glycans from major rat sublingual mucin

Carbohydrate moieties of salivary mucins play various roles in life processes, especially as a microbial trapping agent. While structural details of the salivary O-glycans from several mammalian sources are well studied, very little information is currently available for the corresponding N-glycans. The existence of N-glycans alongside O-glycans on mucin isolated from rat sublingual gland has previously been implicated by total glycosyl compositional analysis but the respective structural data are both lacking. The advent of facile glycomic mapping and sequencing methods by mass spectrometry (MS) has enabled a structural reinvestigation into many previously unsolved issues. For the first time, high energy collision induced dissociation (CID) MALDI-MS/MS as implemented on a TOF/TOF instrument was applied to permethyl derivatives of mucin type O-glycans and N-glycans, from which the linkage specific fragmentation pattern could be established. The predominant O-glycans carried on the rat sublingual mucin were defined as sialylated core 3 and 4 types whereas the N-glycans were determined to be non-bisected hybrid types similarly carrying a sialylated type II chain. The masking effect of terminal sialylation on the tight binding of rat sublingual mucin to Galβ1→4GlcNAc specific lectins and three oligomannose specific lectins were clearly demonstrated in this study.