“…Depending on the initial and subsequent substitutions on the GalNAc residue, a wide range of O-linked core structures is possible (25). Little, however, is known of the effects of local peptide sequence on O-glycan elongation (23,(32)(33)(34)(35)(36)(37), although a number of examples of site-specific elongation of N-linked glycans are known (30, 38 -46). Factors affecting site-specific N-glycan 1 The abbreviations used are: ppGalNAc transferase, UDP-GalNAc: polypeptide ␣-GalNAc transferase; ␣2-Fuc transferase, GDP-fucose: galactose -1,3-␣1,2-fucosyltransferase; core 1 3-Gal transferase, UDP-galactose:␣-N-acetylgalactosamine -1,3-galactosyltransferase; ST6GalNAc, GalNAc ␣2,6-sialyltransferase; Fuc, fucose; NeuNGl, N-glycoloylneuraminic acid or sialic acid; PSM, porcine submaxillary mucin; TR, tandem repeat; PTH, phenylthiohydantoin; Native GalNAc or (T)TTTR-PSM, Core 1 or (T)TROTR-PSM, Trisaccharide, or (T)TROGNTR-PSM, a series of differentially deglycosylated preparations of the PSM multiple tandem repeat domain described under "Materials and Methods" and under "Results," where (T) represents the 81-residue tandem repeat domain obtained after trypsinolysis; TFMSA, trifluoromethanesulfonic acid; SOG, glycosylated Ser; SOH, nonglycosylated Ser; TOG, glycosylated Thr; TOH, nonglycosylated Thr.…”