Glycosylation of natural human neutrophil gelatinase B and neutrophil gelatinase B-associated lipocalin

Gelatinase B is a matrix metalloproteinase (MMP-9) involved in tissue remodeling, development, cancer, and inflammation. Neutrophils produce three major forms of (pro)gelatinase B: 92 kDa monomers, homodimers, and complexes of gelatinase B covalently bound to neutrophil gelatinase B-associated lipocalin (NGAL). In contrast to the case for other proteinases, little information about the glycosylation of any natural human MMP is available. Here, both gelatinase B and NGAL were purified from human peripheral blood neutrophils, and the entire contents of the released N- and O-glycan pools were analyzed simultaneously using recently developed high-performance liquid chromatography-based technology. The results are discussed within the context of the domain structure of gelatinase B and a molecular model of NGAL based on data from this study and the three-dimensional nuclear magnetic resonance (NMR) structure of the protein. More than 95% of the N-linked glycans attached to both gelatinase B and NGAL were partially sialylated, core- fucosylated biantennary structures with and without outer arm fucose. The O- linked glycans, which were estimated to comprise approximately 85% of the total sugars on gelatinase B, mainly consisted of type 2 cores with Galβ1,4GlcNAc (lactosamine) extensions, with or without sialic acid or outer arm fucose. This paper also contains the first report of O-linked glycans attached to NGAL. Although both proteins were isolated from neutrophils and contained O-linked glycans mainly with type 2 cores, the glycans attached to individual serine/threonine residue(s) in NGAL were significantly smaller than those on gelatinase B. In contrast to NGAL, gelatinase B contains a region rich in Ser, Thr, and Pro typical of O-glycosylated mucin-like domains.