Cystic fibrosis and bacterial colonization define the sputum N-glycosylation phenotype

Abstract

Although mucin O-glycosylation of sputum from individuals suffering from cystic fibrosis (CF) is known to be altered relative to their unaffected counterparts, protein N-glycosylation of CF sputum remains structurally and functionally under-characterized. We report the first N-glycome of soluble proteins in sputum derived from five CF patients, two pathogen-free and two pathogen-infected/colonized non-CF individuals suffering from other pulmonary conditions. N-Glycans were profiled using porous graphitized carbon-liquid chromatography-negative ion-tandem mass spectrometry following enzymatic release from sputum proteins. The composition, topology and linkage isomers of 68 N-glycans were characterized and relatively quantified. Recurring structural features in all sputum N-glycomes were terminal α2,6-sialylation, α1,6-core fucosylation, β1,4-bisecting GlcNAcylation and compositions indicating paucimannosylation. Despite covering different genotypes, age, gender and microbial flora, the sputum N-glycomes showed little interpatient and longitudinal variation within CF patients. Comparative N-glycome analysis between inter-patient group revealed that lung infection/colonization, in general, extensively enriches the CF sputum N-glycosylation phenotype with paucimannose with simultaneous over-sialylation/fucosylation and under-bisecting GlcNAcylation of complex/hybrid N-glycans. In contrast, the sputum from CF patients had only slightly increased abundance of paucimannose N-glycans relative to pathogen-infected/colonized non-CF individuals. Similar to mucin O-glycosylation, protein N-glycosylation appears to be regulated primarily as a secondary effect of bacterial infection and inflammation rather than the CF pathogenesis in sputum. This study provides new structural N-glycan information to help understand the complex cellular and molecular environment of the CF affected respiratory tract.

Keywords: N-glycans; bacterial colonization; cystic fibrosis; paucimannose; sputum.