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Position-specific N- and O-glycosylation of the reactive centre loop impacts neutrophil elastase-mediated proteolysis of corticosteroid-binding globulin

ABSTRACT: Corticosteroid-binding globulin (CBG) delivers anti-inflammatory cortisol to inflamed tissues through the proteolytic cleavage of an exposed reactive centre loop (RCL) by neutrophil elastase (NE). We previously demonstrated that RCL-localised Asn347-linked N-glycans impact NE proteolysis, but a comprehensive structure-function characterisation of the RCL glycosylation is still required to better understand CBG glycobiology. Herein, we firstly performed RCL-centric glycoprofiling of serum-derived CBG to elucidate the Asn347-glycans and then used molecular dynamics (MD) simulations to study their impact on NE proteolysis. Importantly, we also identified novel O-glycosylation (di/sialyl T) across four RCL sites (Thr338/Thr342/Thr345/Ser350) of serum CBG close to the NE-targeted Val344-Thr345 cleavage site. A restricted N- and O-glycan co-occurrence pattern on the RCL involving exclusively Asn347 and Thr338 sites was experimentally observed and supported in silico by modelling of a CBG-GalNAc-transferase (GalNAc-T) complex with various RCL glycans. GalNAc-T2 and -T3 abundantly expressed by liver and gallbladder, respectively, showed in vitro a capacity to transfer GalNAc (Tn) to multiple RCL sites suggesting their involvement in RCL O-glycosylation. Recombinant CBG (rCBG) was then used to determine roles of RCL O-glycosylation through longitudinal NE-centric proteolysis experiments, which demonstrated that both sialo- (disialyl T) and asialo-glycans (T) decorating Thr345 inhibit NE proteolysis. Synthetic RCL O-glycopeptides expanded on these findings by showing that Thr345-Tn and Thr342-Tn confer strong and moderate protection against NE cleavage, respectively. MD substantiated that short Thr345-linked O-glycans abrogate NE interactions. In conclusion, we report on strategically-positioned and biologically-relevant CBG RCL glycans, which improve our understanding of mechanisms governing cortisol delivery to inflamed tissues.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Blood Serum

SUBMITTER: Anastasia Chernykh

LAB HEAD: Morten Thaysen-Andersen

PROVIDER: PXD046405 | Pride | 2023-12-05

REPOSITORIES: Pride

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Project description:Proteolytic processing is an irreversible post-translational modification functioning as a ubiquitous regulator of cellular activity. Protease activity is tightly regulated by control of gene expression, compartmentalisation of enzyme and substrate, zymogen activation, enzyme inactivation, and substrate availability. Emerging evidence suggests that proteolysis can also be regulated by substrate glycosylation and that glycosylation of individual sites on a substrate can decrease, or in rare cases, increase its sensitivity to proteolysis. In the present study we investigated the relationship between site-specific O-glycosylation and proteolytic cleavage of extracellular proteins. By in silico analysis we found a significant association between O-glycosylation sites and cleavage sites. We then used a positional proteomic strategy, Terminal Amine Isotopic Labelling of Substrates (TAILS) to map in vivo cleavage sites in HepG2 cells with and without one of the key initiating GalNAc-transferases, GalNAc-T2. To reduce complexity, the comparison were performed in so-called SimpleCells. In these cells the Core 1 β3-galactosyltransferase-specific molecular chaperone (COSMC; C1GALT1C1) has been knocked out, resulting in global truncation of O-glycans leaving only the initial GalNAc. Surprisingly, we found that loss of GalNAc-T2 resulted in not only an increase in cleavage, but also a decrease in cleavage across a broad range of other substrates, including key regulators of the protease network. GALNT2 has previously been identified as a candidate gene for dyslipidaemia and has been shown to specifically glycosylate central regulators of lipid homeostasis, here we find altered processing of several of these regulators including Apolipoproteins B (ApoB) and the Phospholipid transfer protein (PLTP), providing new clues to the link between GALNT2 and lipid homeostasis. In contrast to the findings from the majority of previous studies, these results indicate that O-glycosylation can both decrease and increase substrate cleavage. We challenged this system with exogenous matrix metalloproteinase 9 (MMP9) and neutrophil elastase and observed substantial changes to the neutrophil elastase N-terminome, but no evidence for a similar role for MMP9. Overall, we show that loss of O-glycosylation leads to a general decrease in cleavage, that GalNAc-T2 O-glycosylation affects key regulators of the cellular proteolytic network, including multiple members of the Serpin family.

Project description:Glycobiology plays a central role in prostate cancer (PCa), as evidenced by the aberrant glycosylation in PCa-derived glycoproteins. Understanding the protein glycosylation changes underling PCa onset and progression may open opportunities for the discovery of novel biomarkers for PCa detection and stratification as well as targets for PCa metastasis. Advances in mass spectrometry-based glycomics and glycoproteomics have opened up exciting avenues for deep characterisation of the immensely, yet poorly understood complex glycoproteome. In this study, we have used integrated glycomics and glycoproteomics to explore the protein, cell and tumour-grade specific N- and O- glycosylation signatures in surgically-removed fresh PCa tissues grouped into five PCa disease grades and tissues from benign prostatic hyperplasia patients (BPH). Porous graphitised carbon–liquid chromatography (PGC–LC)-MS/MS analysis was used to profile the N-and O-glycome, revealing PCa grade specific N and O glycosylation changes, including oligomannosidic and paucimannosidic, bisecting-GlcNAc and highly branched tri- and tetra-antennary fucosylated and sialylated N-glycans as well as sialylated core 1 and 2 type O-glycans. High resolution LC-MS/MS was then employed to capture the micro and macroheterogeneity of 1,085 N-glycosites (>7,400 unique N-glycopeptides) from 540 N-glycoproteins and 360 O-glycosites (>500 unique O-glycopeptides) from 178 O-glycoproteins and reveal protein and cell specific N- and O- glycosylation changes associated with PCa progression. We also showed PCa grade-specific increase in the expression of oligosaccharyltransferase (OST) subunits that correlate with changes in the site occupancy of N-glycoproteins. In conclusion, this study shows that integrated glycomics and glycoproteomics can provide unprecedented insight into key molecular features and site-specific glycan heterogeneity contributing to the highly diverse tumour-microenvironment and allow us to deconstruct the regulation of the protein, cell and tumour-grade-specific glycosylation associated with PCa onset and development.

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Position-specific N- and O-glycosylation of the reactive centre loop impacts neutrophil elastase-mediated proteolysis of corticosteroid-binding globulin

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