Poster Presentation 24th Annual Lorne Proteomics Symposium 2019

Accessing the mannose-6-phosphate glycoproteome using titanium dioxide (TiO2) enrichment (#105)

Sayantani Chatterjee 1 , Rebeca K. Sakuma 1 2 , Morten Thaysen-Andersen 1
  1. Department of Molecular Sciences, Macquarie University, Sydney, NSW, Australia
  2. Department of Parasitology, Institute of Biomedical Sciences, University of Sau Paulo, Sau Paulo, Brazil

Lysosomal hydrolases receive mannose-6-phosphate (M6P) modifications while trafficking the ER-Golgi pathway, an N-glycosylation tagging process that directs enzymes to their lysosomal destination. Previously unknown extracellular roles of M6P-glycoproteins were recently suggested including the involvement in cell-to-cell communication and cell growth in inflammation and cancer. However, solid structural data is unavailable to determine the cellular expression of the “M6P-glycoproteome” and therefore the extracellular role of M6P-glycoproteins. Comprehensive characterisation of the M6P-glycoproteome is challenging owing to their low abundance and anionic character, which, in concert, limit their MS-detection using conventional analytical strategies. We have developed a novel method that enables isolation and thereby enhanced detection of both free reduced N-glycans and N-glycopeptides utilising titanium dioxide (TiO2)-SPE based enrichment followed by LC-MS/MS detection. Optimisation of the mobile phases (loading and elution conditions) was performed using isolated M6P-glycoproteins (myeloperoxidase and SMPDL3A). Firstly, it was demonstrated that M6P-glycans and glycopeptides quantitatively survive the short exposure to the acidic and alkaline conditions of the mobile phases. Efficient depletion of neutral and, surprisingly, sialylated glycans and glycopeptides were shown demonstrating preferential affinity of the M6P-glycoconjugates to TiO2 under the optimised loading condition. Phosphopeptides were efficiently depleted from the peptide samples using HILIC-SPE prior to the TiO2 enrichment to avoid analyte interference. Finally, the enrichment method was tested on a complex biological protein mixture derived from prostate cancer tissues and different neutrophil granules. Identification of a spectrum of M6P-glycans (Phos1-2Man3-8GlcNAc2) and M6P-glycopeptides (containing Phos1-2Man3-8GlcNAc2) originating from lysosome-like glycoproteins e.g. myeloperoxidase, cathepsin G, neutrophil elastase from neutrophil granules and extracellular glycoproteins including fibronectin, collagen and prostatic acid phosphatases from prostate cancer tissues demonstrated the potential of this enrichment method when applied to complex biological samples. In conclusion, this novel enrichment method offers parallel characterisation of M6P-glycans and M6P-glycopeptides enabling deep characterisation of the M6P-glycoproteome in a biologically relevant context.