Project description:The protein quality control sensors UDP-glucose: glycoprotein glucosyltransferase (UGGT) 1 and 2 are proposed to act as gatekeepers of the early secretory pathway. They initiate rebinding to the carbohydrate-dependent chaperones calnexin and calreticulin that associate with proteins possessing monoglucosylated glycans. The UGGTs control glycoprotein exit from the endoplasmic reticulum (ER) for trafficking to the Golgi or ER retention to provide additional folding opportunities. A quantitative glycoproteomics strategy was used to identify cellular glycoproteins modified by the UGGTs at endogenous levels and delineate the specificities of UGGT1 and UGGT2. UGGT substrates were comprised of seventy-one mainly large multidomain and heavily glycosylated proteins when compared to the general N-glycome. UGGT1 was the dominant glucosyltransferase with a preference towards large plasma membrane proteins whereas UGGT2 favored the modification of smaller, soluble lysosomal proteins. This study provides insight into the cellular secretory load that utilizes multiple rounds of carbohydrate-dependent chaperone intervention for proper maturation.
Project description:Although the composition of donkey milk is similar to that of human milk, systematic comparisons of the site-specific N-glycosylation patterns of their whey proteins are lacking. In this study, hydrophilic interaction chromatography-based enrichment of intact N-glycopeptides, coupled with a site-specific glycoproteomics strategy, was used to systematically characterise whey N-glycoproteins in donkey colostrum (DC), donkey mature milk (DM), human colostrum (HC), and human mature milk (HM) for the first time. We identified 628, 347, 868, and 425 site-specific N-glycans mapped to 135, 67, 113, and 60 glycoproteins in DC, DM, HC, and HM, respectively. Bioinformatic analysis revealed the potential biological effects of N-glycosylation modifications on the whey proteins themselves. Our findings elucidated the composition of donkey and human milk whey N-glycoproteins and their potential structure-activity relationships and provided guidance for the production of specific functional donkey milk products and the development of donkey milk-based infant formulas.
Project description:Protein glycosylation is a highly important, yet a poorly understood protein post-translational modification. Thousands of possible glycan structures and compositions create potential for tremendous site heterogeneity and analytical challenge. A lack of suitable analytical methods for large-scale analyses of intact glycopeptides has ultimately limited our abilities to both address the degree of heterogeneity across the glycoproteome and to understand how it contributes biologically to complex systems. Here we show that N-glycoproteome site-specific microheterogeneity can be captured at a global level via glycopeptide profiling with activated ion electron transfer dissociation (AI-ETD), enabling characterization of nearly 2,100 N-glycosites (> 7,500 unique N-glycopeptides) from mouse brain tissue. Moreover, we have used this unprecedented scale of glycoproteomic data to develop several new visualizations that will prove useful for analyzing intact glycopeptides in future studies. Our data reveal that N-glycosylation profiles can differ between subcellular regions and structural domains and that N-glycosite heterogeneity manifests in several different forms, including dramatic differences in glycosites on the same protein.