ABSTRACT: An in vitro prepared NTSR1-Arr2 complex was stabilized by use of heterobifunctional crosslinker. Here we characterize the crosslinks observed upon photo-illumination of this complex.
Project description:After gaining access to the endo-lysosomal pathway, several viruses depend on lysosomal cathepsin proteases to cleave their structural proteins triggering productive entry. Targeting of cathepsins and other luminal lysosomal proteins to lysosomes requires their modification with mannose 6-phosphate (M6P) signals. Key to M6P tagging is N-acetylglucosamine (GlcNAc)-1-phosphotransferase whose deficiency leads to the severe lysosomal storage disorder mucolipidosis II (MLII). Here, using genome-scale CRISPR screens, we identify the transmembrane protein TMEM251 as critically important for viral infection by cathepsin-dependent viruses including reovirus, Ebola virus, and SARS-CoV-2. We demonstrate that Golgi-resident TMEM251 is essential for lysosomal sorting and activity of cathepsins. Mechanistically, we show that TMEM251 deficiency in human cells results in global loss of M6P on luminal lysosomal proteins by destabilizing GlcNAc-1-phosphotransferase. Tmem251 knockout mice reveal characteristics typical of MLII including hypersecretion of lysosomal enzymes and accumulation of lysosomal storage material in isolated fibroblasts. Finally, we demonstrate that human pathogenic TMEM251 alleles fail to rescue lysosomal sorting defects in knockout cells. Our results uncover a crucial role of TMEM251 in M6P-dependent lysosomal transport and viral infection. Overall, work here reveals the biochemical basis of an inherited MLII-like disease caused by mutations in TMEM251 and provides insights into infection mechanisms of a broad class of medically important viruses.
Project description:Non-alcoholic fatty liver disease (NAFLD), recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD to date. Despite its discovery twenty years ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.
Project description:We performed a large-scale, intact glycopeptide-based glycoproteomics study of human brain tissue samples from neuropathologically confirmed AD cases and their age-matched controls. The study provided a system-level view of human brain protein glycoforms and site-specific glycan modifications. Our analyses revealed previously unknown changes in protein glycoforms and site-specific glycans in AD brain. Our findings provide novel insights into the roles of glycan modifications in brain dysfunction in AD.
Project description:In this study, we explored the use of BONCAT in Synechococcus sp. – a globally important cyanobacteria. We characterized the growth and microscopically quantified HPG uptake under a range of HPG concentrations in marine Synechococcus sp. Further, we examined changes in protein expression of Synechococcus sp. grown under normal and nitrate-stressed conditions relative to a non-HPG control.
Project description:Protein glycosylation is a critical PTM for the stability and biological function of many proteins, but full characterisation of site-specific glycosylation of proteins remains analytically challenging. Collision induced dissociation (CID) is the most common fragmentation method used in LC-MS/MS workflows, but loss of labile modifications render CID inappropriate for detailed characterisation of site-specific glycosylation. Electron-based dissociation (ExD) methods provide alternatives that retain intact glycopeptide fragments for unambiguous site localisation, but these methods often underperform CID due to increased reaction times and reduced efficiency. Electron activated dissociation (EAD) is another strategy for glycopeptide fragmentation. Here, we use a ZenoTOF 7600 SCIEX instrument to compare the performance of various fragmentation techniques for the analysis of a complex mixture of mammalian O- and N-glycopeptides.
Project description:The envelope glycoprotein GP of the ebolaviruses is essential for host cell attachment and entry. It is also the primary target of the protective and neutralizing antibody response in both natural infection and vaccination. GP is heavily glycosylated with up to 17 predicted N-linked sites, numerous O-linked glycans in its disordered mucin-like domain (MLD), and three predicted C-linked mannosylation sites. Glycosylation of GP is important for host cell attachment to cell-surface lectins, as well as GP stability and fusion activity. Moreover, it has been shown to shield GP from neutralizing activity of serum antibodies. Here, we use mass spectrometry-based glycoproteomics to profile the site-specific glycosylation patterns of ebolavirus GP, including N-, O-, and C-linked glycans.
Project description:Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell disorder, leading to the presence of monoclonal antibody (i.e., M-protein) in serum, without clinical symptoms. Here we present a case study in which we detect MGUS by liquid-chromatography coupled with mass spectrometry (LC-MS) profiling of IgG1 in human serum. We detected a Fab-glycosylated M-protein and determined the full heavy and light chain sequences by bottom-up proteomics techniques using multiple proteases, further validated by top-down LC-MS. Moreover, the composition and location of the Fab-glycan could be determined in CDR1 of the heavy chain.
Project description:In this study, we used quantitative proteomics mass spectrometry with 16-plex TMT labeling to compare individual protein levels of DMSO and 1 μM CSN5i-3-treated K562 cells for 2, 8, and 24 hours. CSN5i-3 is a selective and potent inhibitor of Cop9 Signalosome (CSN), which regulates the activity of Cullin-RING E3 ubiquitin ligases (CRLs). CSN5i-3 treatment resulted in reduced CSN activity, and consequently increased cullin neddylation and constitutively active CRL. Gene Ontology analysis of the changed proteins between DMSO- and CSN5i-3-treated samples showed the enrichment of CSN subunits, cell cycle and chromosome-related components, and phosphatase complex, which include multiple CSN subunits (e.g., CSN7B and CSN5), components of CRLs, especially CRL SRs (e.g., SKP2, ELOA and DCAF1/VPRBP), and known substrates of CRLs (e.g., MAGEA6, GLUL, and RHOB). Indeed, eight out of the top 20 most decreased proteins were CRL adaptor and substrate receptors, two out of the top 20 were E2 proteins (CDC34/UBE2R1 and UBE2R2), and two were CSN subunits. Eight out of the top 20 most increased proteins were reported CRL substrates.
Project description:Corticosteroid-binding globulin (CBG) is a serum glycoprotein that binds and delivers anti-inflammatory cortisol to inflammatory sites through neutrophil elastase (NE)-mediated proteolysis of an exposed reactive centre loop (RCL) on CBG. Timely and tissue-specific delivery of cortisol is critical to alleviate inflammation including in life-threatening septic shock conditions. Important for the cortisol delivery mechanism, which is facilitated by proteolytic cleavage of RCL of CBG and conformational changes to the protein, we recently identified novel O-glycosylation events within the RCL and documented their inhibition of RCL proteolysis (Chernykh et al., 2023). While these observations are of significance as they implicate RCL O-glycosylation as a potential regulator of cortisol delivery, the link to septic shock remains unexplored. To this end, we used mass spectrometry to profile the RCL O-glycosylation of CBG purified from serum of twelve septic shock patients. Serum CBG from all patients exhibited RCL O-glycosylation comprising both sialyl T and/or disialyl T (NeuAc1-2Gal1GalNAc1) O-glycan structures decorating exclusively the Thr342 site. Importantly, relative to less severe cases, individuals presenting with the most severe illness displayed elevated RCL O-glycosylation upon ICU admission, suggesting a previously unknown link to septic shock severity. Overall, we have elucidated RCL O-glycosylation events of serum CBG, which improve our understanding of molecular mechanisms governing the timely and tissue-specific delivery of cortisol to inflammatory sites. The work provides clues to molecular aberrations and disease mechanisms underpinning septic shock.
Project description:Site-specific glycosylation analysis by nLC-MS/MS of recombinant human FCγ receptor I, III V158 and III 158F, and mouse FCγ receptor I, III and IV.