Dataset Information

Metabolism of vertebrate amino sugars with N-glycolyl groups: elucidating the intracellular fate of the non-human sialic acid N-glycolylneuraminic acid.

ABSTRACT: The two major mammalian sialic acids are N-acetylneuraminic acid and N-glycolylneuraminic acid (Neu5Gc). The only known biosynthetic pathway generating Neu5Gc is the conversion of CMP-N-acetylneuraminic acid into CMP-Neu5Gc, which is catalyzed by the CMP-Neu5Ac hydroxylase enzyme. Given the irreversible nature of this reaction, there must be pathways for elimination or degradation of Neu5Gc, which would allow animal cells to adjust Neu5Gc levels to their needs. Although humans are incapable of synthesizing Neu5Gc due to an inactivated CMAH gene, exogenous Neu5Gc from dietary sources can be metabolically incorporated into tissues in the face of an anti-Neu5Gc antibody response. However, the metabolic turnover of Neu5Gc, which apparently prevents human cells from continued accumulation of this immunoreactive sialic acid, has not yet been elucidated. In this study, we show that pre-loaded Neu5Gc is eliminated from human cells over time, and we propose a conceivable Neu5Gc-degrading pathway based on the well studied metabolism of N-acetylhexosamines. We demonstrate that murine tissue cytosolic extracts harbor the enzymatic machinery to sequentially convert Neu5Gc into N-glycolylmannosamine, N-glycolylglucosamine, and N-glycolylglucosamine 6-phosphate, whereupon irreversible de-N-glycolylation of the latter results in the ubiquitous metabolites glycolate and glucosamine 6-phosphate. We substantiate this finding by demonstrating activity of recombinant human enzymes in vitro and by studying the fate of radiolabeled pathway intermediates in cultured human cells, suggesting that this pathway likely occurs in vivo. Finally, we demonstrate that the proposed degradative pathway is partially reversible, showing that N-glycolylmannosamine and N-glycolylglucosamine (but not glycolate) can serve as precursors for biosynthesis of endogenous Neu5Gc.

SUBMITTER: Bergfeld AK

PROVIDER: S-EPMC3436522 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Metabolism of vertebrate amino sugars with N-glycolyl groups: elucidating the intracellular fate of the non-human sialic acid N-glycolylneuraminic acid.

Bergfeld Anne K AK Pearce Oliver M T OM Diaz Sandra L SL Pham Tho T Varki Ajit A

The Journal of biological chemistry 20120612 34

The two major mammalian sialic acids are N-acetylneuraminic acid and N-glycolylneuraminic acid (Neu5Gc). The only known biosynthetic pathway generating Neu5Gc is the conversion of CMP-N-acetylneuraminic acid into CMP-Neu5Gc, which is catalyzed by the CMP-Neu5Ac hydroxylase enzyme. Given the irreversible nature of this reaction, there must be pathways for elimination or degradation of Neu5Gc, which would allow animal cells to adjust Neu5Gc levels to their needs. Although humans are incapable of s ...[more]

PMID: 22692205

Similar Datasets

Project description:The outermost positions of mammalian cell-surface glycans are predominantly occupied by the sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). To date, hydroxylation of CMP-Neu5Ac resulting in the conversion into CMP-Neu5Gc is the only known enzymatic reaction in mammals to synthesize a monosaccharide carrying an N-glycolyl group. In our accompanying paper (Bergfeld, A. K., Pearce, O. M., Diaz, S. L., Pham, T., and Varki, A. (2012) J. Biol. Chem. 287, jbc.M112.363549), we report a metabolic pathway for degradation of Neu5Gc, demonstrating that N-acetylhexosamine pathways are tolerant toward the N-glycolyl substituent of Neu5Gc breakdown products. In this study, we show that exogenously added N-glycolylgalactosamine (GalNGc) serves as a precursor for Neu5Gc de novo biosynthesis, potentially involving seven distinct mammalian enzymes. Following the GalNAc salvage pathway, UDP-GalNGc is epimerized to UDP-GlcNGc, which might compete with the endogenous UDP-GlcNAc for the sialic acid biosynthetic pathway. Using UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase-deficient cells, we confirm that conversion of GalNGc into Neu5Gc depends on this key enzyme of sialic acid biosynthesis. Furthermore, we demonstrate by mass spectrometry that the metabolic intermediates UDP-GalNGc and UDP-GlcNGc serve as substrates for assembly of most major classes of cellular glycans. We show for the first time incorporation of GalNGc and GlcNGc into chondroitin/dermatan sulfates and heparan sulfates, respectively. As demonstrated by structural analysis, N-glycolylated hexosamines were found in cellular gangliosides and incorporated into Chinese hamster ovary cell O-glycans. Remarkably, GalNAc derivatives altered the overall O-glycosylation pattern as indicated by the occurrence of novel O-glycan structures. This study demonstrates that mammalian N-acetylhexosamine pathways and glycan assembly are surprisingly tolerant toward the N-glycolyl substituent.

Project description:The O-GlcNAc modification involves the attachment of single ?-O-linked N-acetylglucosamine residues to serine and threonine residues of nucleocytoplasmic proteins. Interestingly, previous biochemical and structural studies have shown that O-GlcNAcase (OGA), the enzyme that removes O-GlcNAc from proteins, has an active site pocket that tolerates various N-acyl groups in addition to the N-acetyl group of GlcNAc. The remarkable sequence and structural conservation of residues comprising this pocket suggest functional importance. We hypothesized this pocket enables processing of metabolic variants of O-GlcNAc that could be formed due to inaccuracy within the metabolic machinery of the hexosamine biosynthetic pathway. In the accompanying paper (Bergfeld, A. K., Pearce, O. M., Diaz, S. L., Pham, T., and Varki, A. (2012) J. Biol. Chem. 287, 28865-28881), N-glycolylglucosamine (GlcNGc) was shown to be a catabolite of NeuNGc. Here, we show that the hexosamine salvage pathway can convert GlcNGc to UDP-GlcNGc, which is then used to modify proteins with O-GlcNGc. The kinetics of incorporation and removal of O-GlcNGc in cells occur in a dynamic manner on a time frame similar to that of O-GlcNAc. Enzymatic activity of O-GlcNAcase (OGA) toward a GlcNGc glycoside reveals OGA can process glycolyl-containing substrates fairly efficiently. A bacterial homolog (BtGH84) of OGA, from a human gut symbiont, also processes O-GlcNGc substrates, and the structure of this enzyme bound to a GlcNGc-derived species reveals the molecular basis for tolerance and binding of GlcNGc. Together, these results demonstrate that analogs of GlcNAc, such as GlcNGc, are metabolically viable species and that the conserved active site pocket of OGA likely evolved to enable processing of mis-incorporated analogs of O-GlcNAc and thereby prevent their accumulation. Such plasticity in carbohydrate processing enzymes may be a general feature arising from inaccuracy in hexosamine metabolic pathways.

Project description:Spherical nucleic acid (SNA) nanoparticle conjugates are a class of bionanomaterials that are extremely potent in many biomedical applications. Their unique ability to enter multiple mammalian cell types as single-entity agents arises from their novel three-dimensional architecture, which consists of a dense shell of highly oriented oligonucleotides chemically attached typically to a gold nanoparticle core. This architecture allows SNAs to engage certain cell surface receptors to facilitate entry. Here, we report studies aimed at determining the intracellular fate of SNAs and the trafficking events that occur inside C166 mouse endothelial cells after cellular entry. We show that SNAs traffic through the endocytic pathway into late endosomes and reside there for up to 24 h after incubation. Disassembly of oligonucleotides from the nanoparticle core is observed 16 h after cellular entry, most likely due to degradation by enzymes such as DNase II localized in late endosomes. Our observations point to these events being likely independent of core composition and treatment conditions, and they do not seem to be particularly dependent upon oligonucleotide sequence. Significantly and surprisingly, the SNAs do not enter the lysosomes under the conditions studied. To independently track the fate of the particle core and the fluorophore-labeled oligonucleotides that comprise its shell, we synthesized a novel class of quantum dot SNAs to determine that as the SNA structures are broken down over the 24 h time course of the experiment, the oligonucleotide fragments are recycled out of the cell while the nanoparticle core is not. This mechanistic insight points to the importance of designing and synthesizing next-generation SNAs that can bypass the degradation bottleneck imposed by their residency in late endosomes, and it also suggests that such structures might be extremely useful for endosomal signaling pathways by engaging receptors that are localized within the endosome.

Dataset Information

Metabolism of vertebrate amino sugars with N-glycolyl groups: elucidating the intracellular fate of the non-human sialic acid N-glycolylneuraminic acid.

Publications

Metabolism of vertebrate amino sugars with N-glycolyl groups: elucidating the intracellular fate of the non-human sialic acid N-glycolylneuraminic acid.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets