Metabolism of Vertebrate Amino Sugars with N-Glycolyl Groups

Bergfeld, Anne K.; Pearce, Oliver M.T.; Díaz, Sandra; Pham, Tho D.; Varki, Ajit

doi:10.1074/jbc.m112.363549

Cited by 70 publications

(38 citation statements)

References 83 publications

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“…The half‐life in normal liver, where glycans are primarily protein bound, is ≈33 h; however, the half‐life in brain, where glycans are primarily lipid bound, varies greatly between 4 and 45 days . Pulsing with Neu5Gc in a human B‐cell lymphoma cell line yielded a similar half‐life (≈4 days) to what has been observed in brain tissue …”

Section: Biochemical Consequences Of Cmah Loss In Humanssupporting

confidence: 60%

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N‐Glycolylneuraminic Acid

Okerblom

Varki

2017

ChemBioChem

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About 2–3 million years ago, Alu‐mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti‐Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host–pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human‐like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper‐reactive immune system, a human‐like tendency for delayed wound healing, late‐onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human‐adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human‐specific processes and pathologies involving sialic acid biology that have yet to be explored.

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Section: Biochemical Consequences Of Cmah Loss In Humanssupporting

confidence: 60%

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N‐Glycolylneuraminic Acid

Okerblom

Varki

2017

ChemBioChem

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“…Importantly, tachyzoites incorporate Ac 4 GlcNAz and Ac 4 GlcNAlk in a concentration and time dependent manner (Figures 1B–C, S1–6). Previous studies have demonstrated that the N -acyl chain of GlcNAc and related analoggs can be cleaved in cells and subsequently used for protein acetylation [47, 48]. To investigate whether the N -acyl units of Ac 4 GlcNAz or Ac 4 GlcNAlk were removed and appended to Toxoplasma proteins, we synthesized N -azido and N -alkynyl acetyl units and examined their incorporation (Figure 1D, S7).…”

Section: Resultsmentioning

confidence: 99%

Extracellular Toxoplasma gondii tachyzoites metabolize and incorporate unnatural sugars into cellular proteins

Nazarova

Ochoa

Morrissette

et al. 2016

Microbes and Infection

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Toxoplasma gondii is an obligate intracellular parasite that infects all nucleated cell types in diverse warm-blooded organisms. Many of the surface antigens and effector molecules secreted by the parasite during invasion and intracellular growth are modified by glycans. Glycosylated proteins in the nucleus and cytoplasm have also been reported. Despite their prevalence, the complete inventory and biological significance of glycosylated proteins in Toxoplasma remains unknown. In this study, we aimed to globally profile parasite glycoproteins using a bioorthogonal chemical reporter strategy. This strategy involves the metabolic incorporation of unnatural functional groups (i.e., “chemical reporters”) into Toxoplasma glycans, followed by covalent labeling with visual probes or affinity tags. The two-step approach enables the visualization and identification of newly biosynthesized glycoconjugates in the parasite. Using a buffer that mimics intracellular conditions, extracellular Toxoplasma tachyzoites were found to metabolize and incorporate unnatural sugars (equipped with bioorthogonal functional groups) into diverse proteins. Covalent chemistries were used to visualize and retrieve these labeled structures. Subsequent mass spectrometry analysis revealed 89 unique proteins. This survey identified novel proteins as well as previously characterized proteins from lectin affinity analyses.

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“…Once there, free Neu5Ac or Neu5Gc must be transported to the nucleus to be CMP-activated (55) and then to the Golgi lumen to be conjugated onto glycoproteins or glycolipids. The half-life of free sialic acids fed to cells is ~4 days (56), so most of it should be utilized in this way after feeding. However, sialic acid degradation to their acetate (from Neu5Ac) and glycolate (from Neu5Gc) metabolites does occur during the constant recycling of endogenous Neu5Ac or Neu5Gc sialic acids during maintenance of steady state (56–59).…”

Section: Resultsmentioning

confidence: 99%

“…The half-life of free sialic acids fed to cells is ~4 days (56), so most of it should be utilized in this way after feeding. However, sialic acid degradation to their acetate (from Neu5Ac) and glycolate (from Neu5Gc) metabolites does occur during the constant recycling of endogenous Neu5Ac or Neu5Gc sialic acids during maintenance of steady state (56–59). Similar to results observed between WT and Cmah −/− mice, the feeding of Neu5Gc to peritoneal macrophages isolated from Cmah −/− mice indeed increased their Neu5Gc content (Supp.…”

Section: Resultsmentioning

confidence: 99%

“…Given the global impact of eliminating tens of millions of N-glycolyl groups from cells via CMAH loss, there are multiple possible (and mutually non-exclusive) mechanisms contributing to our findings. For example, cytosolic degradation of excess Neu5Gc can result in generation of glycolate (instead of acetate generated from Neu5Ac breakdown) (56), with the possibility of a systematic alteration in cell metabolism. Previously published microarray data in WT and Cmah−/− mouse muscle implicated CREB1, C/EBPα, and C/EBPβ as candidate transcription factors affected by Cmah loss (14).…”

Section: Discussionmentioning

confidence: 99%

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Loss of CMAH during Human Evolution Primed the Monocyte–Macrophage Lineage toward a More Inflammatory and Phagocytic State

Okerblom

Schwarz

Olson

et al. 2017

The Journal of Immunology

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Humans and chimpanzees are more sensitive to endotoxin than mice or monkeys, but any underlying differences in inflammatory physiology have not been fully described or understood. We studied innate immune responses in Cmah−/− mice, emulating human loss of the gene encoding production of Neu5Gc, a major cell surface sialic acid. CMAH loss occurred ~2-3 million years ago, after the common ancestor of humans and chimpanzees, perhaps contributing to speciation of the genus Homo. Cmah−/− mice manifested a decreased survival in endotoxemia following bacterial lipopolysaccharide (LPS) injection. Macrophages from Cmah−/− mice secreted more inflammatory cytokines with LPS-stimulation and showed more phagocytic activity. Macrophages and whole blood from Cmah−/− mice also killed bacteria more effectively. Metabolic re-introduction of Neu5Gc into Cmah−/− macrophages suppressed these differences. Cmah−/− mice also showed enhanced bacterial clearance during sub-lethal lung infection. Although monocytes and monocyte-derived macrophages from humans and chimpanzees exhibited marginal differences in LPS responses, human monocyte-derived macrophages killed E. coli and ingested E. coli bioparticles better. Metabolic re-introduction of Neu5Gc into human macrophages suppressed these differences. While multiple mechanisms are likely involved, one cause is altered expression of C/EBPβ, a transcription factor affecting macrophage function. Loss of Neu5Gc in Homo likely had complex effects on immunity, providing greater capabilities to clear sub-lethal bacterial challenges, possibly at the cost of endotoxic shock risk. This trade-off may have provided a selective advantage when Homo transitioned to butchery using stone tools. The findings may also explain why the Cmah−/− state alters severity in mouse models of human disease.

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Metabolism of Vertebrate Amino Sugars with N-Glycolyl Groups

Cited by 70 publications

References 83 publications

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N‐Glycolylneuraminic Acid

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N‐Glycolylneuraminic Acid

Extracellular Toxoplasma gondii tachyzoites metabolize and incorporate unnatural sugars into cellular proteins

Loss of CMAH during Human Evolution Primed the Monocyte–Macrophage Lineage toward a More Inflammatory and Phagocytic State

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