O-GlcNAc modification prevents peptide-dependent acceleration of α-synuclein aggregation

Sweet relief: the Parkinson's disease-associated protein α-synuclein is post-translationally modified by N-acetylglucosamine (O-GlcNAc), but the biochemical consequences are unknown. Here we show that an O-GlcNAc-modified peptide does not participate in α-synuclein aggregation, thus suggesting that O-GlcNAc might directly inhibit aggregation in cells. Source: Marotta, N.P. et al. Chembiochem 13(18), 2665-2670 (2012).

November 9th, 2012|Tags: , , |

Structural snapshots of the reaction coordinate for O-GlcNAc transferase

Visualization of the reaction coordinate undertaken by glycosyltransferases has remained elusive but is critical for understanding this important class of enzyme. Using substrates and substrate mimics, we describe structural snapshots of all species along the kinetic pathway for human O-linked β-N-acetylglucosamine transferase (O-GlcNAc transferase), an intracellular enzyme that catalyzes installation of a dynamic post-translational modification. [...]

October 28th, 2012|Tags: , |

O-linked β-N-acetylglucosaminidase inhibitor attenuates β-amyloid plaque and rescues memory impairment

Deposition of β-amyloid (Aβ) as senile plaques and disrupted glucose metabolism are two main characteristics of Alzheimer's disease (AD). It is unknown, however, how these two processes are related in AD. Here we examined the relationship between O-GlcNAcylation, which is a glucose level-dependent post-translational modification that adds O-linked β-N-acetylglucosamine (O-GlcNAc) to proteins, and Aβ production [...]

April 11th, 2012|Tags: , , , , |

Increasing O-GlcNAc slows neurodegeneration and stabilizes tau against aggregation

Oligomerization of tau is a key process contributing to the progressive death of neurons in Alzheimer’s disease. Tau is modified by O-linked N-acetylglucosamine (O-GlcNAc), and O-GlcNAc can influence tau phosphorylation in certain cases. We therefore speculated that increasing tau O-GlcNAc could be a strategy to hinder pathological tau-induced neurodegeneration. Here we found that treatment of [...]

February 26th, 2012|Tags: , , , , , |

Insights into O-linked N-acetylglucosamine ((0-9)O-GlcNAc) processing and dynamics through kinetic analysis of O-GlcNAc transferase and O-GlcNAcase activity on protein substrates

Cellular O-linked N-acetylglucosamine (O-GlcNAc) levels are modulated by two enzymes: uridine diphosphate-N-acetyl-D-glucosamine:polypeptidyltransferase (OGT) and O-GlcNAcase (OGA). To quantitatively address the activity of these enzymes on protein substrates, we generated five structurally diverse proteins in both unmodified and O-GlcNAc-modified states. We found a remarkably invariant upper limit for k(cat)/K(m) values for human OGA (hOGA)-catalyzed processing of [...]

February 6th, 2012|Tags: , , |

Hijacking a biosynthetic pathway yields a glycosyltransferase inhibitor within cells

Glycosyltransferases are ubiquitous enzymes that catalyze the assembly of glycoconjugates throughout all kingdoms of nature. A long-standing problem is the rational design of probes that can be used to manipulate glycosyltransferase activity in cells and tissues. Here we describe the rational design and synthesis of a nucleotide sugar analog (Ac-5SGlcNAc) that inhibits, with high potency [...]

January 23rd, 2011|Tags: , , , |

Elevation of Global O-GlcNAc in rodents using a selective O-GlcNAcase inhibitor does not cause insulin resistance or perturb glucohomeostasis

The O-GlcNAc modification is proposed to be a nutrient sensor with studies suggesting that global increases in O-GlcNAc levels cause insulin resistance and impaired glucohomeostasis. We address this hypothesis by using a potent and selective inhibitor of O-GlcNAcase, known as NButGT, in a series of in vivo studies. Treatment of rats and mice with NButGT, [...]

September 24th, 2010|Tags: , |

Inhibition of O-GlcNAcase using a potent and cell-permeable inhibitor does not induce insulin resistance in 3T3-L1 adipocytes

To probe increased O-GlcNAc levels as an independent mechanism governing insulin resistance in 3T3-L1 adipocytes, a new class of O-GlcNAcase (OGA) inhibitor was studied. 6-Acetamido-6-deoxy-castanospermine (6-Ac-Cas) is a potent inhibitor of OGA. The structure of 6-Ac-Cas bound in the active site of an OGA homolog reveals structural features contributing to its potency. Treatment of 3T3-L1 [...]

September 24th, 2010|Tags: , |

Mapping O-GlcNAc modification sites on tau and generation of a site-specific O-GlcNAc tau antibody

The microtubule-associated protein tau is known to be post-translationally modified by the addition of N-acetyl-D: -glucosamine monosaccharides to certain serine and threonine residues. These O-GlcNAc modification sites on tau have been challenging to identify due to the inherent complexity of tau from mammalian brains and the fact that the O-GlcNAc modification typically has substoichiometric occupancy. [...]

August 13th, 2010|Tags: , , , |

Visualizing the reaction coordinate of an O-GlcNAc hydrolase

N-Acetylglucosamine beta-O-linked to serine and threonine residues of nucleocytoplasmic proteins (O-GlcNAc) has been linked to neurodegeneration, cellular stress response, and transcriptional regulation. Removal of O-GlcNAc is catalyzed by O-GlcNAcase (OGA) using a substrate-assisted catalytic mechanism. Here we define the reaction coordinate using chemical approaches and directly observe both a Michaelis complex and the oxazoline intermediate. [...]

February 17th, 2010|Tags: , |