Elevation of global O-GlcNAc levels in 3T3-L1 adipocytes by selective inhibition of O-GlcNAcase does not induce insulin resistance

The O-GlcNAc post-translational modification is considered to act as a sensor of nutrient flux through the hexosamine biosynthetic pathway. A cornerstone of this hypothesis is that global elevation of protein O-GlcNAc levels, typically induced with the non-selective O-GlcNAcase inhibitor PUGNAc (O-(2-acetamido-2-deoxy-D-glycopyranosylidene) amino-N-phenylcarbamate), causes insulin resistance in adipocytes. Here we address the potential link between elevated [...]

October 8th, 2008|Tags: , |

A potent mechanism-inspired O-GlcNAcase inhibitor that blocks phosphorylation of tau in vivo

Pathological hyperphosphorylation of the microtubule-associated protein tau is characteristic of Alzheimer’s disease (AD) and the associated tauopathies. The reciprocal relationship between phosphorylation and O-GlcNAc modification of tau and reductions in O-GlcNAc levels on tau in AD brain offers motivation for the generation of potent and selective inhibitors that can effectively enhance O-GlcNAc in vertebrate brain. [...]

June 29th, 2008|Tags: , , , , |

Structure of an O-GlcNAc transferase homolog provides insight into intracellular glycosylation

N-Acetylglucosamine (O-GlcNAc) modification of proteins provides a mechanism for the control of diverse cellular processes through a dynamic interplay with phosphorylation. UDP-GlcNAc:polypeptidyl transferase (OGT) catalyzes O-GlcNAc addition. The structure of an intact OGT homolog and kinetic analysis of human OGT variants reveal a contiguous superhelical groove that directs substrates to the active site. Source: Martinez-Fleites, [...]

June 8th, 2008|Tags: , |

Analysis of PUGNAc and NAG-thiazoline as transition state analogues for human O-GlcNAcase: mechanistic and structural insights into inhibitor selectivity and transition state poise

O-GlcNAcase catalyzes the cleavage of beta-O-linked 2-acetamido-2-deoxy-beta-d-glucopyranoside (O-GlcNAc) from serine and threonine residues of post-translationally modified proteins. Two potent inhibitors of this enzyme are O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) and 1,2-dideoxy-2′-methyl-alpha-d-glucopyranoso[2,1-d]-Delta2′-thiazoline (NAG-thiazoline). Derivatives of these inhibitors differ in their selectivity for human O-GlcNAcase over the functionally related human lysosomal beta-hexosamindases, with PUGNAc derivatives showing modest selectivities and NAG-thiazoline [...]

January 24th, 2007|Tags: , |

Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity

O-GlcNAc is an abundant post-translational modification of serine and threonine residues of nucleocytoplasmic proteins. This modification, found only within higher eukaryotes, is a dynamic modification that is often reciprocal to phosphorylation. In a manner analogous to phosphatases, a glycoside hydrolase termed O-GlcNAcase cleaves O-GlcNAc from modified proteins. Enzymes with high sequence similarity to human O-GlcNAcase [...]

March 26th, 2006|Tags: , |

Identification of Asp174 and Asp175 as the key catalytic residues of human O-GlcNAcase by functional analysis of site-directed mutants

O-GlcNAcase is a family 84 beta-N-acetylglucosaminidase catalyzing the hydrolytic cleavage of beta-O-linked 2-acetamido-2-deoxy-d-glycopyranose (O-GlcNAc) from serine and threonine residues of posttranslationally modified proteins. O-GlcNAcases use a double-displacement mechanism involving formation and breakdown of a transient bicyclic oxazoline intermediate. The key catalytic residues of any family 84 enzyme facilitating this reaction, however, are unknown. Two mutants [...]

March 21st, 2006|Tags: , |

O-GlcNAcase uses substrate-assisted catalysis: kinetic analysis and development of highly selective mechanism-inspired inhibitors

The post-translational modification of serine and threonine residues of nucleocytoplasmic proteins with 2-acetamido-2-deoxy-d-glucopyranose (GlcNAc) is a reversible process implicated in multiple cellular processes. The enzyme O-GlcNAcase catalyzes the cleavage of beta-O-linked GlcNAc (O-GlcNAc) from modified proteins and is a member of the family 84 glycoside hydrolases. The family 20 beta-hexosaminidases bear no apparent sequence similarity [...]

March 28th, 2005|Tags: , |