O-linked beta-N-acetylglucosamine: a new piece of the cardioprotection puzzle?

Protein-ligand interaction study of CpOGA in complex with GlcNAcstatin

The GlcNAcstatin is a potent inhibitor of O-glycoprotein 2-acetamino-2-deoxy-β-D-glucopyranosidase, which has been related with type II diabetes and neurodegenerative disorders. Herein, hybrid quantum mechanics/molecular mechanics, molecular dynamics simulations, and potential of mean force were employed to study the interactions established between GlcNAcstatin and a bacterial O-GlcNAcase enzyme from Clostridium perfringens. The results reveal that the imidazole nitrogen atom of GlcNAcstatin has shown a better interaction with the active site of Clostridium perfringens in its protonated form, which is compatible with a substrate-assisted reaction mechanism involving two conserved aspartate residues (297 and 298). Furthermore, the quantum mechanics/molecular mechanics-molecular dynamics simulations appointed a strong interaction between Asp401, Asp298, and Asp297 residues and the GlcNAcstatin inhibitor, which is in accordance with experimental data. Lastly, these results may contribute to understand the molecular mechanism of inhibition of Clostridium perfringens by GlcNAcstatin inhibitor and, consequently, this study might be useful to design new molecules with more interesting inhibitory activity.

Computational analysis of human OGA structure in complex with PUGNAc and NAG-thiazoline derivatives

The substitution of serine and threonine residues in nucleocytoplasmic proteins with 2-acetamido-2-deoxy-β-D-glucopyranose (O-GlcNAc) residues is an essential post-translational modification found in many multicellular eukaryotes. O-glycoprotein 2-acetamino-2-deoxy-β-D-glucopyranosidase (O-GlcNAcase) hydrolyzes O-GlcNAc residues from post-translationally modified serine/threonine residues of nucleocytoplasmic protein. O-GlcNAc has been implicated in several disease states such as cancer, Alzheimer's disease, and type II diabetes. For this paper, a model of the human O-GlcNAcase (hOGA) enzyme based on the X-ray structures of bacterial Clostridium perfringens (CpNagJ) and Bacteroides thetaiotaomicrometer (BtOGA) homologues has been generated through molecular homology modeling. In addition, molecular docking, molecular dynamics (MD) simulations, and Linear Interaction Energy (LIE) were employed to determine the bind for derivatives of two potent inhibitors: O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) and 1,2-dideoxy-2'-methyl-R-D-glucopyranoso-[2,1-d]-Δ2'-thiazoline (NAG-thiazoline), with hOGA. The results show that the binding free energy calculations using the Linear Interaction Energy (LIE) are correlated with inhibition constant values. Therefore, the model of the human O-GlcNAcase (hOGA) obtained here may be used as a target for rational design of new inhibitors.

Cardioprotective pathways during reperfusion: focus on redox signaling and other modalities of cell signaling

Post-ischemic reperfusion may result in reactive oxygen species (ROS) generation, reduced availability of nitric oxide (NO•), Ca(2+)overload, prolonged opening of mitochondrial permeability transition pore, and other processes contributing to cell death, myocardial infarction, stunning, and arrhythmias. With the discovery of the preconditioning and postconditioning phenomena, reperfusion injury has been appreciated as a reality from which protection is feasible, especially with postconditioning, which is under the control of physicians. Potentially cooperative protective signaling cascades are recruited by both pre- and postconditioning. In these pathways, phosphorylative/dephosphorylative processes are widely represented. However, cardioprotective modalities of signal transduction also include redox signaling by ROS, S-nitrosylation by NO• and derivative, S-sulfhydration by hydrogen sulfide, and O-linked glycosylation with beta-N-acetylglucosamine. All these modalities can interact and regulate an entire pathway, thus influencing each other. For instance, enzymes can be phosphorylated and/or nitrosylated in specific and/or different site(s) with consequent increase or decrease of their specific activity. The cardioprotective signaling pathways are thought to converge on mitochondria, and various mitochondrial proteins have been identified as targets of these post-transitional modifications in both pre- and postconditioning.

Dysregulation of the nutrient/stress sensor O-GlcNAcylation is involved in the etiology of cardiovascular disorders, type-2 diabetes and Alzheimer's disease

O-GlcNAcylation is widespread within the cytosolic and nuclear compartments of cells. This post-translational modification is likely an indicator of good health since its intracellular level correlates with the availability of extracellular glucose. Apart from its status as a nutrient sensor, O-GlcNAcylation may also act as a stress sensor since it exerts its fundamental effects in response to stress. Several studies report that the cell quickly responds to an insult by elevating O-GlcNAcylation levels and by unmasking a newly described Hsp70-GlcNAc binding property. From a more practical point of view, it has been shown that O-GlcNAcylation impairments contribute to the etiology of cardiovascular diseases, type-2 diabetes and Alzheimer's disease (AD), three illnesses common in occidental societies. Many studies have demonstrated that O-GlcNAcylation operates as a powerful cardioprotector and that by raising O-GlcNAcylation levels, the organism more successfully resists trauma-hemorrhage and ischemia/reperfusion injury. Recent data have also shown that insulin resistance and, more broadly, type-2 diabetes can be controlled by O-GlcNAcylation of the insulin pathway and O-GlcNAcylation of the gluconeogenesis transcription factors FoxO1 and CRCT2. Lastly, the finding that AD may correspond to a type-3 diabetes offers new perspectives into the knowledge of the neuropathology and into the search for new therapeutic avenues.