The activity of the DNA repair enzyme hOGG1 can be directly modulated by ubiquinol.

The DNA of human cells suffers about 1.000-100.000 oxidative lesions per day. One of the most common defects in this category is represented by 7,8-dihydro-8-oxoguanine. There are numerous exogenous effects on DNA that induce the intracellular generation of 7, 8-dihydro-8-oxoguanine. Therefore, a quantitatively sufficient repair of all occurring oxidative damaged guanine bases is often only partially feasible, especially in advanced age. Inadequate removal of these damages can subsequently lead to mutations and thus to serious diseases. All these aspects represent a dangerous situation for an organism. However, it is suspected that the amount of the 8-oxoguanine DNA glycosylase can be actively regulated on the level of gene expression by the redox-active properties of ubiquinol and thus its protein expression can be controlled. Using an real-time base excision repair assay including a melting curve analysis, the activity of the human 8-oxoguanine DNA glycosylase 1 was measured under the influence of ubiquinol. It was possible to observe a concentration-dependent increase in the activity of the 8-oxoguanine DNA glycosylase 1 under the influence of ubiquinol for the first time, both on purified and commercially acquired enzyme as well as on enzyme isolated from mitochondria of human fibroblasts. An increase in activity of this enzyme based on a change in cellular redox state caused by ubiquinol could not be confirmed. In addition, an increased gene expression of 8-oxoguanine-DNA glycosylase 1 under ubiquinol could not be observed. However, there was a change in bifunctionality in favor of an increased N-glycosylase activity and a direct interaction between ubiquinol and 8-oxoguanine DNA glycosylase 1. We suggest that ubiquinol contributes to the dissolution of a human 8-oxoguanine DNA glycosylase 1 end-product complex that forms after cutting into the sugar-phosphate backbone of the DNA with the resulting unsaturated 3'-phospho-α, ß-aldehyde end and thereby inhibits further enzymatic steps.

Activation of Adhesion G Protein-coupled Receptors: AGONIST SPECIFICITY OF STACHEL SEQUENCE-DERIVED PEPTIDES.

Members of the adhesion G protein-coupled receptor (aGPCR) family carry an agonistic sequence within their large ectodomains. Peptides derived from this region, called the Stachel sequence, can activate the respective receptor. As the conserved core region of the Stachel sequence is highly similar between aGPCRs, the agonist specificity of Stachel sequence-derived peptides was tested between family members using cell culture-based second messenger assays. Stachel peptides derived from aGPCRs of subfamily VI (GPR110/ADGRF1, GPR116/ADGRF5) and subfamily VIII (GPR64/ADGRG2, GPR126/ADGRG6) are able to activate more than one member of the respective subfamily supporting their evolutionary relationship and defining them as pharmacological receptor subtypes. Extended functional analyses of the Stachel sequences and derived peptides revealed agonist promiscuity, not only within, but also between aGPCR subfamilies. For example, the Stachel-derived peptide of GPR110 (subfamily VI) can activate GPR64 and GPR126 (both subfamily VIII). Our results indicate that key residues in the Stachel sequence are very similar between aGPCRs allowing for agonist promiscuity of several Stachel-derived peptides. Therefore, aGPCRs appear to be pharmacologically more closely related than previously thought. Our findings have direct implications for many aGPCR studies, as potential functional overlap has to be considered for in vitro and in vivo studies. However, it also offers the possibility of a broader use of more potent peptides when the original Stachel sequence is less effective.

A tethered agonist within the ectodomain activates the adhesion G protein-coupled receptors GPR126 and GPR133.

Adhesion G protein-coupled receptors (aGPCRs) comprise the second largest yet least studied class of the GPCR superfamily. aGPCRs are involved in many developmental processes and immune and synaptic functions, but the mode of their signal transduction is unclear. Here, we show that a short peptide sequence (termed the Stachel sequence) within the ectodomain of two aGPCRs (GPR126 and GPR133) functions as a tethered agonist. Upon structural changes within the receptor ectodomain, this intramolecular agonist is exposed to the seven-transmembrane helix domain, which triggers G protein activation. Our studies show high specificity of a given Stachel sequence for its receptor. Finally, the function of Gpr126 is abrogated in zebrafish with a mutated Stachel sequence, and signaling is restored in hypomorphic gpr126 zebrafish mutants upon exogenous Stachel peptide application. These findings illuminate a mode of aGPCR activation and may prompt the development of specific ligands for this currently untargeted GPCR family.