26 research outputs found
Nuclear Magnetic Resonance
Contains research objectives and reports on five research projects
Extreme Features of the Galdieria sulphuraria Organellar Genomes: A Consequence of Polyextremophily?
Nuclear genome sequencing from extremophilic eukaryotes has revealed clues about the mechanisms of adaptation to extreme
environments, but the functional consequences of extremophily on organellar genomes are unknown. To address this issue, we
assembled the mitochondrial and plastid genomes from a polyextremophilic red alga, Galdieria sulphuraria strain 074 W, and performed
a comparative genomic analysis with other red algae and more broadly across eukaryotes. The mitogenome is highlyreduced
in size and genetic content and exhibits the highest guanineâcytosine skew of any known genome and the fastest substitution rate
among all red algae. The plastid genome contains a large number of intergenic stem-loop structures but is otherwise rather typical in
size, structure, and content in comparison with other red algae. We suggest that these unique genomic modifications result not only
from the harsh conditions in which Galdieria lives but also from its unusual capability to grow heterotrophically, endolithically, and
in the dark. These conditions place additional mutational pressures on the mitogenome due to the increased reliance on the mitochondrion
for energy production, whereas the decreased reliance on photosynthesis and the presence of numerous stem-loop
structures may shield the plastome from similar genomic stress
5âHT<sub>4</sub> Receptors Constitutively Promote the Non-Amyloidogenic Pathway of APP Cleavage and Interact with ADAM10
In addition to the amyloidogenic pathway, amyloid precursor
protein
(APP) can be cleaved by α-secretases, producing soluble and
neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway)
and thus preventing the generation of pathogenic amyloid-ÎČ.
However, the mechanisms regulating APP cleavage by α-secretases
remain poorly understood. Here, we showed that expression of serotonin
type 4 receptors (5-HT<sub>4</sub>Rs) constitutively (without agonist
stimulation) induced APP cleavage by the α-secretase ADAM10
and the release of neuroprotective sAPPα in HEK-293 cells and
cortical neurons. This effect was independent of cAMP production.
Interestingly, we demonstrated that 5-HT<sub>4</sub> receptors physically
interacted with the mature form of ADAM10. Stimulation of 5-HT<sub>4</sub> receptors by an agonist further increased sAPPα secretion,
and this effect was mediated by cAMP/Epac signaling. These findings
describe a new mechanism whereby a GPCR constitutively stimulates
the cleavage of APP by α-secretase and promotes the nonamyloidogenic
pathway of APP processing
Closure of the Venus flytrap module of mGlu8 receptor and the activation process: Insights from mutations converting antagonists into agonists
Ca(2+), pheromones, sweet taste compounds, and the main neurotransmitters glutamate and Îł-aminobutyric acid activate G protein-coupled receptors (GPCRs) that constitute the GPCR family 3. These receptors are dimers, and each subunit has a large extracellular domain called a Venus flytrap module (VFTM), where agonists bind. This module is connected to a heptahelical domain that activates G proteins. Recently, the structure of the dimer of mGlu1 VFTMs revealed two important conformational changes resulting from glutamate binding. First, agonists can stabilize a closed state of at least one VFTM in the dimer. Second, the relative orientation of the two VFTMs in the dimer is different in the presence of glutamate, such that their C-terminal ends (which are connected to the G protein-activating heptahelical domain) become closer by more than 20 â«. This latter change in orientation has been proposed to play a key role in receptor activation. To elucidate the respective role of VFTM closure and the change in orientation of the VFTMs in family 3 GPCR activation, we analyzed the mechanism of action of the mGlu8 receptor antagonists ACPT-II and MAP4. Molecular modeling studies suggest that these two compounds prevent the closure of the mGlu8 VFTM because of ionic and steric hindrance, respectively. We show here that the replacement of the residues responsible for these hindrances (Asp-309 and Tyr-227, respectively) by Ala allows ACPT-II or MAP4 to fully activate the receptors. These data are consistent with the requirement of the VFTM closure for family 3 GPCR activation