To confirm whether the regulation of HATs and HDACsby veratric acid is associated with histone acetylation, wemeasured the overall level of acetylation of histones at theprotein level. The nuclear proteins were extracted from the cellstreated with veratric acid for 1 h prior to LPS stimulation for 1h. LPS stimulated the acetylation of histone H4; this acetylationwas downregulated by veratric acid in a dose-dependent manner. Bycontrast, no changes were observed in the acetylation levels ofhistone H3 following treatment with LPS and veratric acid (). As treatment with LY294002downregulated the acetylation of p300 and the phosphorylation ofATF-2, we hypothesized that LY294002 may attenuate the activity ofHAT p300 and ATF-2. To demonstrate our hypothesis, we compared theacetylation levels of histone H3 and H4 in the LY294002-treatedcells and those treated with veratric acid by western blotanalysis. LPS promoted the acetylation of histone H4, and thisacetylation was downregulated by LY294002, which coincided with theacetylation levels of histone H4 in the veratric acid-treated cells(). Hence, our resultsindicated that veratric acid suppressed the LPS-induced histone H3acetylation, and suggested that the suppression of the LPS-inducedhistone H4 acetylation by veratric acid may be accompanied by theregulation of the PI3K/Akt pathway.
Phosphorylation of LHCincreases (and dephosphorylation decreases) the proportion of excitationenergy transferred to photosystem I at the expense of photosystem II.
Regulation of thylakoid protein phosphorylation by …
Histone acetyltransferases (HATs) and histonedeacetylases (HDACs) are enzymes that mediate acetylation anddeacetylation at lysine residues of various proteins, includinghistones (). HATs are dividedinto 5 families: the GCN5-related -acetyltransferase (GNAT)family, represented by general control non-derepressible 5 (GCN5)and p300/CREB-binding protein (CBP)-associated factor (PCAF); thep300/CBP family, including p300 and CBP; the MYST family, includingTAT-interacting protein 60 (Tip60); general transcription factorHATs; and nuclear hormone-related HATs (). HDACs are classified into 4 classescontaining a total of 18 enzymes. There is sequence similaritybetween classical HDACs (class I, II and IV) whose activity isdependent on Zn. Class III includes the family ofsirtuins. In contrast to classical HDACs, the activity of class IIIsirtuins is dependent on NAD (). The acetylation of histones by HATsand the tight package of chromatin structure by HDACs are criticalto the control of gene expression. In resting cells, DNA is woundaround an octomer with 2 molecules each of the core histoneproteins, including H2A, H2B, H3 and H4. This chromatin structuresuppresses gene expression as the basal transcription complex isunable to bind to DNA. Conversely, once the cells are activated byexogenous stimulation, lysine residues of a long terminal of eachcore histone are acetylated by HATs, including CBP, p300 andCBP/p300 co-activators, reducing the electrical charge of corehistones. Thereby, the chromatin structure is transformed from theclosed form to the opened conformation, allowing the binding of RNApolymerase II and the initiation of transcription (). By contrast, removal of acetylgroup by HDAC repacks chromatin and causes gene silencing (). Thus, histone acetylation isclosely linked to the induction of pro-inflammatory geneexpression, and is considered a promising target for the treatmentof inflammatory diseases.
tmp94F2 | Phosphorylation | Cyanobacteria
Nitric oxide (NO) is one of the key elements in the complex signalling pathway leading to stomatal closure by inducing reversible protein phosphorylation and Carelease from intracellular stores. As photosynthesis in guard cells also contributes to stomatal function, the aim of this study was to explore the potential role of NO as a photosynthetic regulator. This work provides the first description of the reversible inhibition of the effect of NO on guard cell photosynthetic electron transport. Pulse amplitude modulation (PAM) chlorophyll fluorescence measurements on individual stomata of peeled abaxial epidermal strips indicated that exogenously applied 450nM NO rapidly increases the relative fluorescence yield, followed by a slow and constant decline. It was found that NO instantly decreases photochemical fluorescence quenching coefficients (qP and qL), the operating quantum efficiency of photosystem II (ΦPSII), and non-photochemical quenching (NPQ) to close to zero with different kinetics. NO caused a decrease in NPQ, which is followed by a slow and continuous rise. removal of NO from the medium surrounding the epidermal strips using a rapid liquid perfusion system showed that the effect of NO on qP and ΦPSII, and thus on the linear electron transport rate through PSII (ETR), is reversible, and the constant rise in NPQ disappears, resulting in a near steady-state value. reversible inhibition by NO of the ETR could be restored by bicarbonate, a compound known to compete with NO for one of the two coordination sites of the non-haem iron (II) in the QAFeQB complex.
Protein phosphorylation is a mechanism used by eukaryotes ..
In the crude extracts from light- and dark-adapted leaves in the presence of a physiological concentration of malate (20 mM), PEPC activity comparable to the photosynthetic rate was obtained only from the light-adapted leaves in the presence of metabolites indicating that both light-induced protein phosphorylation and metabolic activators were essential for PEPC activation during photosynthesis.